# A container has a volume of 4 L and holds 3 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?

Apr 11, 2018

If a container has a constant temperature and pressure this means it has a constant concentration.

#### Explanation:

In formulaic words:

${c}_{i} = {c}_{f}$

Hence, since:

$c = \frac{n}{v}$

${n}_{i} / {v}_{i} = {n}_{f} / {v}_{f}$

$\frac{3}{4} = {n}_{f} / 12$

${n}_{f} = 9$ $m o l$

Therefore, $6$ $m o l$ of gas must be added.