A 0.500 mol sample of the gas is held in a piston cylinder at 25 degree C. It ex
ID: 1065473 • Letter: A
Question
A 0.500 mol sample of the gas is held in a piston cylinder at 25 degree C. It expands against the atmosphere until the pressure inside the cylinder is equal to the atmospheric pressure of TOO torr. If the initial volume of the gas in the cylinder was 500.00 mL, how much work has been done by the He when the He pressure is equal to the atmospheric pressure? (R = 0.08206 L atm/mol K, 101 J/L atm) a. 11.9 kJ b. 030.4 kJ c. 046.5 d. 011.6 J An insulated thermos bottle is an example of a an open system. b. a closed system. c an isolated system. d. an undefined system.Explanation / Answer
Initial volume = 500ml =500/1000 L= 0.5 L, T= 25+273 =298K, n=0.5mol, Initial pressure ,P= nRT/V= 0.5*0.0821*298/0.5 = 24.46 atm
Final pressure, P2 =700 Torr =700/760 atm =0.92 atm
dV = RT*(1/P2- 1/P1)
Work done= -0.5*Pext*dV= -0.5*0.92*RT1*(1/P2- 1/P1)= -0.92*0.0821*298*(1/0.92-1/24.46)=-11.77 L.atm =11.77*101.3 =1192 J=KJ ( A is correct)
2. Thermos is an isolated system, since there is neither exchange of energy ( insulation) nor exchange of mass. ( C is correct)
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