Thermodynamics is a branch of physics which deals with the energy and work of a system. Thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments. Small scale gas interactions are described by the kinetic theory of gases. There are three principal laws of thermodynamics which are described on separate slides. Each law leads to the definition of thermodynamic properties which help us to understand and predict the operation of a physical system.
First Law of Thermodynamics
What is the first law of thermodynamics? (article) | Khan Academy
The three laws of thermodynamics define physical quantities temperature , energy , and entropy that characterize thermodynamic systems at thermal equilibrium. The laws describe how these quantities behave under various circumstances, and preclude the possibility of certain phenomena such as perpetual motion. The three laws of thermodynamics are:     . In addition, there is conventionally added a "zeroth law", which defines thermal equilibrium :. There have been suggestions of additional laws, but none of them achieve the generality of the four accepted laws, and they are not mentioned in standard textbooks. The laws of thermodynamics are important fundamental laws in physics and they are applicable in other natural sciences.
First law of thermodynamics
The first law of thermodynamics is the application of the conservation of energy principle to heat and thermodynamic processes:. The first law makes use of the key concepts of internal energy , heat , and system work. It is used extensively in the discussion of heat engines. The standard unit for all these quantities would be the joule, although they are sometimes expressed in calories or BTUs. It is the same law, of course - the thermodynamic expression of the conservation of energy principle.
In order to avoid confusion, scientists discuss thermodynamic values in reference to a system and its surroundings. Everything that is not a part of the system constitutes its surroundings. The system and surroundings are separated by a boundary.