It is a science of energy transfer and its effect on properties of system
A system is a region containing energy and/or matter that is separated from its surroundings by arbitrarily imposed walls or boundaries. In a thermodynamic analysis, the systemis the subject of the investigation.
Everything external to the system is the surroundings.
A boundary is a closed surface surrounding a system through which energy and mass may enter or leave the system.
Isolated system (Special case of closed system)
An extensive property is a property that depends on the amount of matter in a sample. The mass of an object is a measure of the amount of matter that an object contains.
An intensive property is a property of matter that depends only on the type of matter in a sample and not on the amount.
E.g. Heat transfer to finite temperature difference, Free expansion.
(i) Mechanical equilibrium
Net force on a system should be 0, i.e. all the forces should be balanced.
(ii) Chemical equilibrium
All the chemical reactions occuring inside a system should cease after reaching equilibrium state.
(iii) Thermal equilibrium
There should be no heat transfer between the system and surroundings.