In Equation 14-20 the quantity \(c\) is the specific heat of the substance. For an ideal gas we usually write the internal energy \(U\) in terms of the number of moles of gas present rather than the amount of mass. We follow the same approach for the quantity of heat \(Q\), so we write
The quantity \(C\) in Equation 15-10 is called the molar specific heat of the substance (in the case we're discussing, an ideal gas). It has units of joules per mole per kelvin or \(\mathrm{J}\ /\ (\mathrm{mol}\cdot\mathrm{K})\).