State first law of thermodynamics in different ways.

(i) Energy can neither be created nor destroyed, though it may be converted from one form into another.
(ii) The total energy of an isolated system remains constant, although there may be internal changes in the state of the system.
(iii) It is impossible to construct a perpetual motion machine i.e. a machine that can produce work without any expenditure of energy.
(iv) Total energy of a system and its surrounding such as universe remains constant in any physical or chemical process.