3- A piston cylinder system contains 1.0 Ibm of R134a at $P_1$ = 40 psi and
$T_1$ = 80 °F. It expands isothermally to $P_2$ = 10 psi. Find:
a) Change in the internal energy of R134a, $U_2$ - $U_1$. (2 points)
b) Change of the entropy of R134a, $S_2$ - $S_1$. (2 points)
c) The heat added to the R134a, $Q_{1-2}$. (3 points)
d) The boundary work, $W_{1-2}$. (3 points)
Note: °R = °F + 460