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Question

Two moles of an ideal gas is heated at constant pressure of one atomsphere from 27C to 127C. if Cv,m=20+102T JK1mol1 then Heat (q) and Internal energy (U) for the process are respectively:

A
6362.8 J, 4700 J
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B
3037.2 J, 4700 J
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C
7062.8 J, 5400 J
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D
3181.4 J, 2350 J
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Solution

The correct option is A 6362.8 J, 4700 J
Calculating w using :
w=PV=nRT (for an ideal gas)
w=nRT=2×8.314×100=1662.8 J

now molar heat capacity at constant volume is given as
Cv=dUndT or

dU=nCvdT
given, Cv=20+102T
T1=300 K and T2=400 K so,
integrating both sides from T1 to T2 :

U=n400300(20+102T)dT=2[20×T+1022(T2)]=2[20×(T2T1)+1022(T22T21)]=2[20×100+1022(40023002)]So,U=4700 J

also U=q+w
4700=q1662.8q=6362.8 J

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