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Unformatted text preview: 812 Chapter 1 7 Free Energy and Thermodynamics Exercises Review Questions 1. 3. 7. 8. 9. 10. 11. 12. 13. What is the first law of thermodynamics and how does it relate to energy use? . What is nature’s “heat tax” and how does it relate to energy use? What is a perpetual motion machine? Is such a machine possible given the laws of thermodynamics? Is it more efficient to heat your home with a natural gas furnace or an electric furnace? Explain. . What is a spontaneous process? Give an example. . Explain the difference between the spontaneity of a reaction (which depends on thermodynamics) and the speed at which the reaction occurs (which depends on kinetics). Can a catalyst make a nonspontaneous reaction spontaneous? What is the precise definition of entropy? Explain the significance of entropy being a state function. Explain why the entropy of a gas increases when it expands into a vacuum. Explain the difference between macrostates (external arrange- ments of particles) and microstates (internal arrangements of particles). Based on its fundamental definition, explain why entropy is a measure of energy dispersion. Give the definition of the second law of thermodynamics. How does the second law explain why heat travels from a substance at higher temperature to one at lower temperature? What happens to the entropy of a sample of matter when it changes state from a solid to a liquid? From a liquid to a gas? Explain why Water spontaneously freezes to form ice below 0 °C even though the entropy of the water decreases during the phase transition. Why is the freezing of water not spontaneous above 0 °C ? 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. Why do exothermic processes tend to be spontaneous at low tem- peratures? Why does their tendency toward spontaneity decrease with increasing temperature? What is the significance of the change in Gibbs free energy (AG) for a reaction? Predict the spontaneity of a reaction (and the temperature depen- dence of the spontaneity) for each of the following (for the system): 3. AH negative, AS positive b. AH positive, AS negative c. AH negative, AS negative d. AH positive, AS positive State the third law of thermodynamics and describe its significance. Explain why the standard entropy of substance in the gas state is greater than its standard entropy in the liquid state. How does the standard entropy of a substance depend on its molar mass? On its molecular complexity? How is the standard entropy change for a reaction calculated from tables of standard entropies? What are three different ways to calculate AG“ for a reaction? Ex- plain which way you would choose to calculate AG° for a reaction at a temperature other than 25 °C. Why is free energy “free”? Explain the difference between AG° and AG. Explain why water spilled on the floor evaporates even though AG° for the evaporation process is positive at room temperature. How do you calculate the change in free energy for a reaction under nonstandard conditions? How is the value of AG° for a reaction related to the equilibrium constant for the reaction? What does a negative AG° for a reac- tion imply about K for the reaction? A positive AG°? Problems by Topic Entropy, the Second Law of Thermodynamics, and the Direction of Spontaneous Change 27. 28. 29. Which of the following processes are spontaneous? a. the combustion of natural gas b. the extraction of iron metal from iron ore c. a hot drink cooling to room temperature d. drawing heat energy from the ocean’s surface to power a ship Which of the following processes are nonspontaneous? Are the nonspontaneous processes impossible? a. a bike going up a hill b. a meteor falling to Earth c. obtaining hydrogen gas from liquid water d. a ball rolling down a hill Suppose a system of two particles, represented by circles, have the possibility of occupying energy states with 0, 10, or 20 I. Collec- tively, the particles must have 20 I of total energy. One way the two particles can distribute themselves is: 30. 31. 20] 10] oo 0] Are there any other energetically equivalent configurations? If so, which configuration has the greatest entropy? Suppose a system of three particles, represented by circles, have the possibility of occupying energy states with O, 10, or 20 I. Col- lectively, the particles must have 30 I of total energy. One way the two particles can distribute themselves is shown below. 20] 10] 01 Are there any other energetically equivalent configurations? If so, which configuration has the greatest entropy? 000 Without doing any calculations, determine the sign of ASS).s for each of the following chemical reactions: ...
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