Zeroth law: If two bodies A and B are in thermal equilibrium and A and C are also in thermal equilibrium then B and C are also in thermal equilibrium.
First law of thermodynamics
∆U = ∆Q -∆W
∆U = change in internal energy of a thermodynamic system
∆Q = Heat given to the system
∆W = work done by the system
Change in internal energy of a thermodynamic system is equal to the heat given to the system minus the work done by the system on surroundings or environment.
Second law of thermodynamics
It is not possible to design a heat engine which works in cyclic process and whose only result is to take heat from a body at a single temperature and convert it completely into mechanical work.
(Topic: Laws of Thermodynamics)