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What flows



In a recent note someone gave an example of an explosion in a cylinder
that would show that the term "thermal energy" would be useful. The
statement used an adiabatic wall, so dQ = 0, the walls were rigid, so
dV = 0 and no work was done, therefore from the first law of thermo-
dynamics it followed that dU = 0. Yet, the inside gas was at a
higher temperature, so that was due to thermal energy. Actually, the
expression for the first law of thermodynamics had been written in an
incomplete form. For an explosion to be possible the original gas
could not have been a simple substance, it must have been, for example,
a mixture of gasoline vapor and oxygen gas. It was Gibbs who made
the great contribution to chemistry by extending thermodynamics to
chemical reactions in 1878 with his paper: "On the equilibrium of
heterogenous substances." The added terms to the first law were in
the nature of udm for each substance; it is more customary now to use
dn instead of dm. In conclusion, it is not true that dU = 0 in the
example above. Thermal energy, which sounds like temperature energy,
has no place in physics, the energy of a body is its internal energy.