3.2 Practice problem answers

Keya Jani

  1. Solutions

    a) 2 mol gas

    b) 1 mol gas

  2. 5.5 mol of gas X, 1.0 mol of gas B and 3.5 mol of gas A

    a) 5.5 L of X, 1.0 L of B and 2.5 L of A

    b) 5.5 kPa of X, 1.0 kPa of gas B, 2.5 kPa of gas A

  3. Using Boyle’s Law, we can calculate the partial pressure of each gas in the new container, which has a combined volume of 5 L.

    PX1VX1=PX2VX2PX2=PX1VX1/VX2\ce{P1V1 = P2V2 → P2 = P1V1/V2}. For He\ce{He}, P2=(250)(3.5)/(5)=175 torrP_2 = (250)(3.5)/(5) = 175 \ce{\ torr}.

    For Ar\ce{Ar}, P2=(150)(1.5)/(5)=45 torrP_2 = (150)(1.5)/(5) = 45 \ce{\ torr}.

    By Dalton’s Law, the total pressure is the sum of the partial pressures, or 220 torr. By comparing the ratio of the pressure of Ar\ce{Ar} to the total pressure, we can obtain the mole fraction of Ar\ce{Ar}: 45/220=0.20545/220 = 0.205.