- #1
JC2000
- 186
- 16
- Homework Statement
- In an adiabatic expansion, a gas does 25J of work while in an adiabatic compression, 100 J of work **is done on** the gas. Find the change in internal energy for the processes.
- Relevant Equations
- ## dQ = dU + dW ## (where dW is the work done by the gas) ... (1)
## dQ = 0## for adiabatic processes. ... (2)
## W = \frac {nR(T_1 - T_2)}{\gamma -1}## (not required but relates to my question)... (3)
Using (2) on (1) give ## dU = -dW##... (4)
A.For expansion since the gas goes from ##(P_1, V_1, T_1)## to ##(P_2, V_2, T_2)##, does this imply ##T_1 \leq T_2 ##?
B. If so, then ##W## for adiabatic expansion would be negative (using (3))? Using negative ##dW## in (4) gives us a positive result for ##dU##?
C. For compression, it would be the opposite?
D. But since the question mentions work done on the gas we can read this as negative work done by the gas, which gives us the same sign as in B.?
A.For expansion since the gas goes from ##(P_1, V_1, T_1)## to ##(P_2, V_2, T_2)##, does this imply ##T_1 \leq T_2 ##?
B. If so, then ##W## for adiabatic expansion would be negative (using (3))? Using negative ##dW## in (4) gives us a positive result for ##dU##?
C. For compression, it would be the opposite?
D. But since the question mentions work done on the gas we can read this as negative work done by the gas, which gives us the same sign as in B.?