First law of thermodynamics

Equation (5) is the most general form of the first law of thermodynamics, e.g. the conversation of energy. The energy E in (5) includes all thinkable forms of energy, i.e. potential, kinetic, electric, magnetic energy of the container as a whole as well as the energy of the particles within the container itself, i.e. kinetic, rotational, vibrational energy of atoms and molecules, vibrational energy in solids as well as binding energies in any matter.

Now in the following we are not interested in E of the container itself. We want to know what is chemically going in the container and not what the container is doing itself. The latter is difficult to define anyway. The container could be sitting in a laboratory, in a train, or in a airplane which all travel with different speeds. Never the less the same chemical equilibria should apply as long the physical parameters as pressure and temperature within the container are identical. Moreover the earth on which the container sits has its speed and potential energy in respect to the sun. Again the sun has its speed and potential in respect to the milky-way’s center. Our galaxy travels in the universe, and the universe? Therefore the conditions outside of the container are not definable and irrelevant. Only the properties inside the container are of interest.

The energies inside the container are summarized as the inner energy U. Such the first law of thermodynamics becomes


But again there are some difficulties. Kinetic, rotational, vibrational energy of atoms and molecules, vibrational energy in solids as well as chemical binding energies are understandable. But what about binding energies within atomic nuclei? Protons, neutrons, and electrons consist of quarks, i.e. even smaller elementary building blocks. And even these quarks seem to consist of even small thinks like “strings”. As long we are interested in chemical bonding, i.e. the interaction of electrons within orbitals and of ions there is no need in further action. Reacting substances share the same protons, neutrons, and electrons and their individual binding energies in respect to smaller elementary particles will not change. Furthermore these energies have to be treated relativistically anyway. Therefore it is legitimate to truncate U at this point.