# A container has a volume of 3 L and holds 7 mol of gas. If the container is expanded such that its new volume is 15 L, how many moles of gas must be injected into the container to maintain a constant temperature and pressure?

Jul 17, 2018

28 mol

#### Explanation:

$P \times V = n \times R \times T$

P is pressure
V is volume
n is mol
R is the universal gas constant
T is temperature.

1st situation:
$P \times 3 = 7 \times R \times T$

2nd situation
$P \times 15 = n \times R \times T$

P is the same in the 1st and 2nd situations. R and T are the same also (n is the moles in the second situation).

$\frac{3}{15} = \frac{7}{n}$

$n = \frac{7 \times 15}{3} = 35$ moles (total in the second situation. It means there are $35 - 7 = 28$ moles of gas must be injected to have the condition.