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How has the Earth's atmosphere changed over time, and why?How human activities affect the atmosphere

The Earth, its oceans and atmosphere are made of elements and compounds in different states. The particle model may be used to explain the different properties of the solid, liquid and gas states.

Part of Combined ScienceAir and water

How human activities affect the atmosphere

A reaction in which oxygen combines with another substance is called an reaction.

react rapidly with oxygen, transferring to the surroundings by heating and by light. This type of oxidation reaction is known as burning or . The products of combustion then enter the .

Hydrocarbon fuels

are that contain hydrogen and carbon only.

Hydrocarbon fuels can undergo or , depending on the amount of oxygen available.

Complete combustion

Complete combustion of a hydrocarbon fuel happens when there is a good supply of air or oxygen. Carbon and hydrogen in the fuel react with oxygen:

  • carbon dioxide and water are produced
  • energy is given out

In general:

hydrocarbon + oxygen 鈫 carbon dioxide + water

Question

Write a balanced chemical equation for the complete combustion of propane (C3H8) with oxygen (O2). Explain why the equation is balanced.

Incomplete combustion

Incomplete combustion happens when the supply of air or oxygen is poor. Water is still produced, but carbon monoxide and carbon are the other products. Less energy is released than during complete combustion.

Here is one possible equation for the incomplete combustion of propane:

propane + oxygen 鈫 carbon monoxide + carbon + water

C3H8 + 3O2 鈫 2CO + C + 4H2O

Notice that fewer oxygen molecules are needed to balance the equation than are needed for the complete combustion of propane.

Soot

The carbon is released as fine black , which we can see in smoky flames, and is deposited as . Soot can cause breathing problems and it blackens buildings. It may block boilers and other appliances, or cause a fire.

Factory chimneys producing smoke
Image caption,
Incomplete combustion produces smoke and invisible carbon monoxide

Carbon monoxide

Carbon monoxide is a gas. It is absorbed in the lungs and binds with the in the . This reduces the capacity of the blood to carry oxygen. Carbon monoxide causes drowsiness, and affected people may fall unconscious or even die.