Absolute values typically are found at which the pressure of an ideal gas is zero.
For a given ideal gas the sound speed depends only on its temperature.
Air, under these conditions, is almost an ideal gas, but not quite.
The model of an ideal gas, however, does not describe or allow phase transitions.
Here we consider the simple case of mixing ideal gases.
Further results can be found in the classical section of the article on the ideal gas.
It is expected to lead to incorrect results for an ideal gas only under shock wave conditions.
The first term on the right-hand side is for an ideal gas.
For an ideal gas, the heat capacity is constant with temperature.
For dry air, which is approximately an ideal gas, we can proceed further.