The discussion revolves around calculating the entropy change of an ideal gas during an expansion process. Participants explore the relevant equations, the role of heat capacity, and the implications of pressure in the calculations. The context includes theoretical and mathematical reasoning related to thermodynamics.
Participants express differing views on the role of pressure in the entropy calculation, with some unsure if it needs to be explicitly included. The discussion remains unresolved regarding the necessity of pressure in the calculations.
There are unresolved questions about the assumptions underlying the use of the entropy equation and the dependence on the ideal gas behavior, as well as the implications of the chosen path for calculating entropy change.
What equations do you know that relate to entropy? How does this relate to the heat capacity? Also, you've left most of your units off!ChristineMarie said:How do you calculate the entropy of an ideal gas with n = 1, Cv,m = 1.5R, Ti = 300K, P=3bar and expands against Pext = 1bar until final volume is twice initial volume at Tf = 200K?
To get the entropy change from the initial equilibrium state to the final equilibrium state of a system, you need to dream up a reversible path between these two states, and then evaluate the integral of dq/T for that path. In the case of an ideal gas, you also need to take into account the p-v-T relationship for the gas. The equation you wrote down takes all this into consideration, and has done all the work for you. So all you need to do is to substitute the volume ratio and temperature ratio in. The pressure is already implicitly taken into consideration by the equation.ChristineMarie said:I'm just not sure how to incorporate the pressures, if I even need to. But if I don't need to use the pressures I would like to understand why.