Water bath calorimetry was used to demonstrate one more peculiar phenomenon associated with a certain class of mixed gas plasmas, termed resonant transfer (RT) plasmas. Specifically, He/H2(10%) (500 mTorr), Ar/H2(10%) (500 mTorr), and H2O(g) (500 and 200 mTorr) plasmas generated with an Evenson microwave cavity consistently yielded on the order of 50% more heat than non-RT plasma (controls) such as He, Kr, Kr/H2(10%) under identical conditions of gas flow, pressure, and microwave operating conditions. The excess power density of RT plasmas was of the order 10 W cm-3. In earlier studies with these same RT plasmas it was demonstrated that other unusual features were present including dramatic broadening of the hydrogen Balmer series lines, unique vacuum ultraviolet lines, and, in the case of water plasmas, population inversion of the hydrogen excited states. Both the current results and the earlier results are completely consistent with the existence of a hitherto unknown exothermic chemical reaction, such as that predicted by Mills, occurring in RT Plasmas.