### First Law of Thermodynamics

The first law of thermodynamics is the application of the conservation of energy principle to heat and thermodynamic processes:

The change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

Mathematically, ΔU (Change in Internal Energy) = Q (Heat added to or drawn from the system) – W (Work done by the system)

The First Law of Thermodynamics is equivalent to the Principle of Conservation of Energy.
Isothermal Process- An isothermal process is a thermodynamic process in which the temperature of the system remains constant. The heat transfer into or out of the system typically must happen at such a slow rate that the thermal equilibrium is maintained.

Adiabatic Process- An adiabatic process is a thermodynamic process in which there is no heat transfer (Q) into or out of the system. In other words Q = 0.

An adiabatic process is generally obtained by surrounding the entire system with a strongly insulating material or by carrying out the process so quickly that there is no time for a significant heat transfer to take place.

### Second Law of Thermodynamics

The Second Law of Thermodynamics states that in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state.

### Heat Engine

A heat engine typically uses energy provided in the form of heat to do work and then exhausts the heat which cannot be used to do work. Thermodynamics is the study of the relationships between heat and work. The first law and second law of thermodynamics constrain the operation of a heat engine. The first law is the application of conservation of energy to the system, and the second sets limits on the possible efficiency of the machine and determines the direction of energy flow.

Heat engines such as automobile engines operate in a cyclic manner, adding energy in the form of heat in one part of the cycle and using that energy to do useful work in another part of the cycle.

Heat Engine may be divided into two types-

Internal Combustion Engine- In this engine heat is produced in the engine itself. Example - Examples include gasoline engines, diesel engines, gas-turbine engines, and rocket-propulsion systems.

External Combustion Engine- In this engine heat is produced outside the engine. An example of external combustion engine is steam engine.

Refrigerator or Heat Pump- A refrigerator is an apparatus which transfers heat energy from cold to hot body at the expanse of energy supplied by an external agent. The working substance in the refrigerator is called refrigerant. In refrigerators, a refrigerant name Freon molecular formula CCl2F2 is used.