<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
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      background: #ffffff;
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      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      user-select: none;
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    .diagram-grid {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      width: 100%;
      max-width: 580px;
      margin-top: 4px;
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    .panel {
      flex: 1;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 8px 6px;
      text-align: center;
      display: flex;
      flex-direction: column;
      align-items: center;
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    .panel-title {
      font-size: 13px;
      font-weight: 700;
      color: #475569;
      margin-bottom: 6px;
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    .arrow-container {
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      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 2px;
      color: #b45309;
      font-weight: 700;
      font-size: 11px;
      min-width: 44px;
      text-align: center;
    }

    .arrow-icon {
      font-size: 20px;
      line-height: 1;
    }

    svg {
      width: 100%;
      max-width: 150px;
      height: 110px;
    }

    /* Nail Visual */
    .nail-container {
      width: 100%;
      max-width: 580px;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 12px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 8px 14px;
    }

    .nail-svg {
      width: 130px;
      height: 28px;
    }

    .status-text {
      font-size: 13px;
      font-weight: 700;
      color: #1e2945;
      min-width: 120px;
    }

    /* Slider */
    .controls {
      width: 100%;
      max-width: 580px;
      display: flex;
      flex-direction: column;
      gap: 4px;
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    .slider-labels {
      display: flex;
      justify-content: space-between;
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
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    input[type="range"] {
      width: 100%;
      height: 8px;
      border-radius: 4px;
      outline: none;
      -webkit-appearance: none;
      background: #e2e8f0;
      cursor: pointer;
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    input[type="range"]::-webkit-slider-thumb {
      -webkit-appearance: none;
      width: 22px;
      height: 22px;
      border-radius: 50%;
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      cursor: pointer;
    }

    .footer-badge {
      font-size: 12px;
      font-weight: 700;
      color: #9a3412;
      background: #ffedd5;
      border: 1px solid #fed7aa;
      padding: 5px 12px;
      border-radius: 20px;
      text-align: center;
    }
  </style>
</head>
<body>

  
  <div class="diagram-grid">
    
    <div class="panel">
      <div class="panel-title">Fe + O₂ (Reactants)</div>
      <svg viewBox="0 0 130 95">
        
        <g fill="#64748b" stroke="#334155" stroke-width="1.5">
          <circle cx="25" cy="30" r="11" />
          <circle cx="50" cy="30" r="11" />
          <circle cx="25" cy="55" r="11" />
          <circle cx="50" cy="55" r="11" />
          <text x="25" y="34" font-size="10" fill="#fff" font-weight="bold" text-anchor="middle" stroke="none">Fe</text>
          <text x="50" y="34" font-size="10" fill="#fff" font-weight="bold" text-anchor="middle" stroke="none">Fe</text>
          <text x="25" y="59" font-size="10" fill="#fff" font-weight="bold" text-anchor="middle" stroke="none">Fe</text>
          <text x="50" y="59" font-size="10" fill="#fff" font-weight="bold" text-anchor="middle" stroke="none">Fe</text>
        </g>
        
        <g fill="#ef4444" stroke="#991b1b" stroke-width="1.2">
          
          <line x1="88" y1="28" x2="104" y2="28" stroke="#991b1b" stroke-width="3" />
          <circle cx="88" cy="28" r="8" />
          <circle cx="104" cy="28" r="8" />
          <text x="88" y="31" font-size="8" fill="#fff" font-weight="bold" text-anchor="middle" stroke="none">O</text>
          <text x="104" y="31" font-size="8" fill="#fff" font-weight="bold" text-anchor="middle" stroke="none">O</text>

          
          <line x1="88" y1="58" x2="104" y2="58" stroke="#991b1b" stroke-width="3" />
          <circle cx="88" cy="58" r="8" />
          <circle cx="104" cy="58" r="8" />
          <text x="88" y="61" font-size="8" fill="#fff" font-weight="bold" text-anchor="middle" stroke="none">O</text>
          <text x="104" y="61" font-size="8" fill="#fff" font-weight="bold" text-anchor="middle" stroke="none">O</text>
        </g>
      </svg>
    </div>

    
    <div class="arrow-container">
      <div>Reaction</div>
      <div class="arrow-icon">→</div>
    </div>

    
    <div class="panel">
      <div class="panel-title">Fe₂O₃ Rust (Product)</div>
      <svg viewBox="0 0 130 95">
        
        <g stroke="#b45309" stroke-width="2.5">
          <line x1="28" y1="32" x2="52" y2="24" />
          <line x1="52" y1="24" x2="78" y2="32" />
          <line x1="78" y1="32" x2="102" y2="24" />
          
          <line x1="28" y1="32" x2="40" y2="60" />
          <line x1="52" y1="24" x2="65" y2="52" />
          <line x1="78" y1="32" x2="90" y2="60" />

          <line x1="40" y1="60" x2="65" y2="52" />
          <line x1="65" y1="52" x2="90" y2="60" />
        </g>
        
        <circle cx="28" cy="32" r="10" fill="#9a3412" stroke="#431407" stroke-width="1.2" />
        <text x="28" y="36" font-size="9" fill="#fff" font-weight="bold" text-anchor="middle">Fe</text>

        <circle cx="52" cy="24" r="7.5" fill="#ef4444" stroke="#991b1b" stroke-width="1" />
        <text x="52" y="27" font-size="7.5" fill="#fff" font-weight="bold" text-anchor="middle">O</text>

        <circle cx="78" cy="32" r="10" fill="#9a3412" stroke="#431407" stroke-width="1.2" />
        <text x="78" y="36" font-size="9" fill="#fff" font-weight="bold" text-anchor="middle">Fe</text>

        <circle cx="102" cy="24" r="7.5" fill="#ef4444" stroke="#991b1b" stroke-width="1" />
        <text x="102" y="27" font-size="7.5" fill="#fff" font-weight="bold" text-anchor="middle">O</text>

        <circle cx="40" cy="60" r="7.5" fill="#ef4444" stroke="#991b1b" stroke-width="1" />
        <text x="40" y="63" font-size="7.5" fill="#fff" font-weight="bold" text-anchor="middle">O</text>

        <circle cx="65" cy="52" r="10" fill="#9a3412" stroke="#431407" stroke-width="1.2" />
        <text x="65" y="56" font-size="9" fill="#fff" font-weight="bold" text-anchor="middle">Fe</text>

        <circle cx="90" cy="60" r="7.5" fill="#ef4444" stroke="#991b1b" stroke-width="1" />
        <text x="90" y="63" font-size="7.5" fill="#fff" font-weight="bold" text-anchor="middle">O</text>
      </svg>
    </div>
  </div>

  
  <div class="nail-container">
    <svg class="nail-svg" viewBox="0 0 160 30">
      <defs>
        
        <linearGradient id="cleanMetal" x1="0%" y1="0%" x2="0%" y2="100%">
          <stop offset="0%" stop-color="#cbd5e1" />
          <stop offset="50%" stop-color="#94a3b8" />
          <stop offset="100%" stop-color="#475569" />
        </linearGradient>
        
        <linearGradient id="rustMetal" x1="0%" y1="0%" x2="0%" y2="100%">
          <stop offset="0%" stop-color="#ea580c" />
          <stop offset="50%" stop-color="#c2410c" />
          <stop offset="100%" stop-color="#7c2d12" />
        </linearGradient>
      </defs>
      
      
      <g>
        <rect x="6" y="8" width="6" height="14" rx="1" fill="url(#cleanMetal)" />
        <polygon points="12,12 145,12 155,15 145,18 12,18" fill="url(#cleanMetal)" />
      </g>

      
      <g id="rustLayer" opacity="0">
        <rect x="6" y="8" width="6" height="14" rx="1" fill="url(#rustMetal)" />
        <polygon points="12,12 145,12 155,15 145,18 12,18" fill="url(#rustMetal)" />
        
        <circle cx="30" cy="14" r="1.5" fill="#431407" />
        <circle cx="65" cy="16" r="1.8" fill="#7c2d12" />
        <circle cx="95" cy="13" r="1.5" fill="#431407" />
        <circle cx="120" cy="15" r="1.7" fill="#7c2d12" />
        <circle cx="140" cy="14" r="1.3" fill="#431407" />
      </g>
    </svg>
    <div id="statusText" class="status-text">Day 1: Clean Iron</div>
  </div>

  
  <div class="controls">
    <div class="slider-labels">
      <span>Day 1 (Clean)</span>
      <span>Day 30 (Rusted)</span>
    </div>
    <input type="range" id="timeSlider" min="1" max="30" value="1" />
  </div>

  
  <div class="footer-badge">
    ✦ New Substance Formed • Irreversible Chemical Bond
  </div>

  <script>
    const slider = document.getElementById('timeSlider');
    const rustLayer = document.getElementById('rustLayer');
    const statusText = document.getElementById('statusText');

    slider.addEventListener('input', (e) => {
      const day = parseInt(e.target.value, 10);
      const progress = (day - 1) / 29;
      
      rustLayer.setAttribute('opacity', progress);

      if (day === 1) {
        statusText.textContent = 'Day 1: Clean Iron';
      } else if (day === 30) {
        statusText.textContent = 'Day 30: Fully Rusted';
      } else {
        statusText.textContent = `Day ${day}: Rusting...`;
      }
    });
  </script>
</body>
</html>

Physical Changes vs. Chemical Changes

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="1:1">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8fafc;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .header-bar {
      width: 100%;
      max-width: 480px;
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 10px;
      padding: 0 4px;
    }
    .title {
      font-size: 14px;
      font-weight: 700;
      color: #0f172a;
      letter-spacing: -0.01em;
    }
    .hint {
      font-size: 12px;
      font-weight: 500;
      color: #64748b;
      display: flex;
      align-items: center;
      gap: 4px;
    }

    .board {
      display: grid;
      grid-template-columns: repeat(2, 1fr);
      gap: 10px;
      width: 100%;
      max-width: 480px;
      aspect-ratio: 1 / 1;
    }

    .card-wrap {
      perspective: 900px;
      cursor: pointer;
      -webkit-tap-highlight-color: transparent;
    }

    .card-inner {
      position: relative;
      width: 100%;
      height: 100%;
      transform-style: preserve-3d;
      transition: transform 0.45s cubic-bezier(0.4, 0, 0.2, 1);
    }

    .card-wrap.flipped .card-inner {
      transform: rotateY(180deg);
    }

    .face {
      position: absolute;
      inset: 0;
      backface-visibility: hidden;
      -webkit-backface-visibility: hidden;
      border-radius: 12px;
      background: #ffffff;
      border: 1.5px solid #e2e8f0;
      display: flex;
      flex-direction: column;
      justify-content: space-between;
      align-items: center;
      padding: 12px 10px;
      text-align: center;
      user-select: none;
      box-shadow: 0 1px 3px rgba(0,0,0,0.04);
      transition: border-color 0.2s, box-shadow 0.2s;
    }

    .card-wrap:hover .face {
      border-color: #cbd5e1;
      box-shadow: 0 4px 8px rgba(0,0,0,0.06);
    }

    .face-back {
      transform: rotateY(180deg);
      background: #ffffff;
      justify-content: center;
      padding: 16px 12px;
      gap: 8px;
    }

    .graphic-box {
      flex: 1;
      width: 100%;
      display: flex;
      align-items: center;
      justify-content: center;
      position: relative;
      overflow: hidden;
    }

    svg {
      width: 100%;
      height: 100%;
      max-height: 90px;
      overflow: visible;
    }

    .card-label {
      font-size: 13px;
      font-weight: 700;
      color: #1e293b;
      margin-top: 4px;
      display: flex;
      align-items: center;
      gap: 4px;
    }

    .card-num {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      width: 18px;
      height: 18px;
      border-radius: 50%;
      font-size: 10px;
      font-weight: 800;
      color: #fff;
    }

    .badge-gas { background: #0284c7; }
    .badge-color { background: #7c3aed; }
    .badge-energy { background: #ea580c; }
    .badge-precip { background: #0d9488; }

    .back-title {
      font-size: 12px;
      font-weight: 800;
      text-transform: uppercase;
      letter-spacing: 0.05em;
    }

    .back-text {
      font-size: 12.5px;
      line-height: 1.4;
      color: #334155;
      font-weight: 500;
    }

    .back-tap-hint {
      font-size: 10px;
      color: #94a3b8;
      font-weight: 600;
      margin-top: 4px;
    }

    /* Animations */
    @keyframes bubbleRise {
      0% { transform: translateY(0) scale(0.8); opacity: 0; }
      30% { opacity: 0.9; }
      80% { opacity: 0.9; }
      100% { transform: translateY(-38px) scale(1.1); opacity: 0; }
    }

    .bubble-1 { animation: bubbleRise 2.2s infinite ease-in; }
    .bubble-2 { animation: bubbleRise 1.8s infinite 0.6s ease-in; }
    .bubble-3 { animation: bubbleRise 2.5s infinite 1.2s ease-in; }
    .bubble-4 { animation: bubbleRise 2.0s infinite 0.3s ease-in; }

    @keyframes flamePulse {
      0%, 100% { transform: scale(1); opacity: 0.95; }
      50% { transform: scale(1.06) translateY(-1px); opacity: 1; }
    }
    .flame-core { transform-origin: center bottom; animation: flamePulse 1.6s infinite ease-in-out; }

    @keyframes settleDown {
      0% { transform: translateY(-8px); opacity: 0.2; }
      50% { opacity: 0.8; }
      100% { transform: translateY(12px); opacity: 0; }
    }
    .precip-p1 { animation: settleDown 2.4s infinite ease-in; }
    .precip-p2 { animation: settleDown 2.8s infinite 0.8s ease-in; }
    .precip-p3 { animation: settleDown 2.2s infinite 1.4s ease-in; }

    @keyframes pulseGlow {
      0%, 100% { opacity: 0.3; }
      50% { opacity: 0.7; }
    }
    .glow-ring { animation: pulseGlow 2.5s infinite ease-in-out; }
  </style>
</head>
<body>

  <div class="header-bar">
    <div class="title">4 Clues of Chemical Change</div>
    <div class="hint">Tap card to flip ↺</div>
  </div>

  <div class="board">

    
    <div class="card-wrap" tabindex="0" role="button" aria-label="Gas Production evidence card">
      <div class="card-inner">
        <div class="face">
          <div class="graphic-box">
            <svg viewBox="0 0 100 90">
              
              <text x="50" y="16" font-size="10" font-weight="800" fill="#0284c7" text-anchor="middle" letter-spacing="0.5">CO₂ ↑</text>
              
              <path d="M 32 26 L 32 30 L 37 36 L 37 76 A 4 4 0 0 0 41 80 L 59 80 A 4 4 0 0 0 63 76 L 63 36 L 68 30 L 68 26 Z" fill="#e0f2fe" stroke="#0284c7" stroke-width="2" stroke-linejoin="round" />
              
              <path d="M 38 52 Q 50 50 62 52 L 62 76 A 3 3 0 0 1 59 79 L 41 79 A 3 3 0 0 1 38 76 Z" fill="#38bdf8" />
              
              <ellipse cx="50" cy="76" rx="9" ry="3" fill="#ffffff" opacity="0.9" />
              
              <circle class="bubble-1" cx="46" cy="54" r="2.5" fill="#ffffff" />
              <circle class="bubble-2" cx="54" cy="58" r="2" fill="#ffffff" />
              <circle class="bubble-3" cx="49" cy="62" r="3" fill="#ffffff" />
              <circle class="bubble-4" cx="43" cy="66" r="1.8" fill="#ffffff" />
              <circle class="bubble-2" cx="56" cy="46" r="2.2" fill="#bae6fd" />
              <circle class="bubble-1" cx="47" cy="38" r="2.8" fill="#bae6fd" />
            </svg>
          </div>
          <div class="card-label">
            <span class="card-num badge-gas">1</span>
            <span>Gas Bubbles</span>
          </div>
        </div>
        <div class="face face-back" style="border-top: 4px solid #0284c7;">
          <div class="back-title" style="color: #0284c7;">Gas Production</div>
          <div class="back-text">Baking soda and vinegar react chemically to produce carbon dioxide gas bubbles.</div>
          <div class="back-tap-hint">tap to flip back</div>
        </div>
      </div>
    </div>

    
    <div class="card-wrap" tabindex="0" role="button" aria-label="Color Change evidence card">
      <div class="card-inner">
        <div class="face">
          <div class="graphic-box">
            <svg viewBox="0 0 100 90">
              <defs>
                <linearGradient id="silverGrad" x1="0" y1="0" x2="1" y2="1">
                  <stop offset="0%" stop-color="#ffffff"/>
                  <stop offset="50%" stop-color="#cbd5e1"/>
                  <stop offset="100%" stop-color="#94a3b8"/>
                </linearGradient>
                <linearGradient id="tarnishGrad" x1="0" y1="0" x2="1" y2="1">
                  <stop offset="0%" stop-color="#475569"/>
                  <stop offset="60%" stop-color="#1e293b"/>
                  <stop offset="100%" stop-color="#0f172a"/>
                </linearGradient>
              </defs>
              
              <g transform="translate(50, 45) rotate(-35) translate(-50, -45)">
                
                <path d="M 48 30 L 48 82 Q 48 85 50 85 Q 52 85 52 82 L 52 30 Z" fill="#94a3b8" stroke="#64748b" stroke-width="1" />
                
                <path d="M 50 8 C 41 8 40 22 49 32 L 50 32 Z" fill="url(#silverGrad)" stroke="#64748b" stroke-width="1" />
                
                <path d="M 50 8 C 59 8 60 22 51 32 L 50 32 Z" fill="url(#tarnishGrad)" stroke="#334155" stroke-width="1" />
                
                <path d="M 38 12 L 40 16 L 44 18 L 40 20 L 38 24 L 36 20 L 32 18 L 36 16 Z" fill="#f8fafc" opacity="0.9" />
                
                <circle cx="56" cy="20" r="1.5" fill="#fbbf24" />
                <circle cx="58" cy="25" r="1.2" fill="#fbbf24" />
              </g>
              <text x="24" y="80" font-size="9" font-weight="700" fill="#64748b">Shiny</text>
              <text x="50" y="80" font-size="9" font-weight="700" fill="#7c3aed">→</text>
              <text x="76" y="80" font-size="9" font-weight="700" fill="#334155">Tarnish</text>
            </svg>
          </div>
          <div class="card-label">
            <span class="card-num badge-color">2</span>
            <span>Color Change</span>
          </div>
        </div>
        <div class="face face-back" style="border-top: 4px solid #7c3aed;">
          <div class="back-title" style="color: #7c3aed;">Color Change</div>
          <div class="back-text">Shiny silver reacts with sulfur in the air to create a brand-new dark coating called tarnish.</div>
          <div class="back-tap-hint">tap to flip back</div>
        </div>
      </div>
    </div>

    
    <div class="card-wrap" tabindex="0" role="button" aria-label="Energy Light and Heat evidence card">
      <div class="card-inner">
        <div class="face">
          <div class="graphic-box">
            <svg viewBox="0 0 100 90">
              
              <circle class="glow-ring" cx="50" cy="48" r="28" fill="#ffedd5" />
              <circle class="glow-ring" cx="50" cy="48" r="20" fill="#fed7aa" />
              
              <rect x="26" y="66" width="48" height="9" rx="4.5" fill="#78350f" transform="rotate(-12 50 70)" />
              <rect x="26" y="66" width="48" height="9" rx="4.5" fill="#92400e" transform="rotate(12 50 70)" />
              
              <path class="flame-core" d="M 50 18 C 36 34 32 50 38 66 C 44 68 56 68 62 66 C 68 50 64 34 50 18 Z" fill="#ea580c" />
              
              <path class="flame-core" d="M 50 28 C 40 40 38 52 42 64 C 47 66 53 66 58 64 C 62 52 60 40 50 28 Z" fill="#facc15" />
              
              <path class="flame-core" d="M 50 42 C 45 48 44 56 46 62 C 48 63 52 63 54 62 C 56 56 55 48 50 42 Z" fill="#ffffff" />
              
              <circle cx="36" cy="30" r="1.5" fill="#f97316" opacity="0.8" />
              <circle cx="63" cy="26" r="1.8" fill="#facc15" opacity="0.8" />
              <circle cx="50" cy="12" r="1.5" fill="#ea580c" opacity="0.9" />
            </svg>
          </div>
          <div class="card-label">
            <span class="card-num badge-energy">3</span>
            <span>Heat & Light</span>
          </div>
        </div>
        <div class="face face-back" style="border-top: 4px solid #ea580c;">
          <div class="back-title" style="color: #ea580c;">Energy Release</div>
          <div class="back-text">Combustion breaks and reforms chemical bonds, releasing energy as bright light and heat.</div>
          <div class="back-tap-hint">tap to flip back</div>
        </div>
      </div>
    </div>

    
    <div class="card-wrap" tabindex="0" role="button" aria-label="Precipitate Formation evidence card">
      <div class="card-inner">
        <div class="face">
          <div class="graphic-box">
            <svg viewBox="0 0 100 90">
              
              <path d="M 36 12 L 44 24" stroke="#0d9488" stroke-width="2" stroke-linecap="round" />
              <path d="M 64 12 L 56 24" stroke="#0d9488" stroke-width="2" stroke-linecap="round" />
              <text x="50" y="16" font-size="8" font-weight="700" fill="#0d9488" text-anchor="middle">2 Liquids</text>
              
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              <path d="M 38 74 A 12 12 0 0 0 62 74 Z" fill="#f0fdfa" stroke="#0d9488" stroke-width="2" />
              
              <rect x="39" y="38" width="22" height="24" fill="#ccfbf1" opacity="0.6" />
              
              <rect x="39" y="56" width="22" height="12" fill="#5eead4" opacity="0.7" />
              
              <circle class="precip-p1" cx="45" cy="54" r="1.8" fill="#115e59" />
              <circle class="precip-p2" cx="54" cy="50" r="2.2" fill="#0f766e" />
              <circle class="precip-p3" cx="49" cy="58" r="1.6" fill="#134e4a" />
              
              <path d="M 39 72 A 11 11 0 0 0 61 72 Z" fill="#0f766e" />
              
              <text x="50" y="86" font-size="8" font-weight="700" fill="#0f766e" text-anchor="middle">Solid Settles</text>
            </svg>
          </div>
          <div class="card-label">
            <span class="card-num badge-precip">4</span>
            <span>Precipitate</span>
          </div>
        </div>
        <div class="face face-back" style="border-top: 4px solid #0d9488;">
          <div class="back-title" style="color: #0d9488;">Precipitate</div>
          <div class="back-text">Mixing two clear solutions forms a brand-new insoluble solid that settles at the bottom.</div>
          <div class="back-tap-hint">tap to flip back</div>
        </div>
      </div>
    </div>

  </div>

  <script>
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      };
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        if (e.key === 'Enter' || e.key === ' ') {
          e.preventDefault();
          toggle();
        }
      });
    });
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
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      justify-content: space-between;
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      user-select: none;
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    .selector-bar {
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      flex-wrap: wrap;
      gap: 6px;
      justify-content: center;
      width: 100%;
      max-width: 600px;
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    .btn-chip {
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      font-weight: 600;
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      gap: 5px;
      transition: all 0.25s ease;
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      background: #e2e8f0;
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      box-shadow: 0 2px 8px rgba(30, 41, 69, 0.25);
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    .tree-container {
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    @keyframes dash {
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    .node {
      position: relative;
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      border-radius: 12px;
      text-align: center;
      transition: all 0.3s ease;
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    /* Root Question Node */
    .root-node {
      background: #f8fafc;
      border: 2px solid #94a3b8;
      padding: 10px 16px;
      max-width: 320px;
      box-shadow: 0 2px 6px rgba(0,0,0,0.04);
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      font-size: 14px;
      font-weight: 700;
      color: #0f172a;
      line-height: 1.25;
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    /* Branch Decisions (NO / YES) */
    .branch-labels {
      position: absolute;
      top: 108px;
      width: 100%;
      max-width: 460px;
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      justify-content: space-between;
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      z-index: 2;
      pointer-events: none;
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      font-size: 12px;
      font-weight: 800;
      padding: 3px 10px;
      border-radius: 12px;
      background: #ffffff;
      border: 2px solid #cbd5e1;
      color: #64748b;
      transition: all 0.3s ease;
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    .branch-pill.active-no {
      border-color: #0284c7;
      background: #e0f2fe;
      color: #0369a1;
      box-shadow: 0 0 10px rgba(2, 132, 199, 0.3);
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      border-color: #16a34a;
      background: #dcfce7;
      color: #15803d;
      box-shadow: 0 0 10px rgba(22, 163, 74, 0.3);
    }

    /* Bottom Result Cards */
    .outcomes {
      display: flex;
      width: 100%;
      justify-content: space-between;
      gap: 12px;
      z-index: 2;
    }

    .outcome-card {
      flex: 1;
      border-radius: 12px;
      padding: 12px 10px;
      background: #ffffff;
      border: 2px solid #e2e8f0;
      transition: all 0.3s ease;
      opacity: 0.75;
    }
    .outcome-card.active {
      opacity: 1;
      transform: translateY(-2px);
    }
    .outcome-card.active-physical {
      border-color: #0284c7;
      box-shadow: 0 4px 14px rgba(2, 132, 199, 0.2);
      background: #f0f9ff;
    }
    .outcome-card.active-chemical {
      border-color: #16a34a;
      box-shadow: 0 4px 14px rgba(22, 163, 74, 0.2);
      background: #f0fdf4;
    }

    .badge-title {
      font-size: 15px;
      font-weight: 800;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      margin-bottom: 6px;
    }
    .physical-title { color: #0284c7; }
    .chemical-title { color: #16a34a; }

    .outcome-desc {
      font-size: 11px;
      font-weight: 600;
      color: #64748b;
      margin-bottom: 6px;
      text-transform: uppercase;
      letter-spacing: 0.3px;
    }

    .example-tag-list {
      display: flex;
      flex-wrap: wrap;
      gap: 4px;
      justify-content: center;
    }
    .mini-tag {
      font-size: 11px;
      padding: 2px 7px;
      background: rgba(0, 0, 0, 0.05);
      border-radius: 6px;
      color: #334155;
    }
    .mini-tag.highlight {
      background: #1e2945;
      color: #ffffff;
      font-weight: 700;
    }
  </style>
</head>
<body>

  
  <div class="selector-bar" id="chips">
    <button class="btn-chip" data-type="phys" data-tag="Melting butter">🧈 Melting butter</button>
    <button class="btn-chip" data-type="chem" data-tag="Baking bread">🍞 Baking bread</button>
    <button class="btn-chip" data-type="phys" data-tag="Cutting hair">✂️ Cutting hair</button>
    <button class="btn-chip" data-type="chem" data-tag="Fireworks exploding">🎆 Fireworks</button>
    <button class="btn-chip" data-type="phys" data-tag="Crushing chalk">🔨 Crushing chalk</button>
    <button class="btn-chip" data-type="chem" data-tag="Milk souring">🥛 Souring milk</button>
  </div>

  
  <div class="tree-container">
    
    <svg class="tree-lines" viewBox="0 0 540 320" preserveAspectRatio="none">
      <path id="pathLeft" class="tree-line" d="M 270 65 L 270 85 Q 270 120 135 120 L 135 190" />
      <path id="pathRight" class="tree-line" d="M 270 65 L 270 85 Q 270 120 405 120 L 405 190" />
    </svg>

    
    <div class="node root-node" id="rootNode">
      <div class="label">Ask this question</div>
      <div class="question">Brand NEW substance formed?</div>
    </div>

    
    <div class="branch-labels">
      <div class="branch-pill" id="pillNo">NO → Same Stuff</div>
      <div class="branch-pill" id="pillYes">YES → New Molecule</div>
    </div>

    
    <div class="outcomes">
      
      <div class="node outcome-card" id="cardPhys">
        <div class="badge-title physical-title">
          <span>💧</span> Physical Change
        </div>
        <div class="outcome-desc">Reversible / Shape Change</div>
        <div class="example-tag-list">
          <span class="mini-tag" id="tag-Melting butter">Melting butter</span>
          <span class="mini-tag" id="tag-Cutting hair">Cutting hair</span>
          <span class="mini-tag" id="tag-Crushing chalk">Crushing chalk</span>
        </div>
      </div>

      
      <div class="node outcome-card" id="cardChem">
        <div class="badge-title chemical-title">
          <span>🔥</span> Chemical Change
        </div>
        <div class="outcome-desc">New chemical properties</div>
        <div class="example-tag-list">
          <span class="mini-tag" id="tag-Baking bread">Baking bread</span>
          <span class="mini-tag" id="tag-Fireworks exploding">Fireworks</span>
          <span class="mini-tag" id="tag-Milk souring">Milk souring</span>
        </div>
      </div>
    </div>
  </div>

  <script>
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    const pathLeft = document.getElementById('pathLeft');
    const pathRight = document.getElementById('pathRight');
    const pillNo = document.getElementById('pillNo');
    const pillYes = document.getElementById('pillYes');
    const cardPhys = document.getElementById('cardPhys');
    const cardChem = document.getElementById('cardChem');
    const allTags = document.querySelectorAll('.mini-tag');

    function selectExample(btn) {
      // Toggle button states
      buttons.forEach(b => b.classList.remove('active'));
      btn.classList.add('active');

      const isChem = btn.dataset.type === 'chem';
      const targetTag = btn.dataset.tag;

      // Update Path & Pill Highlights
      if (isChem) {
        pathRight.className.baseVal = 'tree-line active-right';
        pathLeft.className.baseVal = 'tree-line';
        pillYes.className = 'branch-pill active-yes';
        pillNo.className = 'branch-pill';

        cardChem.className = 'node outcome-card active active-chemical';
        cardPhys.className = 'node outcome-card';
      } else {
        pathLeft.className.baseVal = 'tree-line active-left';
        pathRight.className.baseVal = 'tree-line';
        pillNo.className = 'branch-pill active-no';
        pillYes.className = 'branch-pill';

        cardPhys.className = 'node outcome-card active active-physical';
        cardChem.className = 'node outcome-card';
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    buttons.forEach(btn => {
      btn.addEventListener('click', () => selectExample(btn));
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    // Initial state: first button active
    selectExample(buttons[0]);
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      width: 100%;
      min-height: 100%;
      background: #f8f9fa;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 12px;
      gap: 10px;
      user-select: none;
    }

    /* Controls */
    .controls {
      display: flex;
      gap: 8px;
      width: 100%;
      max-width: 440px;
      justify-content: center;
    }
    .btn {
      flex: 1;
      padding: 6px 12px;
      font-size: 13px;
      font-weight: 600;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #64748b;
      border-radius: 20px;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      transition: background 0.2s, color 0.2s, border-color 0.2s, box-shadow 0.2s;
    }
    .btn.active {
      background: #22b7ff;
      border-color: #22b7ff;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(34, 183, 255, 0.35);
    }

    /* Comparison Stage */
    .stage {
      display: flex;
      width: 100%;
      max-width: 540px;
      align-items: center;
      justify-content: center;
      gap: 8px;
    }
    .panel {
      flex: 1;
      min-width: 0;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      border-radius: 12px;
      background: #ffffff;
      border: 2px solid #e2e8f0;
      padding: 8px 6px;
      box-shadow: 0 2px 8px rgba(0,0,0,0.04);
      transition: border-color 0.3s, box-shadow 0.3s;
    }
    .panel.highlight {
      border-color: #22b7ff;
      box-shadow: 0 0 0 2px rgba(34, 183, 255, 0.25);
    }
    .panel-header {
      font-size: 13px;
      font-weight: 700;
      display: flex;
      align-items: center;
      gap: 4px;
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    .temp {
      font-size: 11px;
      font-weight: 600;
      color: #64748b;
      background: #f1f5f9;
      padding: 1px 6px;
      border-radius: 10px;
    }

    .canvas-box {
      width: 100%;
      aspect-ratio: 1 / 1;
      max-height: 190px;
      background: #f0f9ff;
      border-radius: 8px;
      overflow: hidden;
      position: relative;
    }
    canvas {
      width: 100%;
      height: 100%;
      display: block;
    }

    /* Center Arrow */
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      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 2px;
      min-width: 48px;
      font-size: 10px;
      font-weight: 700;
      color: #64748b;
      text-align: center;
      line-height: 1.1;
    }
    .arrow-icon {
      font-size: 18px;
      color: #22b7ff;
    }

    /* Bottom Summary Badge */
    .footer-badge {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      padding: 6px 14px;
      border-radius: 20px;
      font-size: 12px;
      font-weight: 600;
      color: #1e2945;
      text-align: center;
      box-shadow: 0 1px 4px rgba(0,0,0,0.03);
    }
    .footer-badge span {
      color: #0284c7;
    }

    @media (max-width: 380px) {
      .panel-header { font-size: 11px; }
      .temp { font-size: 10px; padding: 0 4px; }
      .arrow-divider { min-width: 36px; font-size: 9px; }
      .arrow-icon { font-size: 14px; }
      .footer-badge { font-size: 11px; padding: 5px 10px; }
      .btn { font-size: 12px; padding: 5px 8px; }
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button class="btn active" id="btnBoth">All States</button>
    <button class="btn" id="btnSolid">Solid Ice</button>
    <button class="btn" id="btnLiquid">Liquid Water</button>
  </div>

  
  <div class="stage">
    
    <div class="panel" id="panelSolid">
      <div class="panel-header">
        <span>Ice</span>
        <span class="temp">0°C</span>
      </div>
      <div class="canvas-box">
        <canvas id="canvasSolid"></canvas>
      </div>
    </div>

    
    <div class="arrow-divider">
      <span style="color:#ef4444;">+ Heat</span>
      <div class="arrow-icon">⇄</div>
      <span style="color:#0284c7;">- Heat</span>
    </div>

    
    <div class="panel" id="panelLiquid">
      <div class="panel-header">
        <span>Water</span>
        <span class="temp">20°C</span>
      </div>
      <div class="canvas-box">
        <canvas id="canvasLiquid"></canvas>
      </div>
    </div>
  </div>

  
  <div class="footer-badge">
    Same molecules (<span>H₂O</span>) — only spacing &amp; motion changed!
  </div>

  <script>
    const cvsSolid = document.getElementById('canvasSolid');
    const ctxSolid = cvsSolid.getContext('2d');
    const cvsLiquid = document.getElementById('canvasLiquid');
    const ctxLiquid = cvsLiquid.getContext('2d');

    const btnBoth = document.getElementById('btnBoth');
    const btnSolid = document.getElementById('btnSolid');
    const btnLiquid = document.getElementById('btnLiquid');
    const panelSolid = document.getElementById('panelSolid');
    const panelLiquid = document.getElementById('panelLiquid');

    let mode = 'both'; // 'both' | 'solid' | 'liquid'

    function setMode(m) {
      mode = m;
      btnBoth.classList.toggle('active', m === 'both');
      btnSolid.classList.toggle('active', m === 'solid');
      btnLiquid.classList.toggle('active', m === 'liquid');

      panelSolid.classList.toggle('highlight', m === 'solid');
      panelLiquid.classList.toggle('highlight', m === 'liquid');
    }

    btnBoth.onclick = () => setMode('both');
    btnSolid.onclick = () => setMode('solid');
    btnLiquid.onclick = () => setMode('liquid');

    // High-DPI Canvas Resizing
    let width = 180, height = 180;
    function resize() {
      const rect = cvsSolid.getBoundingClientRect();
      const dpr = window.devicePixelRatio || 1;
      width = rect.width;
      height = rect.height;

      [cvsSolid, cvsLiquid].forEach(cvs => {
        cvs.width = width * dpr;
        cvs.height = height * dpr;
        const ctx = cvs.getContext('2d');
        ctx.resetTransform();
        ctx.scale(dpr, dpr);
      });
      initLattices();
    }
    window.addEventListener('resize', resize);

    // Molecular Setup: 9 Molecules each (3x3)
    const COUNT = 9;
    let solidMols = [];
    let liquidMols = [];

    function initLattices() {
      solidMols = [];
      liquidMols = [];

      const rows = 3, cols = 3;
      const stepX = width / (cols + 1);
      const stepY = height / (rows + 1);

      let idx = 0;
      for (let r = 1; r <= rows; r++) {
        for (let c = 1; c <= cols; c++) {
          const baseX = c * stepX;
          const baseY = r * stepY;
          solidMols.push({
            baseX: baseX,
            baseY: baseY,
            angle: (idx % 2 === 0 ? 0.3 : -0.3) + (r * 0.4),
            phase: Math.random() * Math.PI * 2
          });

          liquidMols.push({
            x: baseX + (Math.random() - 0.5) * 15,
            y: baseY + (Math.random() - 0.5) * 15,
            vx: (Math.random() - 0.5) * 0.9,
            vy: (Math.random() - 0.5) * 0.9,
            angle: Math.random() * Math.PI * 2,
            vAngle: (Math.random() - 0.5) * 0.04
          });
          idx++;
        }
      }
    }

    // Draw single H2O Molecule
    function drawH2O(ctx, x, y, angle) {
      ctx.save();
      ctx.translate(x, y);
      ctx.rotate(angle);

      const rO = 7.5;   // Oxygen radius
      const rH = 4.5;   // Hydrogen radius
      const bondDist = 8.5; 
      const hAngle = 0.92; // ~105 degrees

      // 2 Hydrogen atoms (White with slate border)
      [-hAngle, hAngle].forEach(a => {
        const hx = Math.cos(Math.PI / 2 + a) * bondDist;
        const hy = Math.sin(Math.PI / 2 + a) * bondDist;

        ctx.beginPath();
        ctx.arc(hx, hy, rH, 0, Math.PI * 2);
        ctx.fillStyle = '#ffffff';
        ctx.fill();
        ctx.lineWidth = 1.2;
        ctx.strokeStyle = '#94a3b8';
        ctx.stroke();
      });

      // 1 Oxygen atom (Red)
      ctx.beginPath();
      ctx.arc(0, 0, rO, 0, Math.PI * 2);
      ctx.fillStyle = '#ef4444';
      ctx.fill();
      ctx.lineWidth = 1.2;
      ctx.strokeStyle = '#b91c1c';
      ctx.stroke();

      ctx.restore();
    }

    let time = 0;
    function animate() {
      time += 0.05;

      // Draw Solid Ice (Vibrating in lattice)
      ctxSolid.clearRect(0, 0, width, height);
      solidMols.forEach((m) => {
        // Small rapid vibration
        const vibAmp = 1.2;
        const vx = Math.sin(time * 6 + m.phase) * vibAmp;
        const vy = Math.cos(time * 5 + m.phase * 1.5) * vibAmp;
        const vAngle = Math.sin(time * 4 + m.phase) * 0.08;

        drawH2O(ctxSolid, m.baseX + vx, m.baseY + vy, m.angle + vAngle);
      });

      // Draw Liquid Water (Tumbling & Drifting smoothly)
      ctxLiquid.clearRect(0, 0, width, height);
      const pad = 12;
      liquidMols.forEach(m => {
        m.x += m.vx;
        m.y += m.vy;
        m.angle += m.vAngle;

        // Bounce gently off bounds
        if (m.x < pad) { m.x = pad; m.vx *= -1; }
        if (m.x > width - pad) { m.x = width - pad; m.vx *= -1; }
        if (m.y < pad) { m.y = pad; m.vy *= -1; }
        if (m.y > height - pad) { m.y = height - pad; m.vy *= -1; }

        drawH2O(ctxLiquid, m.x, m.y, m.angle);
      });

      requestAnimationFrame(animate);
    }

    resize();
    animate();
  </script>
</body>
</html>

OGS.7.PS.3

Aligned learning resources

Related diagrams