We have to calculate the initial volume of a gas when a gas expands from a pressure of 1.60 atm to a pressure of 695 torr at constant temperature.

**We will solve this problem using the Boyle’s law.**

**Boyle’s law** states that the *volume of a gas varies inversely with the pressure applied on it.*

$\overline{){\mathbf{V}}{\mathbf{}}{\mathbf{\propto}}{\mathbf{}}\frac{\mathbf{1}}{\mathbf{P}}}$

**We can remove the proportionality sign to add “=” sign and a constant.**

$\mathbf{V}\mathbf{}\mathbf{=}\mathbf{}\mathbf{constant}\mathbf{\times}\frac{\mathbf{1}}{\mathbf{P}}\phantom{\rule{0ex}{0ex}}\overline{){\mathbf{PV}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{\mathbf{constant}}}$

**For two states of a gas:**

$\overline{){{\mathbf{P}}}_{{\mathbf{1}}}{{\mathbf{V}}}_{{\mathbf{1}}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{{\mathbf{P}}}_{{\mathbf{2}}}{{\mathbf{V}}}_{{\mathbf{2}}}}$

An ideal gas at a pressure of 1.60 atm is contained in a bulb of unknown volume. A stopcock is used to connect this bulb with a previously evacuated bulb that has a volume of 0.810 L as shown here. When the stopcock is opened the gas expands into the empty bulb.

If the temperature is held constant during this process and the final pressure is 695 torr , what is the volume of the bulb that was originally filled with gas?