Energy from gases

What is the connection between a tiny plant floating in the sea two hundred million years ago and someone cooking their breakfast on a gas oven? The tiny plant provided part of the gas that the oven is using.

There are billions of tiny plants and animals that float in the surface waters of the seas and oceans of the world. When they die, their bodies fall like rain to the ocean's floor and bacteria decompose them. These processes were also occurring in the ancient seas and oceans of the world. In some places a huge layer of dead bodies collected. They became buried by sand and rock before they decomposed. In time rock formed above them and squashed them. This caused the bodies to warm a little. The change in temperature brought changes to the bodies and gas and oil formed.

The gas and oil rose through gaps in the rocks until they reached rock that they could not pass through. There they stayed, with the gas like a huge bubble on the top of a lake of oil, until someone drilled down to the rock to reach them.

There are many gas and oil wells around the world. When gas is removed from a well it is cleaned then piped to towns. It may be stored in gasholders, which rise and fall as they fill and empty. When the gas is turned on in an oven it rushes out into the air and mixes with the oxygen. A spark is made by clicking a switch and the heat from the spark makes the gas and oxygen change. The gas burns in the oxygen and forms carbon dioxide and water. During this change large amounts of energy are released. Most of it is used to heat a pan and cook a meal but some is released as light, making a ring of flames on the hob.
While no one would have trouble thinking about how gas burns they may be surprised to find out that all substances that burn produce a gas first. When you light a candle, the heat from the match makes the wax in the wick turn to a vapour. The hot vapour mixes with oxygen in the air and burning begins. The wax vapour burns away to carbon dioxide and water vapour. If you push the end of a stick into a campfire you will find that in a few minutes it is burning like the rest of the wood. The wood is so hot that gases, called vapours, rise from it and mix with the air. The heat makes the vapours burn and carbon dioxide and water vapour are produced. Even a lump of coal, which looks like a black rock, produces gases, which mix with oxygen and burn when they are hot enough.

The energy from burning gases is used for a variety of purposes. In a power station it is used to boil water to make steam. This is used to make electrical generators work. In the home a candle may provide light when there is a power cut while burning gas may be used to provide heat for a central heating system. In the garden the gas from glowing charcoal provides heat to cook chops on a barbecue. Wherever we use heat it is generated by a hot gas mixing with oxygen.

Is natural gas always found with oil?
Not always. When gas is found with oil it is called wet gas. When it is found on its own it is called dry gas.

When gas is reached below ground does it just flow out steadily?
No. The gas in the rock may be at a pressure 250 times greater than air pressure. This means that when it is reached it will rush out strongly. If the gas has oil with it, the gas pressure is strong enough to make the oil shoot up and form a tall fountain.

Why does natural gas have to be cleaned?
It has to be cleaned because it contains carbon dioxide and sulphur dioxide. These two gases can make acids. If they got into the pipelines they could cause the metal to corrode and holes could develop. These would cause dangerous gas leaks.

Why is a gas leak dangerous?
It is dangerous because the gas mixes with the air. If someone then makes the mixture get hot the mixture will explode. Clicking a light switch can cause a spark that is strong enough to cause a gas explosion.

Why do things fall apart in an explosion?
When gas explodes it burns very, very quickly. This causes a great rise in temperature of the air. When air gets hot it expands. In an explosion the air expands so rapidly that it pushes very strongly on everything around it. This strong push can shatter windows and knock down walls.

What is the name of natural gas?
It is called methane. It is colourless and does not have a smell. Substances containing sulphur, called mercaptans, are added to the gas so it can be smelt if there is a leak.

What is coal?
Coal is a black rock but it is actually made from plants that lived about 350 million years ago. These plants formed vast forests in swamps. When they died they fell into the swampy water and did not decompose. In time a thick layer of dead plants built up which was covered by rock. The rock squashed and heated the dead plants and turned them into coal. In fact the gas which is collected from the North Sea has been made from coal and not from ancient sea life.

What is charcoal?
It is wood that has not been completely burnt. The wood is stacked and covered in turf and allowed to burn very slowly for many days. As there is a limited supply of oxygen the wood does not burn away but forms brittle black lumps. These can then be burnt in air. They are used in barbecues because they do not produce any smelly gases, which could spoil the taste of the food.

Why do spacecraft carry tanks of liquid oxygen?
The fuel used in rockets requires oxygen. There isn't any oxygen in space so it has to be taken on board the spacecraft. It is stored as a liquid to save room in the spacecraft. Hydrogen is used as a fuel in spacecraft and this is also stored in liquid form. A rocket engine has a compartment called a combustion chamber. When a rocket is to be fired in space, hydrogen and oxygen are mixed and heated in the combustion chamber. They produce a jet of hot gases which rush out at the back of the spacecraft and make it move through space.