35   The Proportion of Heat Energy to Total Energy

What is the contribution of heat energy to the total energy of a volume of gas ? Does the mass of a gas cloud noticeably increase when it is heated ?

We calculate this contribution for 1 mol of helium at a temperature of 100 million K. In the rest system of the gas cloud, we determine the proportions as follows:

At a temperature of 100 million K, heat and thermodynamic work account for less than a thousandth of one percent of the rest energy due to mass ! And this rest energy precisely consists of the sum of the above three terms as stated in 23 . Heat and pressure likewise contribute to the inertia of the ensemble. Mass increases by jE / c2 jif thermal energy is added to the system. However, the rest energy due to heat and pressure is negligible.