Question

Three gases are mixed in a sealed container. The container has 0.3 moles of gas $A$, 0.4 moles of gas $B$, and 0.3 moles of gas $C$. The total pressure of the gases is 660 $torr$. What is true about the partial pressures of the gases?

• A. The partial pressure of gas $A$ is 264 $torr$
• B. The partial pressure of gas $B$ is 396 $torr$
• C. The partial pressure of gas $C$ is 220 $torr$
• D. The partial pressures of gases $A$ and $C$ are each 198 $torr$
• E. The partial pressure of gas $B$ is 660 $torr$

Answer 1

Answer: (D)

The partial pressures of gases $A$ and $C$ are each 198 $torr$

The partial pressures of gases $A$ and $C$ are each 198 $torr$
Since the number of moles of gas $A$ is equal to the number of moles of gas $C$, both gases have equal mole fraction and hence equal partial pressure.
The mole fraction is the ratio of number of moles of a gas to total number of moles of all gases. The mole fraction of gas $A$ $=\frac{0.3}{0.3+0.4+0.3}=0.3=$ the mole fraction of gas $C$.
The partial pressure of a gas is the product of its mole fraction and total pressure. The partial pressure of gas $A$ $=0.3\times 660=198$ $torr$ $=$ the partial pressure of gas $C$.