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Unformatted text preview: Version PREVIEW Exam 3 JOHNSON (53755) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. LDE Thermodynamic Theory 003 001 6.0 points Which of the following statements concerning the first law of thermodynamics is/are true? I) The internal energy of the universe is always increasing. II) Internal energy lost by a system is always gained by the surroundings. III) The universe is an isolated system. 1. I and III only 2. I only 3. II only 4. I and II only 5. I, II and III 6. II and III only correct 7. III only Explanation: Statement I is false; the first law states that the energy of the universe is conserved, in other words a constant value. Statement II and III are true; internal energy in the uni- verse is conserved, and thus energy lost by the system is always gained by the surroundings. The universe is the most obvious example of an isolated system in that energy and matter are conserved in the universe. LDE Definitions in Thermo 001 002 6.0 points Which of the following is not a definition of enthalpy or change in enthalpy? 1. A measure of a systems ability to change the entropy of its surroundings. 2. A correction for internal energy that ac- counts for pressure-volume work. 3. A measure of the motional energy of a system. correct 4. A measure of the heat of a system at constant pressure. Explanation: Total motional energy is a a measure of the internal energy ( U , or sometimes E ) of a system, not the enthalpy ( H ). LDE Sign Conventions 002 003 6.0 points You observe that carbon dioxide sublimes. Which of the following statements about the signs of this process is/are true? I) Work (w) is positive. II) Heat (q) is negative. III) Change in Gibbs free energy ( G ) is pos- itive. IV) Change in entropy ( S ) is positive. 1. III and IV 2. I and II 3. II and III 4. I only 5. I, II and III 6. IV only correct Explanation: Sublimation results in a significant increase in the volume of the system, allowing it to do work on its surroundings, i.e. the pressure-volume work function is negative. Sublimation is also an endothermic process, making heat positive. Since the process de- scribed happens as a given in the problem, the change in free energy must be negative. Change in entropy must be positive since a solid is becoming a gas. LDE Definitions in Thermo 002 004 6.0 points Which of the following quantities is not path Version PREVIEW Exam 3 JOHNSON (53755) 2 independent? 1. pressure (P) 2. entropy (S) 3. enthalpy (H) 4. heat (q) correct 5. volume (V) Explanation: Heat quantitatively describes a transition between states, but not a state itself, and is thus a process quantity (path function), not a state function....
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This note was uploaded on 03/04/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.
- Spring '07