Energy is the capacity of doing work and it has different forms. Energy can neither be created nor be destroyed but can be transferred from one form to another.
Thermodynamics is a branch of science that deals with the inter-conversion of one form of energy into another. In another word, it is the relation between energy change and chemical reaction.
Different terms used in thermodynamics:
The part of universe which is our observation is called system.
The part of our universe beyond the system is called surrounding.
The part of universe that separates system from surrounding is called boundary.
Types of system
The system which can exchange both matter and energy to the surrounding is called open system.eg water kept in open vessel.
The system which can exchange energy but not matter to the surrounding is called closed system.eg water kept in closed vessel.
The system which can neither exchange energy nor matter to the surrounding is called isolated system.eg water kept in thermos.