Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Atomic/molecular collisions and pressure The kinetic-molecular theory relates pressure to elastic collisions between individual particles and the walls of the container. Even though atoms/molecules are light, they move at hundreds or even thousands of m/s, and each contributes significant kinetic energy.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Consider two specimens of ideal gas at the same temperature. The molecules in specimen #1 have greater molar mass than the molecules in specimen #2. How do the rms speed of molecules (v rms ) and the average translational kinetic energy per molecule (KE) compare in the two specimens? A. v rms and KE are both greater in specimen #2. B. v rms is greater in specimen #2; KE is the same in both specimens. C. v rms is greater in specimen #2; KE is greater in specimen #1. D. Both v rms and KE are the same in both specimens. E. None of the above is correct. Q18.3
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Consider two specimens of ideal gas at the same temperature. The molecules in specimen #1 have greater molar mass than the molecules in specimen #2. How do the rms speed of molecules (v rms ) and the average translational kinetic energy per molecule (KE) compare in the two specimens? A. v rms and KE are both greater in specimen #2. B. v rms is greater in specimen #2; KE is the same in both specimens. C. v rms is greater in specimen #2; KE is greater in specimen #1. D. Both v rms and KE are the same in both specimens. E. None of the above is correct. A18.3
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Consider two specimens of ideal gas at the same temperature. Specimen #1 has the same total mass as specimen #2, but the molecules in specimen #1 have greater molar mass than the molecules in specimen #2. In which specimen is the total translational kinetic energy of the entire gas greater? A. specimen #1 B. specimen #2 C. The answer depends on the particular mass of gas. D. The answer depends on the particular molar masses. E. Both C. and D. are correct. Q18.4
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Consider two specimens of ideal gas at the same temperature. Specimen #1 has the same total mass as specimen #2, but the molecules in specimen #1 have greater molar mass than the molecules in specimen #2. In which specimen is the total translational kinetic energy of the entire gas greater? A. specimen #1 B. specimen #2 C. The answer depends on the particular mass of gas. D. The answer depends on the particular molar masses. E. Both C. and D. are correct. A18.4
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Expanding Helium Helium gas starts at a volume V i = 1L and P i = 1 atm. It expands linearly to V f = 3L and P f = 3 atm. 1.Draw the pV diagram for this process 2.What is the work done by the gas when it expands? 3.What is its increase in thermal energy? 4.How much heat is gained or lost by the gas?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Speed of air molecules What is the average translational kinetic energy of one molecule an ideal gas of oxygen (molar mass M = 32 g/mol) at 27°C? What about nitrogen (molar mass M = 28 g/mol)? What is the rms speed of nitrogen and oxygen?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley How much heat energy can ensembles contain? An atom can absorb energy as the kinetic energy of its motion. A molecule can absorb energy in its translation, and also in its rotation and in the vibrations of one atom in its structure with respect to the others. Atomic/molecular energy absorbed is termed its “heat capacity.”
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Illustration of heat absorption into degrees of freedom
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Energy of monatomic and diatomic gases How much heat is required to raise 4g of He gas from 300 K to 310 K? How about hydrogen gas H 2 ? What is the rms speed of He gas and H 2 at 300K?