# A container has a volume of 21 L and holds 15 mol of gas. If the container is compressed such that its new volume is 7 L, how many moles of gas must be released from the container to maintain a constant temperature and pressure?

$10 m o l$
Pressure($P$),Volume($V$),Number of $m o l$($n$),Gas constant($R = 0.082$), Kelvin temperature($T$)
$P V = n R T$
$P \cdot 21 = 15 R T \to P \cdot 7 = n R T \to n = 5$
So $15 - 5 = 10$ is the amount that needs to be released to maintain a constant temperature and pressure