# A container has a volume of 18 L and holds 9 mol of gas. If the container is compressed such that its new volume is 8 L, how many moles of gas must be released from the container to maintain a constant temperature and pressure?

The initial condition is $\frac{9 m o l}{18 L} = 0.5 \frac{m o l}{L}$.
The final condition is $0.5 \frac{m o l}{L} \times 8 L = 4 m o l$.