# Question #df1ec

Mar 5, 2017

A coefficient tells you the relative amount (in moles or in molecules) of that chemical used or produced in the reaction.

#### Explanation:

Here is an example:

$C {H}_{4} + 2 {O}_{2} \rightarrow C {O}_{2} + 2 {H}_{2} O$

In this equation, the "2" in front of ${O}_{2}$ tells us that we will need twice as much oxygen gas as methane (the $C {H}_{4}$ molecule) to have this reaction work as the equation states. If we provide more, it will be left over, and not react. If we provide less, the reaction will not be able to use all the methane.

By the way, if there appears to be no coefficient, you assume that a "1" is there.

Then, on the right side of the arrow (the products) we see that one molecule of $C {O}_{2}$ forms at the same time that two molecules of water are produced.

This coefficients can have units that are either "molecules" or "moles" (if you are familiar with this unit). So we can read the equation as either

"One molecule of $C {H}_{4}$ plus two molecules of ${O}_{2}$ produce one molecule of $C {O}_{2}$ plus two molecules of ${H}_{2} O$"

or

"One mole of $C {H}_{4}$ plus two moles of ${O}_{2}$ produce one mole of $C {O}_{2}$ plus two moles of ${H}_{2} O$"