7. Combustion and fuels

What is combustion?

A chemical reaction where substances burn in oxygen, producing different products depending on the reactant.

What type of reaction is the combustion of metals?

A redox reaction where the metal is oxidized, oxygen is reduced, and an ionic compound is formed.

What is the general equation for metal combustion?

Metal + Oxygen → Metal Oxide.

What happens when sulfur combusts?

It forms sulfur dioxide (SO₂), which can further oxidize to sulfur trioxide (SO₃) and contribute to acid rain.

How does sulfuric acid form in the atmosphere?

SO₃ reacts with water: SO₃(g) + H₂O(l) → H₂SO₄(aq).

Why are alkanes relatively inert?

They have low bond polarity and strong C–C and C–H bonds.

What makes a fuel volatile?

Its ability to easily change from liquid to gas, which decreases as the carbon chain length increases.

What is LPG mainly composed of?

Compressed propane (C₃H₈).

What is the primary component of petrol (gasoline)?

Octane (C₈H₁₈).

What are the products of complete combustion of hydrocarbons?

Carbon dioxide (CO₂) and water (H₂O).

What is the general equation for the complete combustion of an alkane?

• Alkane + O₂ → CO₂ + H₂O.

Why is ethanol considered a biofuel?

It is produced from plants, making it renewable.

What is incomplete combustion?

A reaction where there is insufficient oxygen, producing carbon monoxide (CO) and/or carbon (soot).

Why is carbon monoxide dangerous?

• It binds irreversibly to haemoglobin, reducing oxygen transport in the blood.

What are fossil fuels?

Non-renewable energy sources like crude oil, coal, and natural gas.

Why is high activation energy useful for fuels?

It makes them kinetically stable, preventing spontaneous combustion.

What is the greenhouse effect?

The trapping of heat in Earth’s atmosphere by greenhouse gases like CO₂.

Why do longer hydrocarbon chains tend to undergo incomplete combustion?

They have stronger London dispersion forces, reducing volatility and affecting oxygen mixing.

What are biofuels?

Renewable fuels produced from organic matter via biological carbon fixation.

What is the process of ethanol production from glucose?

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.

Why do ethanol-based fuels have a lower carbon footprint than petroleum-based fuels?

The CO₂ released during combustion was previously absorbed by plants during photosynthesis.

Redox Reaction

A reaction where oxidation (loss of electrons) and reduction (gain of electrons) occur simultaneously.

Acid Rain

Rainwater that becomes acidic due to dissolved sulfuric acid from sulfur oxides in the atmosphere.

Complete Combustion

A reaction where a fuel burns in excess oxygen, producing CO₂ and H₂O.

Incomplete Combustion

A reaction where oxygen is limited, producing CO, soot, and less energy.

Volatility

The tendency of a substance to evaporate; higher volatility means lower boiling point.

Biological Carbon Fixation

The process where plants convert CO₂ into organic compounds through photosynthesis.

Ethanol Fermentation

The conversion of glucose into ethanol and CO₂ by microorganisms.

Carbon Footprint

The total amount of greenhouse gases emitted by an individual, process, or product.

Soot (Carbon Particles)

Solid carbon produced during incomplete combustion, contributing to pollution.