# An ideal gas at constant temperature is conﬁned In an airtight cylinder, and a piston pushes down on the gas in the cylinder. Assuming the gas behaves as an ideal gas during the compression, what effect will this have on the pressure of the ideal gas?

You are compressing a gas. Is the volume going to increase? Is it going to decrease? If you compress the volume of a gas what is going to happen to pressure? Remember that pressure may be defined as amount of gas per unit volume. And for an ideal gas, $P$ $\propto$ $\frac{n}{V}$ at constant temperature.