So the heat capacity ratio is the ratio of the heat capacity at constant pressure to heat capacity at constant volume. Since there is no pressure in the vacuum, the heat capacity ratio of the vacuum should be zero. Is this right ?

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espava8b · Accepted Answer

The correct answer is       γ    =  N  a  N. That is to say there&#039;s not exactly one correct value. Imagine you take a gas and then expand its volume to an astronomical degree. What you&#039;ve created is effectively an ideal gas. The formula for the heat capacity ratio as a function of degrees of freedom f is      γ    =  1  +      2    f  and f isn&#039;t going to change as a function of density for an ideal gas. The only thing which actually matters is the case of how many degrees of freedom a single molecule has. So as density goes to 0,      γ   should remain constant. As you could&#039;ve used any gas(which could have any       γ  ) in the creation of this very low density vacuum,       γ   could be one of many values.

So the heat capacity ratio is the ratio of the heat capacity at constant pressure to heat capacity at constant volume. Since there is no pressure in the vacuum, the heat capacity ratio of the vacuum should be zero. Is this right?

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