Components passing out of the System are given a negative value, since the System is losing that entity. The Internal Energy of the System is given the symbol, E . The Internal Energy is the sum of the kinetic and potential energies of all of the components of that system. Temperature is a measure of the average kinetic energy of the particles in a system.
Potential energy is energy of position .
In chemical terms, it is the energy arising from chemical bonds, holding atoms in positions relative to each other. This is mechanical work carried out by the expansion and contraction of Ideal gases. Later in the course we will look at Electrical work. There are many statements of the First Law. We have noted that the Universe is an isolated system, with no exchange of energy or mass.