It is shown in Section 3-8 that not all the energy supplied to a fluid stays in the fluid as increase in the internal energy of the fluid. In many cases, some part of or all the energy supplied to the fluid leaves the fluid as work. In Equation 4-1, The part of the transferred energy that is stored in the fluid as an increase in the internal energy is represented by the term u, whereas the part of the transferred energy that leaves the fluid as work is represented by the term pv/J is not stored in the fluid as an increase in the internal energy, it nevertheless represents energy that must be supplied to the fluid in order to bring the fluid to the given condition from the initial condition at the arbitrarily selected zero point of enthalpy. Also, this external work energy must pass back through and be given up by the fluid as the fluid returns to the initial condition.