FormatofSATIIPhysics(2)

　　1. A gas in a closed container is steadily heated over a period of time. Which of the following statements is true of this process?

　　(A)The average kinetic energy of the gas molecules decreases

　　(B)The mass of the container increases

　　(C)The pressure exerted by the gas on the walls of the container increases

　　(D)The gas changes phase into a liquid

　　(E)The specific heat of the gas decreases

　　Explanation　　The answer to this question is C. The key lies in remembering the ideal gas law: PV = nRT. According to this formula, an increase in temperature is accompanied by an increase in pressure. A is wrong, since the average kinetic energy of gas molecules corresponds to their temperature: if the temperature increases, so does the average kinetic energy of the molecules. B is wrong because we’re dealing with a closed container: the mass cannot either increase or decrease. D is wrong because a gas must be cooled, not heated, to change phase into a liquid. Finally, E is wrong because the specific heat of any substance is a constant, and not subject to change. We’ll touch on all this and more in Chapter 9: Thermal Physics.

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