One-quarter lbmol of nitrogen gas $\left(\mathrm{N}_{2}\right)$ undergoes a process from $p_{1}=20 \mathrm{lbf} / \mathrm{in} .^{2}, T_{1}=500^{\circ} \mathrm{R}$ to $p_{2}=150 \mathrm{lbf} / \mathrm{in} .^{2}$, $T_{2}=800^{\circ} \mathrm{R} .$ For the process $W=-500 \mathrm{Btu}$. Employing the ideal gas model, determine
(a) the heat transfer, in Btu.
(b) the change in entropy, in $\mathrm{Btu} /{ }^{\circ} \mathrm{R}$.
(c) Show the initial and final states on a $T-s$ diagram.