AP | A-Level | IB | NCERT 11 + 12 – FREE NOTES, RESOURCES AND VIDEOS!
IB® (SL and AHL)
YouTube Channel
YouTube Channel
@chemistry.student
S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

R1.3 - Energy from fuels

1.3.1 Combustion Reaction 1.3.2 Incomplete Combustion 1.3.3 Fossil Fuels (CO2 Emission) 1.3.4 Biofuels and Renewable Energy 1.3.5 Fuel Cells and Half-Equations

Fossil Fuels, Carbon Dioxide, and the Greenhouse Effect

Specification Reference R1.3.3

Quick Notes

  • Fossil fuels include coal, crude oil, and natural gas.
    • When combusted, all release carbon dioxide (CO2).
    • The amount of CO2 released depends on:
      • The carbon content of the fuel.
      • The completeness of combustion.
      • The energy released per gram (energy density).
  • CO2 is a greenhouse gas, contributing to global warming.
  • Natural gas (mostly methane) burns more cleanly, releasing less CO2 per MJ of energy than coal.
  • Incomplete combustion can also produce carbon monoxide (CO) and soot (C).
  • The greenhouse effect traps thermal radiation in the Earth's atmosphere, warming the planet.

Full Notes

What Are Fossil Fuels?

Fossil fuels are non-renewable energy sources formed from ancient organic material. Main types include:

IB Chemistry diagram showing fossil fuels: coal, crude oil, and natural gas as major carbon-based energy sources.

Fossil fuels release energy through combustion reactions and because they contain carbon, also produce carbon dioxide (CO2).

Combustion and CO2 Production

The combustion reaction involves a hydrocarbon (or fossil fuel) reacting with oxygen.

Example Methane

CH4 + 2O2 → CO2 + 2H2O

Each carbon atom in the fuel produces one molecule of CO2 during complete combustion.

Comparing CO2 Emissions by Fuel

Fuel CO2 Emitted per MJ of Energy Notes
Coal Highest High carbon content, most CO2 per MJ
Crude oil Intermediate Mixture of hydrocarbons
Natural gas (CH4) Lowest Releases least CO2 per MJ

Natural gas releases the least CO2 per unit of energy and is often preferred for this reason.

Incomplete Combustion

Limited oxygen supply causes incomplete combustion (see here for more detail), which produces:

Larger hydrocarbons (with longer chains) require more oxygen to combust completely.

In most situations, especially with limited oxygen supply, it becomes more difficult to provide enough oxygen for full combustion, so they are more likely to undergo incomplete combustion.

Link to the Greenhouse Effect

Combustion of carbon containing fuels releases carbon dioxide (CO2) which is a greenhouse gas:

IB Chemistry diagram showing the greenhouse effect with CO2 trapping infrared radiation and causing global warming.

Evaluating Fuel Choices

When evaluating fuels, we must consider:

Cleaner alternatives (like methane) or renewable sources (like solar, wind, biofuels) are better options for reducing CO2 emissions.


AHL Structure 3.2 – Linked Course Question

Why is carbon dioxide described as a greenhouse gas?

Carbon dioxide is a greenhouse gas because it can absorb infrared (IR) radiation emitted by the Earth’s surface. Its molecular vibrations cause it to trap heat in the atmosphere, contributing to the greenhouse effect and global warming. This ability arises from its structure and polar bonds, which allow IR absorption.


Structure 3.2 – Linked Course Question

Why do larger hydrocarbons have a greater tendency to undergo incomplete combustion?

Larger hydrocarbons require more oxygen to combust completely, but in real conditions, oxygen supply is often limited, especially inside flames. Their size also makes them burn less efficiently, leading to incomplete combustion and the formation of carbon monoxide (CO) or soot (C) instead of carbon dioxide.


Nature of Science, Reactivity 3.2 – Linked Course Question

What are some of the environmental, economic, ethical and social implications of burning fossil fuels?

Burning fossil fuels releases greenhouse gases and pollutants, contributing to climate change, acid rain, and health issues. Economically, fossil fuels drive global industries but create long-term environmental costs. Ethically, their use raises questions about global responsibility and equity, as poorer communities often face the worst impacts. Socially, reliance on fossil fuels affects many areas including energy security and employment.

Summary