Ten $\mathrm{kg}$ of steam at $500~\mathrm{bar}$ is expanded at constant pressure until its volume increases to seven times its initial value of $0.01~\mathrm{m^3}$.
(a) Calculate the initial and final temperature of the steam
(b) Calculate the heat that must be supplied to carry out the process
An attempt at solving this problem:
$$\Delta H + \Delta E_k + \Delta E_p = Q - W_S\ \ \text{(open system)}$$
Taking out unnecessary terms leaves us with
\begin{aligned}
\Delta H &= Q\\
500~\mathrm{bar} &= 5\cdot10^7~\mathrm{Pa}\\
\Delta H &= H_f - H_i\\
H_i &= (5\cdot10^7~\mathrm{Pa})\cdot(0.01~\mathrm{m^3}) = 5\cdot10^5~\mathrm{J}\\
H_f &= (5\cdot10^7~\mathrm{Pa})\cdot(0.07~\mathrm{m^3}) = 3.5\cdot10^6~\mathrm{J}\\
\end{aligned}
Converting to kJ/kg (10 kg of steam) \begin{aligned} \hat{H}_i &= 50~\mathrm{kJ/kg}\\ \hat{H}_f &= 350~\mathrm{kJ/kg}\\ \end{aligned}
And that's where I stopped. I tried looking up the values of $\hat{H}_i$ and $\hat{H}_f$ in steam tables to interpolate the temperatures, but the values are too low. Since the pressure is too high, I also know the ideal gas law $(PV=nRT)$ won't apply to this scenario. Can someone point me in the right direction?