I'm working on some code to simulate combustion at constant volume instead of constant pressure and I need to calculate the internal energy of formation for the species involved because I can only find the enthalpy of formation. I'm thinking of doing it this way:
- Simulate the formation reaction at constant pressure in whichever direction is exothermic and let it expand.
- Use the isentropic relations to compress the products back to the original volume isentropically.
- Find the internal energy of the products by integrating $C_V$ numerically from $298~\mathrm{K}$ to whatever temperature results from the isentropic compression.
Is this the right way to do this and/or is there a simpler way? I'm doing this all numerically so I can account for changing specific heats. Thanks.