Answer Key - CHEM111 Week 6 Discussion Questions Fall 2014 1 Which of the changes will always increase the internal energy of a system Explain A The

Answer Key - CHEM111 Week 6 Discussion Questions Fall 2014...

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CHEM111 Week 6 Discussion Questions Fall 2014 1) Which of the changes will always increase the internal energy of a system? Explain. A. The system gains energy and performs work. (q = +, w = -; so magnitude of q and w are important, so not always) B. The system gains energy and work is performed on it. (ALWAYS Δ E = +) C. The system loses energy and performs work. (q = - , w = -, ALWAYS Δ E = -) D. The system loses energy and work is performed on it. (q= -, w = +; so magnitude of q and w are important, so not always) 2) In a steam engine, steam in a cylinder expands against a piston exerting 10 atm of external pressure. The volume of the cylinder increases by 10 L and simultaneously the steam cools, losing 3000 kJ of energy to the surroundings. What is the change in energy of the steam? (101.3 J = 1 L atm) P ext = 10. atm q = -3000 kJ Δ E = ? V inc = 10. L Δ E = q + w = -3000 kJ + [(-10. atm * 10. L)*(101.3 J / Latm)*( 1kJ/1000 J)] Δ E= -3010. kJ
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