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Override for the tutor's lesson content generation calls. Auto uses the system default (Claude Sonnet 5 for lesson text, Opus 5 for diagrams).

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Tutoring abilities

Imagine walking up a "down" escalator at the exact same speed it moves down.

To someone watching from the side, you look completely still, even though intense motion is happening in both directions.

In chemistry, this balance is called **dynamic equilibrium**—a state in a sealed container where the forward and reverse reactions occur at the exact same rate.

<!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: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
      background: transparent;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      width: 100%;
      min-height: 100%;
      user-select: none;
      padding: 8px;
    }

    .main-stage {
      width: 100%;
      max-width: 480px;
      display: flex;
      flex-direction: column;
      gap: 10px;
    }

    /* Controls Bar */
    .controls {
      display: flex;
      justify-content: center;
      gap: 8px;
      width: 100%;
    }

    .btn {
      flex: 1;
      padding: 8px 10px;
      font-size: 13px;
      font-weight: 600;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      background: #ffffff;
      color: #475569;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      transition: background 0.2s, color 0.2s, box-shadow 0.2s;
    }

    .btn:hover {
      background: #f8fafc;
      box-shadow: 0 2px 4px rgba(0,0,0,0.05);
    }

    .btn.active {
      background: #22b7ff;
      color: #ffffff;
      border-color: #22b7ff;
    }

    /* Reaction Chamber Box */
    .chamber-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px;
      box-shadow: 0 4px 12px rgba(0,0,0,0.03);
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    .chamber-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      font-size: 14px;
      font-weight: 700;
    }

    .tag-a { color: #0284c7; }
    .tag-b { color: #d97706; }

    /* Canvas Area */
    .canvas-container {
      position: relative;
      width: 100%;
      height: 180px;
      background: #f8fafc;
      border-radius: 8px;
      border: 1px dashed #cbd5e1;
      overflow: hidden;
    }

    canvas {
      width: 100%;
      height: 100%;
      display: block;
    }

    /* Rate Meters */
    .rates-row {
      display: flex;
      gap: 12px;
      margin-top: 4px;
    }

    .rate-box {
      flex: 1;
      display: flex;
      flex-direction: column;
      gap: 4px;
    }

    .rate-label {
      display: flex;
      justify-content: space-between;
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
    }

    .meter-track {
      height: 8px;
      background: #e2e8f0;
      border-radius: 4px;
      overflow: hidden;
    }

    .meter-fill-forward {
      height: 100%;
      width: 50%;
      background: #0284c7;
      border-radius: 4px;
      transition: width 0.3s ease;
    }

    .meter-fill-reverse {
      height: 100%;
      width: 50%;
      background: #d97706;
      border-radius: 4px;
      transition: width 0.3s ease;
    }

    /* Status Badge */
    .status-badge {
      text-align: center;
      font-size: 12px;
      font-weight: 700;
      padding: 6px;
      border-radius: 6px;
      background: #f0fdf4;
      color: #166534;
      transition: background 0.3s, color 0.3s;
    }

    .status-badge.shifting {
      background: #fefce8;
      color: #854d0e;
    }
  </style>
</head>
<body>

<div class="main-stage">
  
  <div class="controls">
    <button class="btn active" id="btnEq">Equilibrium</button>
    <button class="btn" id="btnAddA">+ Reactant A</button>
    <button class="btn" id="btnAddB">+ Product B</button>
  </div>

  
  <div class="chamber-card">
    <div class="chamber-header">
      <span class="tag-a">Reactants (A)</span>
      <span style="color:#64748b; font-size:16px;">⇌</span>
      <span class="tag-b">Products (B)</span>
    </div>

    <div class="canvas-container">
      <canvas id="simCanvas"></canvas>
    </div>

    
    <div class="rates-row">
      <div class="rate-box">
        <div class="rate-label">
          <span>Forward Rate (→)</span>
          <span id="txtFwd">50%</span>
        </div>
        <div class="meter-track">
          <div class="meter-fill-forward" id="barFwd"></div>
        </div>
      </div>

      <div class="rate-box">
        <div class="rate-label">
          <span>Reverse Rate (←)</span>
          <span id="txtRev">50%</span>
        </div>
        <div class="meter-track">
          <div class="meter-fill-reverse" id="barRev"></div>
        </div>
      </div>
    </div>

    
    <div class="status-badge" id="statusBadge">
      Forward Rate = Reverse Rate
    </div>
  </div>
</div>

<script>
  const canvas = document.getElementById('simCanvas');
  const ctx = canvas.getContext('2d');
  const btnEq = document.getElementById('btnEq');
  const btnAddA = document.getElementById('btnAddA');
  const btnAddB = document.getElementById('btnAddB');
  const barFwd = document.getElementById('barFwd');
  const barRev = document.getElementById('barRev');
  const txtFwd = document.getElementById('txtFwd');
  const txtRev = document.getElementById('txtRev');
  const statusBadge = document.getElementById('statusBadge');

  let width, height;
  function resize() {
    width = canvas.width = canvas.parentElement.clientWidth;
    height = canvas.height = canvas.parentElement.clientHeight;
  }
  window.addEventListener('resize', resize);
  resize();

  class Particle {
    constructor(type, x, y) {
      this.type = type; // 'A' or 'B'
      this.x = x;
      this.y = y;
      this.vx = (Math.random() - 0.5) * 1.5;
      this.vy = (Math.random() - 0.5) * 1.5;
      this.radius = 5.5;
    }

    update() {
      this.x += this.vx;
      this.y += this.vy;

      // Bounce bounds
      if (this.x - this.radius < 0) { this.x = this.radius; this.vx *= -1; }
      if (this.x + this.radius > width) { this.x = width - this.radius; this.vx *= -1; }
      if (this.y - this.radius < 0) { this.y = this.radius; this.vy *= -1; }
      if (this.y + this.radius > height) { this.y = height - this.radius; this.vy *= -1; }

      // Prefer home region gently
      const mid = width / 2;
      if (this.type === 'A' && this.x > mid + 20) {
        this.vx -= 0.03;
      } else if (this.type === 'B' && this.x < mid - 20) {
        this.vx += 0.03;
      }
    }

    draw() {
      ctx.beginPath();
      ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2);
      ctx.fillStyle = this.type === 'A' ? '#0284c7' : '#d97706';
      ctx.fill();
    }
  }

  let particles = [];
  const BASE_COUNT = 14;

  function initEquilibrium() {
    particles = [];
    const mid = width / 2;
    for (let i = 0; i < BASE_COUNT; i++) {
      particles.push(new Particle('A', Math.random() * (mid - 30) + 15, Math.random() * (height - 30) + 15));
      particles.push(new Particle('B', mid + Math.random() * (mid - 30) + 15, Math.random() * (height - 30) + 15));
    }
  }
  initEquilibrium();

  function addReactantsA() {
    const mid = width / 2;
    for (let i = 0; i < 10; i++) {
      particles.push(new Particle('A', Math.random() * (mid - 30) + 15, Math.random() * (height - 30) + 15));
    }
  }

  function addProductsB() {
    const mid = width / 2;
    for (let i = 0; i < 10; i++) {
      particles.push(new Particle('B', mid + Math.random() * (mid - 30) + 15, Math.random() * (height - 30) + 15));
    }
  }

  function setMode(mode) {
    [btnEq, btnAddA, btnAddB].forEach(b => b.classList.remove('active'));
    if (mode === 'eq') {
      btnEq.classList.add('active');
      initEquilibrium();
    } else if (mode === 'addA') {
      btnAddA.classList.add('active');
      addReactantsA();
    } else if (mode === 'addB') {
      btnAddB.classList.add('active');
      addProductsB();
    }
  }

  btnEq.addEventListener('click', () => setMode('eq'));
  btnAddA.addEventListener('click', () => setMode('addA'));
  btnAddB.addEventListener('click', () => setMode('addB'));

  let fwdDisplay = 50;
  let revDisplay = 50;

  function loop() {
    ctx.clearRect(0, 0, width, height);

    // Center dividing line
    const mid = width / 2;
    ctx.strokeStyle = '#e2e8f0';
    ctx.lineWidth = 2;
    ctx.setLineDash([4, 4]);
    ctx.beginPath();
    ctx.moveTo(mid, 0);
    ctx.lineTo(mid, height);
    ctx.stroke();
    ctx.setLineDash([]);

    let countA = 0;
    let countB = 0;

    particles.forEach(p => {
      p.update();
      p.draw();
      if (p.type === 'A') countA++;
      else countB++;
    });

    // Probability of conversion based on concentration
    // Dynamic adjustment pushes back towards balance
    const kForward = 0.008;
    const kReverse = 0.008;

    particles.forEach(p => {
      if (p.type === 'A' && Math.random() < kForward) {
        p.type = 'B';
        p.vx += 0.8; // move right
      } else if (p.type === 'B' && Math.random() < kReverse) {
        p.type = 'A';
        p.vx -= 0.8; // move left
      }
    });

    // Calculate rates
    const rawFwd = countA * kForward * 400;
    const rawRev = countB * kReverse * 400;
    const total = (rawFwd + rawRev) || 1;

    const targetFwd = Math.round((rawFwd / total) * 100);
    const targetRev = 100 - targetFwd;

    fwdDisplay += (targetFwd - fwdDisplay) * 0.08;
    revDisplay += (targetRev - revDisplay) * 0.08;

    barFwd.style.width = fwdDisplay.toFixed(0) + '%';
    barRev.style.width = revDisplay.toFixed(0) + '%';
    txtFwd.textContent = fwdDisplay.toFixed(0) + '%';
    txtRev.textContent = revDisplay.toFixed(0) + '%';

    const diff = Math.abs(fwdDisplay - revDisplay);
    if (diff < 6) {
      statusBadge.textContent = 'Forward Rate = Reverse Rate';
      statusBadge.classList.remove('shifting');
    } else if (fwdDisplay > revDisplay) {
      statusBadge.textContent = 'Forward Rate > Reverse Rate (Shifting →)';
      statusBadge.classList.add('shifting');
    } else {
      statusBadge.textContent = 'Reverse Rate > Forward Rate (Shifting ←)';
      statusBadge.classList.add('shifting');
    }

    requestAnimationFrame(loop);
  }

  requestAnimationFrame(loop);
</script>

</body>
</html>

What happens if someone suddenly speeds up that escalator or drops extra weight onto one side of the reaction?

In 1884, French chemist Henri Le Chatelier wanted to understand how industrial chemical reactions respond when their conditions are disrupted.

He discovered that when a system at **dynamic equilibrium** is subjected to a change in conditions, the system shifts to **counteract** that change.

You can think of equilibrium like a chemical reflex: whatever you do to the system, the system responds by doing the exact opposite to restore balance.

<!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">
  <title>Le Chatelier's Principle</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      user-select: none;
      -webkit-user-select: none;
    }

    body {
      background: transparent;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px 8px;
      overflow-x: hidden;
    }

    /* Status Pill */
    .status-badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      padding: 6px 14px;
      border-radius: 20px;
      font-size: 14px;
      font-weight: 700;
      background: #f1f5f9;
      color: #475569;
      box-shadow: inset 0 0 0 1px #e2e8f0;
      transition: all 0.4s ease;
      min-height: 32px;
    }

    .status-badge.shift-right {
      background: #eff6ff;
      color: #0284c7;
      box-shadow: inset 0 0 0 1px #bae6fd;
    }

    .status-badge.shift-left {
      background: #fefce8;
      color: #ca8a04;
      box-shadow: inset 0 0 0 1px #fef08a;
    }

    .status-badge.balanced {
      background: #ecfdf5;
      color: #059669;
      box-shadow: inset 0 0 0 1px #a7f3d0;
    }

    /* Balance Stage */
    .stage {
      position: relative;
      width: 100%;
      max-width: 440px;
      height: 200px;
      display: flex;
      align-items: center;
      justify-content: center;
      margin: 8px 0;
    }

    /* Central Fulcrum */
    .fulcrum {
      position: absolute;
      bottom: 24px;
      left: 50%;
      transform: translateX(-50%);
      width: 0;
      height: 0;
      border-left: 20px solid transparent;
      border-right: 20px solid transparent;
      border-bottom: 38px solid #94a3b8;
      z-index: 1;
    }

    .fulcrum-base {
      position: absolute;
      bottom: 18px;
      left: 50%;
      transform: translateX(-50%);
      width: 80px;
      height: 8px;
      background: #cbd5e1;
      border-radius: 4px;
    }

    /* Beam */
    .beam-wrapper {
      position: absolute;
      bottom: 58px;
      left: 50%;
      width: 320px;
      height: 12px;
      transform-origin: center center;
      transform: translateX(-50%) rotate(0deg);
      transition: transform 0.6s cubic-bezier(0.34, 1.56, 0.64, 1);
      z-index: 2;
    }

    .beam {
      width: 100%;
      height: 8px;
      background: #475569;
      border-radius: 4px;
      position: relative;
    }

    .pivot-dot {
      position: absolute;
      top: 50%;
      left: 50%;
      transform: translate(-50%, -50%);
      width: 14px;
      height: 14px;
      background: #1e2945;
      border: 2px solid #ffffff;
      border-radius: 50%;
    }

    /* Reaction Pan / Containers */
    .pan {
      position: absolute;
      top: -65px;
      width: 100px;
      height: 70px;
      background: #ffffff;
      border: 2px solid #e2e8f0;
      border-radius: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: flex-end;
      padding: 6px;
      box-shadow: 0 4px 6px -1px rgba(0,0,0,0.06);
      transition: border-color 0.3s, transform 0.6s cubic-bezier(0.34, 1.56, 0.64, 1);
    }

    .pan-left {
      left: 0;
      transform-origin: center bottom;
    }

    .pan-right {
      right: 0;
      transform-origin: center bottom;
    }

    .pan-label {
      font-size: 13px;
      font-weight: 700;
      margin-top: 4px;
      letter-spacing: -0.2px;
    }

    .pan-left .pan-label { color: #0284c7; }
    .pan-right .pan-label { color: #d97706; }

    /* Molecules Grid */
    .molecules {
      display: flex;
      flex-wrap: wrap;
      gap: 4px;
      justify-content: center;
      align-content: flex-end;
      width: 100%;
      height: 38px;
    }

    .mol {
      width: 12px;
      height: 12px;
      border-radius: 50%;
      transition: all 0.4s ease;
    }

    .mol-blue {
      background: #0284c7;
      box-shadow: 0 1px 3px rgba(2, 132, 199, 0.4);
    }

    .mol-amber {
      background: #f59e0b;
      box-shadow: 0 1px 3px rgba(245, 158, 11, 0.4);
    }

    /* Central Rate Flow Arrows */
    .rate-flow {
      position: absolute;
      top: 25px;
      left: 50%;
      transform: translateX(-50%);
      display: flex;
      flex-direction: column;
      gap: 4px;
      align-items: center;
      z-index: 3;
    }

    .flow-arrow {
      display: flex;
      align-items: center;
      font-size: 15px;
      font-weight: 800;
      opacity: 0.25;
      transition: all 0.4s ease;
    }

    .flow-forward { color: #0284c7; }
    .flow-reverse { color: #d97706; }

    .flow-active {
      opacity: 1;
      transform: scale(1.2);
    }

    /* Interactive Controls */
    .controls {
      display: flex;
      gap: 8px;
      width: 100%;
      max-width: 360px;
      justify-content: center;
      flex-wrap: wrap;
      z-index: 10;
    }

    .btn {
      flex: 1;
      min-width: 100px;
      padding: 10px 12px;
      border-radius: 10px;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #1e2945;
      font-size: 14px;
      font-weight: 600;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      box-shadow: 0 1px 2px rgba(0,0,0,0.05);
      transition: background 0.2s, border-color 0.2s, box-shadow 0.2s;
    }

    .btn:active {
      background: #f1f5f9;
    }

    .btn.active {
      border-color: #0284c7;
      background: #f0f9ff;
      color: #0284c7;
      box-shadow: 0 0 0 1px #0284c7;
    }

    .btn-reset {
      flex: 0 0 auto;
      min-width: 44px;
      padding: 10px 14px;
    }
  </style>
</head>
<body>

  
  <div id="statusBadge" class="status-badge balanced">
    <span id="statusIcon">⚖️</span>
    <span id="statusText">Equilibrium</span>
  </div>

  
  <div class="stage">
    
    <div class="rate-flow">
      <div id="forwardArrow" class="flow-arrow flow-forward">⟶</div>
      <div id="reverseArrow" class="flow-arrow flow-reverse">⟵</div>
    </div>

    
    <div id="beamWrapper" class="beam-wrapper">
      <div class="beam">
        <div class="pivot-dot"></div>

        
        <div id="panLeft" class="pan pan-left">
          <div id="reactantsMol" class="molecules"></div>
          <span class="pan-label">Reactants</span>
        </div>

        
        <div id="panRight" class="pan pan-right">
          <div id="productsMol" class="molecules"></div>
          <span class="pan-label">Products</span>
        </div>
      </div>
    </div>

    
    <div class="fulcrum"></div>
    <div class="fulcrum-base"></div>
  </div>

  
  <div class="controls">
    <button id="addReactantsBtn" class="btn" onclick="disturb('reactants')">
      + Reactants
    </button>
    <button id="addProductsBtn" class="btn" onclick="disturb('products')">
      + Products
    </button>
    <button id="resetBtn" class="btn btn-reset" onclick="resetSystem()" title="Reset">
      ↺
    </button>
  </div>

  <script>
    let state = 'balanced'; // 'balanced', 'adding-r', 'shifting-r', 'adding-p', 'shifting-p'
    let timeouts = [];

    const beamWrapper = document.getElementById('beamWrapper');
    const panLeft = document.getElementById('panLeft');
    const panRight = document.getElementById('panRight');
    const reactantsMol = document.getElementById('reactantsMol');
    const productsMol = document.getElementById('productsMol');
    const statusBadge = document.getElementById('statusBadge');
    const statusIcon = document.getElementById('statusIcon');
    const statusText = document.getElementById('statusText');
    const forwardArrow = document.getElementById('forwardArrow');
    const reverseArrow = document.getElementById('reverseArrow');
    const btnR = document.getElementById('addReactantsBtn');
    const btnP = document.getElementById('addProductsBtn');

    function renderMolecules(rCount, pCount) {
      reactantsMol.innerHTML = '';
      for (let i = 0; i < rCount; i++) {
        const d = document.createElement('div');
        d.className = 'mol mol-blue';
        reactantsMol.appendChild(d);
      }
      productsMol.innerHTML = '';
      for (let i = 0; i < pCount; i++) {
        const d = document.createElement('div');
        d.className = 'mol mol-amber';
        productsMol.appendChild(d);
      }
    }

    function clearAllTimeouts() {
      timeouts.forEach(t => clearTimeout(t));
      timeouts = [];
    }

    function resetSystem() {
      clearAllTimeouts();
      btnR.classList.remove('active');
      btnP.classList.remove('active');

      // Reset beam tilt
      beamWrapper.style.transform = 'translateX(-50%) rotate(0deg)';
      panLeft.style.transform = 'rotate(0deg)';
      panRight.style.transform = 'rotate(0deg)';

      // Molecules count
      renderMolecules(4, 4);

      // Arrows
      forwardArrow.classList.remove('flow-active');
      reverseArrow.classList.remove('flow-active');

      // Status
      statusBadge.className = 'status-badge balanced';
      statusIcon.textContent = '⚖️';
      statusText.textContent = 'Equilibrium';
    }

    function disturb(type) {
      clearAllTimeouts();
      btnR.classList.toggle('active', type === 'reactants');
      btnP.classList.toggle('active', type === 'products');

      if (type === 'reactants') {
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Why does this happen? A disturbance changes the rate of either the forward or reverse reaction, forcing the faster reaction to run until both rates match again.

How does this rule let us predict what a real chemical reaction will do?

Consider a simple reversible reaction at dynamic equilibrium: $$\text{A} \rightleftharpoons \text{B}$$

If you suddenly inject extra substance $\text{A}$, the system counteracts this addition by using up the excess $\text{A}$, shifting the **position of equilibrium** to the right to form more $\text{B}$.

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A common mistake is assuming the system completely cancels out the change you made.

The system only **partially counteracts** the change—if you add 10 moles of $\text{A}$, the system converts some of it to $\text{B}$, but the final amount of $\text{A}$ is still higher than where you started.

With this foundational rule in hand, we can now predict how changes in concentration, gas pressure, and temperature shift any chemical equilibrium.

science

Introduction to Le Chatelier's Principle. State Le Chatelier's principle: when a system at dynamic equilibrium is subjected to a change in conditions, the system shifts to counteract that change.

Reversible Reactions and Equilibrium - GCSE Chemistry (AQA / Edexcel / OCR)

Factors Affecting Equilibrium and Le Chatelier's Principle (Key Stage 4)

Le Chatelier's Principle & Changing Conditions Revision Notes

When introducing Le Chatelier's Principle to GCSE students, emphasize the 'Opposition / Counteraction Heuristic': train students to follow a 4-step answering structure for exam success: (1) Identify the change, (2) State what the system does to oppose the change, (3) State which way the equilibrium shifts (left or right), and (4) Conclude the effect on product/reactant amounts. Explicitly contrast 'rates' with 'equilibrium position' to prevent conflation, and use particle diagrams to reinforce mole-counting rules for pressure effects.

Introduction to Le Chatelier's Principle

Le Chatelier's Principle

Applying the Principle