Chemistry 1A - Spring 2010 - Nitsche - Midterm 3 Solutions

# Chemistry 1A - Spring 2010 - Nitsche - Midterm 3 Solutions...

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Chemistry 1A, Spring 2010 Midterm 3 Solutions Apr 12, 2010 Problems 1. A 1.00 mol sample of CO 2 gas is confined in a 20.0 liter container at 25 C. If 1.00 mol of H 2 gas is added, holding the volume and temperature constant, the average kinetic energy of the system will ? A) Increase B) Decrease C) Remain the Same D) Not enough information to answer the question. Kinetic energy depends only on the temperature, so it will remain the same as temperature is held constant. 2. The average kinetic energy of the particles of a gas is directly proportional to ? A) the rms speed B) the square of the rms speed C) the square root of the rms speed D) the square of the particle mass 3 2 RT = E kin = 1 2 mv 2 rms 3. According to the kinetic-molecular theory, in which of the following gases with the root-mean-square speed of the molecules be the highest at 200 C? temperature), the lightest gas must have the highest velocity, as v rms r T M 4. According to the kinetic-molecular theory, if the temperature of a gas is raised from 100 C to 200 C, the average kinetic energy of the gas will ? 1

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Kinetic energy depends only on temperature. However, we must use the Kelvin scale, as it is an absolute scale, and we know that kinetic energy cannot be below zero. 100 C + 273 = 373 K 200 C + 273 = 473 K E kin,f E kin,i = 3 2 RT f 3 2 RT i = T f T i = 473 K 373 K = 1 . 27 Therefore, E kin,f is 1.27 times larger than E kin,i 5. Which of the following is NOT part of the kinetic-molecular theory? Kinetic-molecular theory has only to do with gases, not chemical reactions. 6. Which of the following statements is true for ideal gases, but it not always true for real gases? Mark all that apply. A) Collisions between molecules are elastic B) The size of molecules is unimportant compared to the distance between them. C) The volume occupied by the molecules is negligible compared to the volume of the container. D) Average molecular kinetic energy increases with temperature. A,B, and C are all true for ideal gases. However, for real gases, collisions are inelastic (due to intermolecular interactions), the size and volume of the molecules do matter (especially for phase transitions).
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