Fluids: Liquids and Gases

Assessment Problems

  • 1. Flask A has three times the volume but holds three times as many gas molecules as flask B at the same temperature.  Compare the pressure in the two containers.

    Answer: The pressure in each container would be the same. The ratio of volume to the number of moles of gas at constant temperature is a constant. So tripling both the volume and the number of molecules would result in the pressure being unchanged.

  • 2. What effect will a decrease in pressure and an increase in temperature have on the volume of a fixed amount of gas?

    Answer: At a lower pressure, the volume will increase. Increasing the temperature will also cause an increase in volume. Therefore, the net result is a larger volume.

  • 3. A sample of air occupies a volume V at a temperature T and pressure P.  If the temperature remains constant, what volume will the gas occupy if the pressure is reduced to P/4?

    Answer: Boyle’s Law states that at constant temperature, the product PV is a constant. Thus, if the pressure is reduced to ¼ its initial value, the volume will have to increase by a factor of 4 to maintain the constant. The new volume will therefore be 4V.

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