Question

$1000ml$ of a gas $A$ at $600torr$ and $500ml$ of gas $B$ at $800torr$ are placed in a $2L$ flask. The final pressure will be

• A. $2000$ torr
• B. $1000$ torr
• C. $500$ torr
• D. $1400$ torr

Answer 1

Answer: (C)

From Dalton’s partial pressure law
$P_1=\frac{1000}{1500}\times 600+\frac{500}{1500}\times 800$
$=400+\frac{800}{3}=\frac{2000}{3}$ torr
$V_1=1500mL$
$P_2=$ ? $V_2=2L=2000mL$
From $P\propto \frac{1}{V}$
$\frac{P_1}{P_2}=\frac{V_2}{V_1}$=
$\Rightarrow \frac{20003}{P_2}=\frac{2000}{1500}$
$\Rightarrow P_2=\frac{1500}{3}=500$ torr