The first law of thermodynamics states that a change in internal energy is possible only with external influences. In other words, if a certain amount of heat is communicated to the system and work is done on it, then the activity of this body will increase.
The first law of thermodynamics, the definition of which is the law of conservation of energy, applies only to systems with macroscopic dimensions. It is a mathematical expression of the first principle of science studying the general properties of systems. This is thermodynamics.
The state of the system can be changed using two completely different methods. The first of them is associated with the action of moving surrounding bodies over distances that are defined as macroscopic. It is also possible to work in the immediate vicinity of objects on the system. The second method involves the transfer or removal of thermal energy. In this case, the bodies surrounding the system do not change their location.
The first law of thermodynamics states that the initial and final quantities of thermal energy and work are characteristics of the process that takes place on the substance in question. In the case when the system completes a closed cycle, returning to its original state, the magnitude of the temperature effect will be similar to the work that the body will do.
The first law of thermodynamics allows us to conclude that there is a concept of internal energy. It is a characteristic of the state of the system. There are likely cases when the internal energy of an isolated body remains unchanged. In this case, heat exchange occurs only between substances inside the system. Then the amount of heat that flows from the cooling bodies is equal to its quantity flowing to the heated bodies. The total internal energy of the closed system is unchanged. This condition is a heat balance.
If a certain amount of energy is transferred to the system, then the internal activity of the body is taken as a positive value, and in the reverse processes - as negative.
Chemistry also applies the first law of thermodynamics in its research. It is believed that internal energy is stored in a kinetic state. Its expression is the movement of ions, atoms and molecules. In addition, the energy of the system is stored in intranuclear forces and chemical bonds. The absolute value of the activity of a substance cannot be determined. In connection with this, its change associated with a specific process is established.
The first law of thermodynamics in chemistry considers work as an expansion of matter. Its action is directed as opposed to external atmospheric pressure. The positive value of such work means that the system increases its internal energy. With a negative value, loss occurs.
Work, as well as heat, is not a property of the system. These parameters are used to characterize the interaction of a substance with its environment. The work in this case serves as a quantitative expression of the transfer of molecular motion, which is ordered, and heat - the equivalent of chaotic movement. This is especially pronounced in chemical reactions. If the process has not entered its initial stage or has already completed, it is impossible to confirm the presence of work and heat in the system. During a chemical reaction, all atoms are rearranged. In this case, some bonds are destroyed, while others are formed. The result is a change in the internal state of the system and its energy. These transformations cause the outflow of heat from the substance into its environment.
According to the first principle of thermodynamics, the operation of any mechanism is provided due to a certain amount of heat that must be obtained from the outside, or by reducing its internal energy. Thus, the efforts of many inventors trying to construct a perpetual motion machine, were initially doomed to failure.