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nR = PV/T (9.47)

Posted: Mon Feb 12, 2018 9:40 am
by Hannah Chew 2A
Hi! I'm not sure where I went wrong, but in 9.47, I tried substituting PV/T into nR in the equation delta S = nR ln (V2/V1). However, the answer I got was .0379 J/K instead of 3.84 J/K. Did I do something wrong, or am I mistaken in substituting PV/T into nR?

My work:
delta S = nR ln (V2/V1) = PV/T x ln (V2/V1) = 4.95atm x 1.67L / 323K x ln (7.33L/1.67L) = .0329 J/K

Correct Work:
n = PV/RT = 4.95 atm (1.67L) / 323K (.08206 Latm/molK) = .0312 mol
delta S = nR ln (V2/V1) = .0312 mol (8.314 J/molK) ln (7.33L/1.67L) = 3.84J/K

Any help is appreciated!

Re: nR = PV/T (9.47)  [ENDORSED]

Posted: Mon Feb 12, 2018 12:36 pm
by Deap Bhandal L1 S1J
Actually you did most of the calculation right. One thing though. When you did it, your units should be L*atm*K^(-1). One liter times atm equals 101.33 J so when you multiply your answer: 0.0379 by 101.33 you get around 3.84 just like the solution. Hope this helps!