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Chem 161-2011 some Chapter 10 practice problems Thermo (1)

# Chem 161-2011 some Chapter 10 practice problems Thermo (1)...

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Unformatted text preview: CHEM 161-2011 CHAPTER 10 THERMODYNAMICS PRACTICE PROBLEMS DR. ED TAVSS Heat and work (H&amp;amp;P Chapter 6 practice problems, 2010) Enthalpy (H&amp;amp;P Chapter 6 practice problems, 2010) Calorim. &amp;amp; Heat capacity (H&amp;amp;P Chapter 6 practice problems, 2010) Hesss Law (H&amp;amp;P Chapter 6 practice problems, 2010) Enthalpy of formn (H&amp;amp;P Chapter 6 practice problems, 2010) Bond energies &amp;amp; lengths (including lattice energies) (H&amp;amp;P Chapter 9 practice problems, 2010) 1 HEAT AND WORK 3 7 CHEM 161-2010 FINAL EXAM CHAPTER 6 - THERMOCHEMISTRY Heat and work A CD player and its battery together do 500 kJ of work, and the battery also releases 250 kJ of energy as heat and the CD player releases 50 kJ as heat due to friction from spinning. What is the change in internal energy of the system, with the system regarded as the battery and CD player together? A) +200 kJ B) - 700 kJ C) - 800 kJ D) - 200 kJ E) - 750 kJ Work = -500 kJ q = -(250 kJ + 50kJ) E = q + w E = -300 kJ -500 kJ = -800 kJ 3 CHEM 161-2010 FINAL EXAM CHAPTER 6 - THERMOCHEMISTRY Heat and work In the process of compressing a gas from 5.00 L to 2.50 L under a constant pressure of 1.25 atm, 637 J of heat is given off. What is the U of the system? 1 L-atm = 101.3 J. A. 320 J B. + 320 J C. + 954 J D. 954 J E. 634 J Gas Gas H = -637J 5.00L 2.50L 1.25atm 1.25atm H = q p U = q - PV U = -637J ((1.24atm x (2.50-5.00)) x (101.3J/Latm)) = -323 J 2 CHEM 161-2010 CHAPTER 6 - THERMOCHEMISTRY Heat and work 2. In which of the following processes is the sign of w negative when used to calculate U? X. A gas is compressed under 2.0 atm pressure Y. H 2 (g) + Cl 2 (g) 2HCl(g) Z. H 2 O( ) H 2 O(g) A. X only B. X and Y only C. Z only D. Y only E. X and Z only ET note: The problem could have been better worded if it said, In which of the following processes is the sign of w negative, for the system, when used to calculate U? w would be negative if the system does work on the surroundings, which means that the surroundings is compressed. X. False. If a gas is compressed, at any pressure, w for the system would be positive. Y. False. Going from two moles of gas to two moles of gas results in no change in volume; hence, the w is zero. Z. True. Going from a liquid to a gas expands the system, and compresses the surroundings. Hence, w for the system would be negative. Chem 161-2009 Final exam Hill, Petrucci et al. Chapter 6 Thermochemistry Heat and Work 12. What volume change will a system undergo if it emits 1.42 kJ of heat and U is -2.45 kJ and the external pressure is 1.23 atm? A. The system will be compressed by 8.27 L B. The system will expand by 8.27 L C. The system will be compressed 2.69 L D. The system will expand by 2.69 L E. The system will expand by 1.29 L 3 System ? V q = -1420J U = -2450J P = 1.23 atm U = q - PV (-2450J x (1Latm/101.3J)) = (-1420J x (1Latm/101.3J)) (1.23atm x V) Let X = V...
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Chem 161-2011 some Chapter 10 practice problems Thermo (1)...

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