This is an example of the application of first law of thermodynamics to closed systems. -There is a bursting of a diaphragm separating high pressure gas compartment and vacuum compartment in a controlled volume. Consider the gas as the system. Assume that initial and final velocity are zero. I know that there is no work done and there is no heat transferred to the system. Therefore, there is no change in internal energy. What I don't understand is how we can use specific heat capacity at constant volume to explain that temperature (and hence internal energy) is unchanged for this ideal gas. My teacher wrote (capacity at constant volume)*(final temperature) = (capacity at constant volume)*(initial temperature) Would we say that this system is at constant volume?