The first law of thermodynamics is briefly introduced, and its significance is expounded from the microscopic point of view.

Key words: first law of thermodynamics, internal energy, heat, work.

Text:

The first law of thermodynamics: also known as the principle of energy invariance, is the law of energy conservation.

The first law of thermodynamics points out that thermal energy can be transferred from one object to another, and can also be converted with mechanical energy or other energy. In the process of transfer and conversion, the total value of energy remains unchanged.

The energy represen a thermodynamic system is internal energy. By doing work and heat transfer, the system exchanges energy with the outside world, which changes the internal energy. According to the general law of conservation of energy, after the state of the system reaches the final state 2 through any process, the increment e of internal energy should be equal to the difference between the heat q transferred to the system by the outside world and the work w done by the system to the outside world in this process, that is, E2-E 1=E=Q-W or Q = E+W, which is the expression of the first law of thermodynamics. If besides doing work and heat transfer, there is energy Z brought by matter entering the system from the outside, it should be U = Q-A+Z. Of course, it is above.