How Do Cars Run on Chemical Reactions?

by James Porter
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old engine image by John Sfondilias from

Cars provide us with a means of traveling long distances at great speeds with very little work. But you can’t get something for nothing. Through a series of chemical reactions, cars turn the liquid fuel into energy to get you from point A to point B.

Stored Energy

Gasoline consists mainly of medium-sized hydrocarbons, a fancy word for chains of carbon atoms linked together with hydrogen atoms around the outside. These molecules, with some oxygen thrown in, can reconfigure into carbon dioxide, carbon monoxide, and water along with some other by-products; but it takes heat to get them there. In other words, you have to burn it. In this configuration, they are more stable and have less internal chemical energy, so the transition from one to the other releases a lot of energy in the form of heat.

Chemical Reaction

A car engine uses this reaction to push its pistons. Inside the engine, the gas is sprayed into the combustion chamber above the piston. It is mixed with oxygen and then ignited. The reaction -- basically a little explosion -- heats it all up, making the air expand and push the piston outward. This is how the engine converts the gasoline’s chemical energy into mechanical force.

Mechanical Conversion

All of the pistons connect to a rotating crankshaft, timed so that when the reaction goes off and the hot air pushes the pistons down, they push with the crankshaft’s rotation. This way, the force from the expanding gas is used to put torque on the crankshaft. That rotation torque is transferred to the drive wheels so that it can move the car forward.

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