Cv and work

[Ella Henrickson 3I]

From today's lecture, I am still confused on the relationship between Cv and Cp. I know that Cp has to be capable of doing work to change the volume to maintain pressure, but does Cv not do work, or there is just no work to be identified?

[Carina H - 2G]

Hi,

At a constant pressure, the volume can change. When a system does work to expand the system, the volume changes. So work can occur under constant pressure. However, when volume is constant, even as pressure increases or decreases, volume cannot change so work can't be done to make a change. Hope this is a helpful clarification!

[Aaron Li 1D]

In the system with the piston, if the volume is constant, the gas in the container does not push against the piston to move it and do work. The container at constant volume does not change, so no work is being done as the gas pushes against the container, so Cv does not include work.

[Samantha Melin 2E]

No, Cv does not do any work. In a scenario where the volume is forcibly held constant, resulting in a change in pressure instead. If it helps you remember, the equation for work is force multiplied by displacement. In this scenario, the piston would be held stationary, so its displacement would be zero (meaning there would be zero work done).

[Celine Khuu 2F]

At constant volume, no work can be done because the gas cannot do expansion work. Instead, the energy is released as heat.

[Madison Rhynhart 3H]

With a constant volume you run into the issue of the volume not being able to change due to the lack of ability to expand thus no work can be done and no energy will be expelled for that work. However under Cp, or constant pressure, there is the ability for expansion and thus volume change which causes work to occur, expelling energy and requiring the heat required for Cp to be higher than Cv to make up for the energy lost.