- #1
Urmi Roy
- 753
- 1
So from the first law for a closed system,
dU=dQ-dW=dQ-PdV
From the second law,
dS=dQ/T + Sgenerated (i.e. the entropy generated)
Putting expression of dQ from second law into first law,
dU=T*dS-T*Sgen-PdV
If s and v are constant,
dU= -T*Sgen>0
Hence dU<0
This is a derivation that was given in class
My questions are as follows:
1. When we say s is constant, does it mean there is not heat flow into/out of the system?
2.If dU<0, does the temperature decrease? I find it hard to understand how there can be a positive Sgen and decrease in temperature/ internal energy simultaneously!
dU=dQ-dW=dQ-PdV
From the second law,
dS=dQ/T + Sgenerated (i.e. the entropy generated)
Putting expression of dQ from second law into first law,
dU=T*dS-T*Sgen-PdV
If s and v are constant,
dU= -T*Sgen>0
Hence dU<0
This is a derivation that was given in class
My questions are as follows:
1. When we say s is constant, does it mean there is not heat flow into/out of the system?
2.If dU<0, does the temperature decrease? I find it hard to understand how there can be a positive Sgen and decrease in temperature/ internal energy simultaneously!