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1.9.3Unit 1. Structure, Bonding and Introduction to Organic Chemistry

Combustion of Alkanes — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 6 parts Lesson 33 of 36 Unit quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
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Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
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Part 1 of 6Complete and Incomplete Combustion

Combustion reactions are strongly exothermic, which is why alkanes are useful as fuels.

Complete combustion
  • Complete combustion With plenty of oxygen, alkanes form carbon dioxide and water, as in C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.
General equation
  • General equation CₙH₂ₙ₊₂ + (3n + 1)/2 O₂ → n CO₂ + (n + 1) H₂O describes complete combustion for any alkane.
Incomplete combustion
  • Incomplete combustion With limited oxygen, carbon monoxide or carbon forms, for example 2CH₄ + 3O₂ → 2CO + 4H₂O.
Soot
  • Soot CH₄ + O₂ → C + 2H₂O shows carbon forming, which appears as a yellow, smoky flame.
Energy
  • Energy Complete combustion releases more energy per mole than incomplete combustion.

Part 2 of 6Pollutants and Their Effects

Pollutants and Their Effects
Carbon monoxide
  • Carbon monoxide A toxic gas that binds to haemoglobin in the blood and prevents it from carrying oxygen.
Sulfur dioxide
  • Sulfur dioxide Formed from sulfur impurities in fuel, it dissolves in rain water to form acid rain that damages buildings and ecosystems.
Nitrogen oxides
  • Nitrogen oxides High temperatures in engines make nitrogen and oxygen combine, N₂ + O₂ → 2NO, and these oxides contribute to smog and acid rain.
Unburnt hydrocarbons
  • Unburnt hydrocarbons These contribute to smog and some are harmful to health.
Carbon dioxide
  • Carbon dioxide Complete combustion produces this greenhouse gas, which increases global warming.

Part 3 of 6Reducing Pollution

1
Catalytic converters in car exhausts contain platinum and rhodium on a ceramic honeycomb.
2
They convert harmful gases to less harmful ones, for example 2CO + 2NO → 2CO₂ + N₂.
3
Flue gas desulfurisation passes power station gases through calcium oxide or calcium carbonate to remove sulfur dioxide.
4
The reaction CaO + SO₂ → CaSO₃ turns the gas into a solid that can be collected.
5
Lower sulfur fuels and improved engine design also cut emissions.

Part 4 of 6Calculations

Calculations
Mole ratios
  • Mole ratios The balanced equation gives the ratio of moles, so one mole of propane produces three moles of carbon dioxide.
Gas volumes
  • Gas volumes At the same temperature and pressure, gas volumes react in the same ratio as their moles, with water counted as liquid at room temperature.
Molar volume
  • Molar volume At room temperature and pressure, one mole of any gas occupies about 24 dm³.
Check
  • Check Always balance the equation first and confirm the state symbols before doing the mole calculation.

Part 5 of 6Worked Example

Question

  • Calculate the mass and volume at room temperature and pressure of carbon dioxide produced by complete combustion of 11.0 g of propane (Mr = 44.0;
    • molar gas volume 24.0 dm³ mol⁻¹).

  1. Balanced equationC₃H₈ + 5O₂ → 3CO₂ + 4H₂O.
  2. Moles of propane = 11.0 ÷ 44.0 = 0.250 mol, so moles of CO₂ = 3 × 0.250 = 0.750 mol.
  3. Mass of CO₂ = 0.750 × 44.0 = 33.0 g and volume = 0.750 × 24.0 = 18.0 dm³.

Answer 33.0 g of CO₂, which occupies 18.0 dm³.

Part 6 of 6Exam Checklist & Tips

1.9.3 – Key Points for the Exam

  • Complete combustion Burning in a plentiful supply of oxygen to give carbon dioxide and water only.
  • Incomplete combustion Burning in limited oxygen to give carbon monoxide or carbon as well as water.
  • Catalytic converter A device that removes pollutants from exhaust gases using a metal catalyst.
  • Acid rain Rain made acidic by dissolved sulfur dioxide and nitrogen oxides.
  • Flue gas desulfurisation Removal of sulfur dioxide from waste gases from power stations.

Common Mistakes

  • Balancing the equation by changing subscripts rather than coefficients.
  • Forgetting to count the oxygen atoms in both CO₂ and H₂O.
  • Saying carbon monoxide is poisonous because it is acidic.
  • Writing the product of incomplete combustion of every alkane as only carbon.

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