What is classical thermodynamics?

The substance consists of a large no of particles called molecules. The properties of substances naturally depend on the behavior of these particles. For example, the pressure of a gas in a container is the result of momentum transfer between the molecules and the walls of the container. However, one does not need to know the behavior of the gas particles to determine the pressure in the container. It would be sufficient to attach a pressure gauge to the container. This macroscopic approach to the study of thermodynamics does not require knowledge of the behavior of individual particles. It is the overall behavior approach. It is called classical thermodynamics. It provides a direct and easy way to the solution of engineering problems.