Chemistry 141 Exam

1. In this question, you should think about the differences between real gases and ideal gases:

   1. Match the two curves in the plot below to 200K and 1000K for a gas.

1. At low temperatures, which of the following best describes the behavior of gases? CIRCLE ANSWER.

   1. At low temperatures, gases behave ideally and PV/nRT is approximately equal to 1.

   2. At low temperatures, the size of gas molecules becomes important and PV/nRT becomes less than 1.

• At low temperatures, gas molecules have a greater probability of attraction, and therefore causes less collisions with the container walls.

1. At low temperatures, the average kinetic energy is lower, so gases behave more ideally.

1. Circle the image below which most accurately would portray what you would expect to see at high pressures in a gas container. The red spheres are individual gas molecules in a container. Explain your choice!

            Explanation:

Chemistry 141 Exam

2. Consider a gas mixture of 2.5 moles of argon (Ar), 5.0 moles of neon (Ne), and 2.5 moles of helium (He). The three gases were in a 4.75 L container at 298K. What is the total pressure of the mixture and the partial pressure of neon (Ne) gas? Assume ideal gas behavior.

   1. A sample of helium (He) gas was expanded from 2.2 L initially at STP to 2.9 L. After expansion, the final temperature of the gas increased 25° What is the final pressure of the gas?

      2. Look at the graph below and think about Kinetic Molecular Theory to answer the following questions:

         1. In the graph above, label each curve above as O₂, N₂, H₂O, or He.

         2. Calculate the average kinetic energy of He gas at 298K in J/mol.

      Will the average kinetic energy of O₂ be smaller, larger, or the same as He at 298K?

DETAILED ASSIGNMENT

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