The system consists of two moles of molecular oxygen, O 2 (g), contained in a di

ID: 780116 • Letter: T

Question

The system consists of two moles of molecular oxygen, O2(g), contained in

a diathermic cylinder sealed from the surroundings by a piston. In the initial state the

gas and cylinder are at a temperature of 278 K and pressure of 1.00 atm. The process

consists of heating the gas cylinder to 328 K under conditions where neither the

pressure, nor the volume is constant (Imagine for instance that the piston gets stuck

sometimes during the heating). In the final state the gas pressure is 1.08 atm.

Calculate DU and DH. If you have sufficient information to calculate q and w, do so. The

molar heat capacity at constant pressure for O2(g) is CP,m O = 29.38 J/K.mol. Assume ideal

gas behavior.

Cp = 29.38

Cp - Cv = R = 8.3

Cv = 21.08

dT =328 - 278 = 50

DU = n Cv dT = 2*21.08*50 = 2108 J

DH = DU + D(PV)

by ideal gas equation PV = nRT

DH = DU + D(nRT)

= DU + nR dT

= nCv dT + nR dt

= n(Cv + R) dT

= n( Cp) dT

= 2*29.38*50 = 2938 J

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