Exam%201%202008

# Exam%201%202008 - 1 5 mol of a perfect gas is stored in a...

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1. 5 mol of a perfect gas is stored in a cylinder. Its C V,m is 2.5R. The cylinder is insulated except at the bottom, where it can exchange heat with a large piece of metal. Initially, the temperature and pressure of the gas are 25 o C and 3 bar, respectively. Then, the gas is allowed to expand isothermally against the external pressure maintained at 1 bar. When the piston stops, determine: (a) what is the work done by the gas? (b) how much heat is removed from the metal? (c) what are U, H, and S (1 bar = 10 5 kg/m/sec 2 , 1 J = 1 kg m 2 /sec 2 .) q Insulated wall Insulated piston Metal Solution. T 1 = T 2 = 25 0 C = 298 K p 1 = 3 bar, p 2 = 1 bar V 1 = nRT 1 /p 1 = 5*8.314*(298/3)*10 -5 m 3 = 4.129*10 -2 m 3 V 2 = nRT 2 /p 2 = 5*8.314*(298/1)*10 -5 m 3 = 12.388*10 -2 m 3 (a) w sys = p ex V = 10 5 *2*4.129*10 -2 J = 8.258 kJ (b) q = -w = w sys = 8.258 kJ (c) U = H = 0 1 3 2 p V (d) 2 3 3 1 T T p T T V rev

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Exam%201%202008 - 1 5 mol of a perfect gas is stored in a...

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