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Problem Set 3

Page history last edited by Paul Cooper 10 years, 4 months ago

1)Calculate the molar entropy of a constant volume sample of nitrogen, N2, at 350 K given that it is 191.61 J K-1 mol-1 at 298 K.


2)Calculate ΔS (for the system) when the state of 2.50 moles of nitrogen, assumed to be an ideal gas, is changed from 25 °C and 2.00 atm to 125 °C and 8.00 atm.


3) Consider a system consisting of 3.0 moles of CO2(g), initially at 35 °C and 9.0 atm and confined to a cylinder of cross-section 100.0 cm2. The sample is allowed to expand adiabatically against an external pressure of 2.5 atm until the piston has moved outwards through 25 cm. Assume that carbon may be considered an ideal gas with a CV,m = 28.8 J K-1 mol-1, and calculate (a) q, (b) w, (c) ΔU, (d), ΔT, (e) ΔS.


4) The enthalpy of vaporization of ethanol is 43.5 kJ mol-1 at its normal boiling point of 352 K. Calculate (a) the entropy of vaporization of ethanol at this temperature and (b) the entropy of the surroundings.


5) Calculate the maximum non-expansion work per mole that be obtained from a fuel cell in which the chemical reaction is the combustion of ethanol at 298 K.


6) Calculate the Carnot efficiency of a primitive steam engine operating on steam at 180 °C and discharging at 100 °C. (b) Repeat the calculation for a modern steam turbine with steam at 360 °C and 100 °C.


7) Suppose that 2.5 moles of Ar(g) occupies 72 dm3 at 298 K and expands to 100 dm3. Calculate ΔG for the process.




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