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Every time an oil refinery separates crude oil, it ends up with a giant surplus of thick, gooey residue that few people want, while facing a constant shortage of light fuels like gasoline.

Crude oil is a mixture of **hydrocarbons**—compounds made solely of hydrogen and carbon atoms—separated by fractional distillation into fractions of varying chain lengths.

<!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;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      background: #ffffff;
      color: #1e2945;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .chart-container {
      width: 100%;
      max-width: 540px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }

    .callout {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 8px 12px;
      text-align: center;
      font-size: 14px;
      font-weight: 600;
      color: #1e2945;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
    }

    .badge-deficit {
      background: #fee2e2;
      color: #b91c1c;
      padding: 2px 6px;
      border-radius: 4px;
      font-size: 12px;
      font-weight: 700;
    }

    .badge-surplus {
      background: #e0f2fe;
      color: #0369a1;
      padding: 2px 6px;
      border-radius: 4px;
      font-size: 12px;
      font-weight: 700;
    }

    .bars-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 16px;
      background: #ffffff;
      border: 1px solid #e6e6e6;
      border-radius: 12px;
      padding: 16px 12px 12px 12px;
    }

    .column-section {
      display: flex;
      flex-direction: column;
      align-items: center;
    }

    .column-title {
      font-size: 15px;
      font-weight: 700;
      margin-bottom: 12px;
      color: #1e2945;
      text-align: center;
    }

    .bars-area {
      height: 200px;
      width: 100%;
      display: flex;
      align-items: flex-end;
      justify-content: space-around;
      border-bottom: 2px solid #cbd5e1;
      padding-bottom: 2px;
      position: relative;
    }

    .bar-wrapper {
      display: flex;
      flex-direction: column;
      align-items: center;
      width: 40%;
      height: 100%;
      justify-content: flex-end;
      cursor: pointer;
    }

    .bar-val {
      font-size: 13px;
      font-weight: 700;
      margin-bottom: 4px;
      color: #1e2945;
    }

    .bar {
      width: 100%;
      border-radius: 6px 6px 0 0;
      transition: height 0.4s ease, opacity 0.3s ease, transform 0.2s ease;
    }

    .bar-petrol {
      background: #f59e0b;
    }

    .bar-fueloil {
      background: #475569;
    }

    .bar-label {
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      margin-top: 8px;
      text-align: center;
      line-height: 1.2;
    }

    .legend {
      display: flex;
      justify-content: center;
      gap: 16px;
      margin-top: 4px;
    }

    .legend-item {
      display: flex;
      align-items: center;
      gap: 6px;
      font-size: 13px;
      font-weight: 500;
      color: #475569;
    }

    .legend-dot {
      width: 12px;
      height: 12px;
      border-radius: 3px;
    }

    .controls {
      display: flex;
      justify-content: center;
      gap: 8px;
    }

    .filter-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      padding: 6px 12px;
      border-radius: 6px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      transition: background 0.2s ease, border-color 0.2s ease;
    }

    .filter-btn.active {
      background: #22b7ff;
      border-color: #0284c7;
      color: #ffffff;
    }

    .dimmed {
      opacity: 0.25;
    }
  </style>
</head>
<body>

<div class="chart-container">
  <div class="callout" id="calloutText">
    <span>Petrol:</span> <span class="badge-deficit">Deficit (-25%)</span>
    <span style="margin: 0 4px; color:#cbd5e1;">|</span>
    <span>Fuel Oil:</span> <span class="badge-surplus">Surplus (+35%)</span>
  </div>

  <div class="bars-grid">
    
    <div class="column-section">
      <div class="column-title">Supply from Crude Oil</div>
      <div class="bars-area">
        <div class="bar-wrapper" id="supply-petrol">
          <span class="bar-val">20%</span>
          <div class="bar bar-petrol" style="height: 40%;"></div>
          <span class="bar-label">Petrol</span>
        </div>
        <div class="bar-wrapper" id="supply-fueloil">
          <span class="bar-val">50%</span>
          <div class="bar bar-fueloil" style="height: 100%;"></div>
          <span class="bar-label">Fuel Oil</span>
        </div>
      </div>
    </div>

    
    <div class="column-section">
      <div class="column-title">Market Demand</div>
      <div class="bars-area">
        <div class="bar-wrapper" id="demand-petrol">
          <span class="bar-val">45%</span>
          <div class="bar bar-petrol" style="height: 90%;"></div>
          <span class="bar-label">Petrol</span>
        </div>
        <div class="bar-wrapper" id="demand-fueloil">
          <span class="bar-val">15%</span>
          <div class="bar bar-fueloil" style="height: 30%;"></div>
          <span class="bar-label">Fuel Oil</span>
        </div>
      </div>
    </div>
  </div>

  
  <div class="controls">
    <button class="filter-btn active" id="btn-all">All Fractions</button>
    <button class="filter-btn" id="btn-petrol">Petrol (Short-chain)</button>
    <button class="filter-btn" id="btn-fueloil">Fuel Oil (Long-chain)</button>
  </div>
</div>

<script>
  const btnAll = document.getElementById('btn-all');
  const btnPetrol = document.getElementById('btn-petrol');
  const btnFuelOil = document.getElementById('btn-fueloil');

  const supplyPetrol = document.getElementById('supply-petrol');
  const demandPetrol = document.getElementById('demand-petrol');
  const supplyFuelOil = document.getElementById('supply-fueloil');
  const demandFuelOil = document.getElementById('demand-fueloil');

  const callout = document.getElementById('calloutText');

  function setMode(mode) {
    btnAll.classList.remove('active');
    btnPetrol.classList.remove('active');
    btnFuelOil.classList.remove('active');

    supplyPetrol.classList.remove('dimmed');
    demandPetrol.classList.remove('dimmed');
    supplyFuelOil.classList.remove('dimmed');
    demandFuelOil.classList.remove('dimmed');

    if (mode === 'all') {
      btnAll.classList.add('active');
      callout.innerHTML = `<span>Petrol:</span> <span class="badge-deficit">Deficit (-25%)</span>
        <span style="margin: 0 4px; color:#cbd5e1;">|</span>
        <span>Fuel Oil:</span> <span class="badge-surplus">Surplus (+35%)</span>`;
    } else if (mode === 'petrol') {
      btnPetrol.classList.add('active');
      supplyFuelOil.classList.add('dimmed');
      demandFuelOil.classList.add('dimmed');
      callout.innerHTML = `<span>Petrol (Short Chain):</span> <span class="badge-deficit">High Demand Deficit</span>`;
    } else if (mode === 'fueloil') {
      btnFuelOil.classList.add('active');
      supplyPetrol.classList.add('dimmed');
      demandPetrol.classList.add('dimmed');
      callout.innerHTML = `<span>Fuel Oil (Long Chain):</span> <span class="badge-surplus">Unwanted Surplus</span>`;
    }
  }

  btnAll.addEventListener('click', () => setMode('all'));
  btnPetrol.addEventListener('click', () => setMode('petrol'));
  btnFuelOil.addEventListener('click', () => setMode('fueloil'));

  supplyPetrol.addEventListener('click', () => setMode('petrol'));
  demandPetrol.addEventListener('click', () => setMode('petrol'));
  supplyFuelOil.addEventListener('click', () => setMode('fueloil'));
  demandFuelOil.addEventListener('click', () => setMode('fueloil'));
</script>

</body>
</html>

Why do modern societies demand short-chain hydrocarbons so much more than long-chain ones?

An **alkane** is a saturated hydrocarbon containing only single covalent bonds between its carbon atoms, following the general formula $\text{C}_n\text{H}_{2n+2}$.

Short-chain alkanes like octane ($\text{C}_8\text{H}_{18}$) have weak intermolecular attractions, which means they are volatile liquids that vaporize easily and ignite cleanly as fuels.

Long-chain alkanes like eicosane ($\text{C}_{20}\text{H}_{42}$) have strong intermolecular forces, making them viscous and difficult to ignite, burning with a smoky flame.

<!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;
      color: #1e2945;
      background: transparent;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 12px;
      min-height: 100%;
    }

    /* Filter / Property Switcher */
    .controls {
      display: flex;
      justify-content: center;
      gap: 6px;
      flex-wrap: wrap;
    }
    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 12px;
      border-radius: 20px;
      cursor: pointer;
      transition: background 0.2s, color 0.2s, border-color 0.2s;
    }
    .btn.active {
      background: #22b7ff;
      border-color: #22b7ff;
      color: #ffffff;
    }

    /* Cards Grid */
    .grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      width: 100%;
    }
    @media (max-width: 480px) {
      .grid { grid-template-columns: 1fr; }
    }

    .alkane-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 14px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      box-shadow: 0 2px 6px rgba(30, 41, 69, 0.04);
    }

    .card-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      border-bottom: 1px solid #f1f5f9;
      padding-bottom: 8px;
    }
    .title-group {
      display: flex;
      flex-direction: column;
    }
    .name {
      font-size: 16px;
      font-weight: 700;
    }
    .formula {
      font-size: 13px;
      color: #64748b;
      font-weight: 500;
    }
    .badge {
      font-size: 11px;
      font-weight: 700;
      padding: 3px 8px;
      border-radius: 6px;
      letter-spacing: 0.3px;
      text-transform: uppercase;
    }
    .badge-short { background: #e0f2fe; color: #0369a1; }
    .badge-long { background: #fef3c7; color: #92400e; }

    /* Property rows */
    .prop-row {
      display: flex;
      align-items: center;
      background: #f8fafc;
      border: 1px solid #edf2f7;
      border-radius: 8px;
      padding: 8px 10px;
      gap: 10px;
      transition: background 0.2s, border-color 0.2s, opacity 0.2s;
    }
    .prop-row.dimmed {
      opacity: 0.35;
    }
    .prop-row.highlight {
      border-color: #22b7ff;
      background: #f0f9ff;
    }

    .prop-icon {
      font-size: 20px;
      width: 28px;
      text-align: center;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    .prop-info {
      flex: 1;
      display: flex;
      justify-content: space-between;
      align-items: center;
    }
    .prop-label {
      font-size: 13px;
      color: #64748b;
      font-weight: 500;
    }
    .prop-val {
      font-size: 13px;
      font-weight: 700;
    }

    /* Visual indicators */
    .meter {
      height: 6px;
      border-radius: 3px;
      background: #e2e8f0;
      overflow: hidden;
      margin-top: 3px;
      width: 100%;
    }
    .meter-fill {
      height: 100%;
      border-radius: 3px;
    }
    .fill-blue { background: #0284c7; }
    .fill-amber { background: #d97706; }
    .fill-red { background: #ef4444; }
  </style>
</head>
<body>

  <div class="controls">
    <button class="btn active" data-filter="all">Overview</button>
    <button class="btn" data-filter="viscosity">Viscosity</button>
    <button class="btn" data-filter="flame">Flammability</button>
    <button class="btn" data-filter="boil">Boiling Point</button>
  </div>

  <div class="grid">
    
    <div class="alkane-card">
      <div class="card-header">
        <div class="title-group">
          <span class="name">Octane</span>
          <span class="formula">C<sub>8</sub>H<sub>18</sub></span>
        </div>
        <span class="badge badge-short">Short Chain</span>
      </div>

      <div class="prop-row" data-type="viscosity">
        <div class="prop-icon">💧</div>
        <div class="prop-info">
          <div>
            <div class="prop-label">Viscosity</div>
            <div class="meter"><div class="meter-fill fill-blue" style="width: 20%;"></div></div>
          </div>
          <div class="prop-val">Low (Runny)</div>
        </div>
      </div>

      <div class="prop-row" data-type="flame">
        <div class="prop-icon">🔥</div>
        <div class="prop-info">
          <div>
            <div class="prop-label">Flammability</div>
            <div class="meter"><div class="meter-fill fill-amber" style="width: 90%;"></div></div>
          </div>
          <div class="prop-val">High (Clean)</div>
        </div>
      </div>

      <div class="prop-row" data-type="boil">
        <div class="prop-icon">🌡️</div>
        <div class="prop-info">
          <div>
            <div class="prop-label">Boiling Point</div>
            <div class="meter"><div class="meter-fill fill-blue" style="width: 30%;"></div></div>
          </div>
          <div class="prop-val">125 °C</div>
        </div>
      </div>
    </div>

    
    <div class="alkane-card">
      <div class="card-header">
        <div class="title-group">
          <span class="name">Eicosane</span>
          <span class="formula">C<sub>20</sub>H<sub>42</sub></span>
        </div>
        <span class="badge badge-long">Long Chain</span>
      </div>

      <div class="prop-row" data-type="viscosity">
        <div class="prop-icon">🍯</div>
        <div class="prop-info">
          <div>
            <div class="prop-label">Viscosity</div>
            <div class="meter"><div class="meter-fill fill-amber" style="width: 85%;"></div></div>
          </div>
          <div class="prop-val">High (Thick)</div>
        </div>
      </div>

      <div class="prop-row" data-type="flame">
        <div class="prop-icon">💨</div>
        <div class="prop-info">
          <div>
            <div class="prop-label">Flammability</div>
            <div class="meter"><div class="meter-fill fill-amber" style="width: 25%;"></div></div>
          </div>
          <div class="prop-val">Low (Smoky)</div>
        </div>
      </div>

      <div class="prop-row" data-type="boil">
        <div class="prop-icon">🌡️</div>
        <div class="prop-info">
          <div>
            <div class="prop-label">Boiling Point</div>
            <div class="meter"><div class="meter-fill fill-red" style="width: 90%;"></div></div>
          </div>
          <div class="prop-val">343 °C</div>
        </div>
      </div>
    </div>
  </div>

  <script>
    const buttons = document.querySelectorAll('.btn');
    const rows = document.querySelectorAll('.prop-row');

    buttons.forEach(btn => {
      btn.addEventListener('click', () => {
        buttons.forEach(b => b.classList.remove('active'));
        btn.classList.add('active');

        const filter = btn.dataset.filter;
        rows.forEach(row => {
          if (filter === 'all') {
            row.classList.remove('dimmed', 'highlight');
          } else if (row.dataset.type === filter) {
            row.classList.remove('dimmed');
            row.classList.add('highlight');
          } else {
            row.classList.add('dimmed');
            row.classList.remove('highlight');
          }
        });
      });
    });
  </script>
</body>
</html>

How can chemical engineers transform these sluggish, low-value long chains into the fuels and materials we actually need?

**Cracking** is a thermal decomposition reaction that breaks covalent bonds in long alkane molecules to produce shorter alkanes and **alkenes** (hydrocarbons with a double bond).

In 1891, Russian engineer Vladimir Shukhov patented the first industrial cracking unit to meet the world's exploding demand for lamp oil and engine fuel.

The alkene products act as **chemical feedstocks**—starting raw materials used in chemical manufacturing to produce essential plastics, solvents, and medicines.

<!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>Thermal Cracking of Decane</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
      user-select: none;
    }

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

    .diagram-root {
      width: 100%;
      max-width: 640px;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    /* Step header / status */
    .status-bar {
      display: flex;
      justify-content: space-between;
      align-items: center;
      font-size: 14px;
      font-weight: 600;
      color: #4b5563;
      padding: 0 4px;
    }

    .status-pill {
      background: #e0f2fe;
      color: #0369a1;
      padding: 4px 10px;
      border-radius: 12px;
      font-size: 13px;
      font-weight: 700;
    }

    /* Graphic Area */
    .canvas-container {
      width: 100%;
      height: 280px;
      position: relative;
      background: #f8fafc;
      border-radius: 12px;
      border: 1px solid #e2e8f0;
      overflow: hidden;
    }

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

    /* Heat Zone */
    .heat-zone {
      transition: opacity 0.5s ease;
      opacity: 0;
    }
    .heat-zone.active {
      opacity: 1;
    }

    /* Bond snip scissor/line */
    .snip-marker {
      stroke: #ef4444;
      stroke-dasharray: 4 3;
      stroke-width: 2.5;
      transition: opacity 0.4s ease;
    }

    /* Atom groups transitions */
    .octane-group, .ethene-group {
      transition: transform 0.8s cubic-bezier(0.4, 0, 0.2, 1);
    }

    /* Double bond highlight */
    .double-bond {
      transition: stroke 0.5s ease, opacity 0.5s ease;
    }

    /* Controls */
    .controls {
      display: flex;
      justify-content: center;
      align-items: center;
      gap: 8px;
      margin-top: 4px;
      flex-wrap: wrap;
    }

    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #334155;
      padding: 6px 14px;
      border-radius: 20px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      transition: background 0.2s, color 0.2s, border-color 0.2s;
    }

    .btn:hover {
      background: #e2e8f0;
    }

    .btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
    }

    .play-btn {
      width: 32px;
      height: 32px;
      padding: 0;
      justify-content: center;
      border-radius: 50%;
    }

    .legend {
      display: flex;
      justify-content: center;
      gap: 16px;
      font-size: 12px;
      color: #64748b;
      margin-top: 4px;
    }

    .legend-item {
      display: flex;
      align-items: center;
      gap: 5px;
    }

    .legend-dot {
      width: 10px;
      height: 10px;
      border-radius: 50%;
    }
  </style>
</head>
<body>

  <div class="diagram-root">
    <div class="status-bar">
      <span id="stage-title">1. Long Alkane Chain</span>
      <span class="status-pill" id="stage-badge">Decane (C₁₀H₂₂)</span>
    </div>

    <div class="canvas-container">
      <svg id="scene" viewBox="0 0 600 280">
        <defs>
          
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Why is it chemically impossible to crack an alkane into only smaller alkanes without forming an alkene?

## Balancing Saturated and Unsaturated Products

Starting from an alkane $\text{C}_n\text{H}_{2n+2}$, splitting the carbon chain leaves fewer hydrogen atoms than required for two full alkanes.

To ensure every carbon atom satisfies its **valency** of four covalent bonds, at least one resulting molecule must form a carbon-carbon double bond ($\text{C}=\text{C}$).

For example, cracking decane produces octane and ethene: $$\text{C}_{10}\text{H}_{22} \rightarrow \text{C}_8\text{H}_{18} + \text{C}_2\text{H}_4$$ Notice how the total counts of carbon ($10 = 8 + 2$) and hydrogen ($22 = 18 + 4$) remain strictly conserved.

If a chemical plant cracks dodecane ($\text{C}_{12}\text{H}_{26}$) to produce one molecule of hexane ($\text{C}_6\text{H}_{14}$) and two identical alkene molecules, what is the chemical formula of the alkene?

science

Why Cracking Is Necessary. Explain why large alkane molecules must be broken down into smaller, more flammable molecules and useful chemical feedstocks.

GCSE Chemistry: Cracking and Alkenes

Cracking Fractions of Crude Oil (KS4 Science / Chemistry)

Cracking & Alkenes GCSE Chemistry Revision Notes

To master this objective, instruction should start with the real-world economic context: contrast consumer fuel needs (high demand for short chains like petrol) against what comes out of fractional distillation (excess heavy fuel oil). Next, connect carbon chain length to physical properties (viscosity, boiling point, flammability) using kinetic particle theory and intermolecular forces. Emphasize that cracking is a chemical change (thermal decomposition) breaking covalent bonds, unlike fractional distillation which overcomes intermolecular forces. Finally, practice balancing cracking equations with atom conservation drills and link alkene products directly to the polymer and petrochemical feedstock industries.

Why Cracking Is Necessary

Chain Length and Physical Properties

Cracking and Feedstocks