Chemistry

What is Gasoline and what will Happen when it Runs out



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Gasoline - we call it petrol in the UK - makes the world go round. It is difficult to imagine what would happen to our daily lives if it ran out tomorrow. What is this liquid that our current society in the West depends on - and why is it such an excellent fuel that we have yet to find a viable alternative?

Gasoline is a fraction of crude oil - that is, it is a fossil fuel that was actually formed millions of years ago as sedimentary rock built up and exerted huge pressure on deposits of undecayed animal and plant matter, such as might form at the bottom of a lake, for example. Living things are made up of molecules that contain mainly carbon, hydrogen, oxygen and some nitrogen and sulphur. The huge pressures exerted by millions of tons of rock changed these compounds. The oxygen and nitrogen were removed, and compounds containing only carbon and hydrogen - hydrocarbons - were formed (tiny amounts of sulphur were left mixed in as an impurity). It is these hydrocarbons that constitute gasoline.

The hydrocarbons are what are called an homologous series of compounds. In fact, they are alkanes. That is why they have the general formula CnH2n+2. So pentane, for example, has the formula C5H12. So gasoline is a mixture of these alkanes that usually contains those from butane C4H20 to decane C10H22.

These alkanes are suitable for gasoline because while they are liquids at normal temperatures (making them a compact energy store), they have relatively low boiling points, which means that in the engine they will easily turn into gases and effectively mix with the air so that the explosive reaction with oxygen that drives an automobile can take place.

This reaction between alkanes and oxygen is one of the highest energy-yielding reactions in chemistry. An astonishing amount of energy is given out as carbon dioxide and water, two remarkably energy stable products, are formed. Unfortunately, some of the sulphur impurities will also oxidise and sulphur dioxide, an acid gas that can cause acid rain, is released. Low sulphur gasoline is currently available that will reduce this pollutant. Of course, the carbon dioxide is also a pollutant, and the hundreds of millions of automobiles on the road around the world are all releasing a massive amount into the atmosphere that may be contributing to global warming and the greenhouse effect.

The emissions of carbon dioxide and sulphur dioxide are one problem with gasoline as a fuel. Another, is that as a fossil fuel it is destined to eventually run out! No one really knows when but estimates are between 20 and 50 years supply now remains. Fuel shortages and increasing demand have already pushed gasoline prices up to unprecedented levels - again no one knows quite where it is leading us from here. This is a scary prospect and the conclusion can only be that Western governments fund research into alternative renewable fuels such as ethanol - that also have the benefit of being carbon neutral (that is returning to the atmosphere only the carbon that has recently been absorbed by the plant from which the ethanol was produced).

It is going to be an interesting spectacle to see what the scientists can come up with - our way of life, and possibly the future of our planet - may well be at stake.


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