Question

If a 1500 ml cylinder of a gas 'A' at 500 torr and a 500 ml cylinder of gas B at 1000 torr are connected by a thin tube, keeping the temperature same then what will be the final pressure (in torr)?

• A. 625
• B. 1250
• C. 750
• D. 875

Answer 1

The correct option is A 625

The total number of moles initially and finally must be the same.
Number of moles: $\frac{PV}{RT}$
Initial moles: $\frac{500\times 1500}{RT}+\frac{1000\times 500}{RT}$
When the tube is connected, the pressures in both the containers becomes the same. The total volume is the sum of the volumes of both the containers:1500 + 500 = 2000 $mL$
Final moles: $\frac{P\times 2000}{RT}$
Initial moles = final moles
$\frac{P\times 2000}{RT}$ = $\frac{500\times 1500}{RT}+\frac{1000\times 500}{RT}$
Final pressure $P=625torr$