The word ‘thermodynamics’ implies the flow of heat. It deals with energy changes accompanying all types of physical and chemical processes. It helps to lay down the criteria for predicting the feasibility or spontaneity of a process, including a chemical reaction, under a given set of conditions. It also helps to determine the extent to which a process, including a chemical reaction, can proceed before attainment of equilibrium. Thermodynamics is based on two generalizations called the first and second laws of thermodynamics. These are based on the human experience.

System: A system is defined as any specified portion of matter under study which is separated from the rest of the universe with a bounding surface. A system may consist of one or more substances.

Surroundings: The rest of the universe which might be in a position to exchange energy and matter with the system is called the surroundings.

Types of system

(i) Isolated system

A system which can exchange neither energy nor matter with its surrounding is called an isolated system.

(ii) Open system

A system which can exchange matter as well as energy with its surroundings is said to be an open system.

Macroscopic properties

The properties associated with a macroscopic system (i.e. consisting of large number of particles) are called macroscopic properties. These properties are pressure, volume, temperature, composition, density etc.