First law of thermodynamics
∆U = ∆Q -∆W
or ∆Q = ∆U + ∆W
In an ideal monatomic gas, the internal energy of the gas is simply translational kinetic energy of all its molecules.
the first law may be taken as a statement that there exists an internal energy function U that has a fixed value in a given state.
Remember that when work is done by the system,∆W is positive, If work is done on the system ∆W is negative.
When heat is given to the system ∆Q is positive. If heat is given by the system ∆Q is negative.
A positive ∆W decreases internal energy and a positive ∆Q increases internal energy.
Work done in an isothermal process on an ideal gas
W = nRTln(V2/V1)
Work done an isobaric process
W = p(V2-V1)
Work done an in isochoric process(volume of gas is constant)
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.