# A container has a volume of #4 L# and holds #2 mol# of gas. If the container is expanded such that its new volume is #12 L#, how many moles of gas must be injected into the container to maintain a constant temperature and pressure?

##### 1 Answer

#### Explanation:

We can solve this problem by using the quantity-volume relationship of gases, illustrated by *Avogadro's law*:

We need to find the new quantity of gas when the volume is increased from

This is the *total* number of moles that satisfies the equation; we're asked to find how many need to be *injected*. The number of moles that you need to add is simply the total final moles minus the initial moles:

Thus, you need to inject