The first law ofthermodynamics, also known as the conservation of energy, provides a sound basis for studying the relationship among the various forms of energy, total energy, heat, and work. This states that energy can be neither created nor destroyed during any process. It can only change the forms.
When Q > O Heat transferred to system
When Q < O Heat transferred from system
When W > 0 Work done on system
When W < O Work done by system
The First Law ofThermodynamics can be denoted for a closed system by the formula given below-
Delta ( E ) = Q + W
Q = Heat energy
W = Work done
E = Total Energy
where Delta ( E ) is the total energy change in the system, Q the heat transferred, and W is the work done. Caution is given to the sign of work in Equations ; some books define work as positive when it is done by the system. The reason is that many engineering applications focus on the work that is only done by a particular heat engine alone, and so it is helpful to define that as positive.
In that case, Equation becomes that Total energy, is the extensive property and presents all the energy such as kinetic, potential, thermal, latent, chemical, nuclear, and others. All energy except kinetic and potential energy is called internal energy. The kinetic energy, is associated only with the motion of the body. The potential energy, is associated with the position of the body. In the case of a stationary system, Delta ( E ) = Delta ( U ). The potential energy may be present in a variety of fields (gravity, electric, or magnetic). The total energy is expressed as
E ( Total Energy ) = U ( Internal Energy ) + KE ( Kinetic Energy ) + PE ( Potential Energy )
Internal Energy can be defined as sum of Thermal Energy, Latent Energy, Chemical Energy, Nuclear Energy and other forms of energy.
Internal Energy ( U ) = Thermal Energy + Latent Energy + Chemical Energy + Nuclear Energy + Other forms of energy
The change of internal energy can be expressed thermodynamically as the following equation
The First law of thermodynamics can be given by the following equation
where Delta ( E ) is the rate of change of total energy in the system (being the same for both the system and the control volume for a closed system). In steady-state conditions (no change with time), the rate of change of energy in the system is zero (Delta ( É ) = 0 ).