Thermodynamics | 1st law of thermodynamics

1^st law of thermodynamics

It states, energy can neither be created nor be destroyed. The total energy of universe remains constant.

E₂ = E₁ + q + w

E₂ – E₁ = q = w

∆E = q + w is mathematical statement of 1st law of thermodynamics

‘q’ is not a state function, w is not a state function but q + w = ∆E is a state function.

a). For isothermal process: ∆E = 0, q = – w, i.e., heat absorbed by system is equal to work by the system.

b). For isochoric process: ∆V = 0, w = p ∆V = 0, ∆E = q", i.e., change in internal energy is e to heat exchanged with the surroundings at constant volume.

c). For adiabatic process: q = 0, ∆E = w, i.e., internal energy change is equal to work done on the system.