Question

Which one of the following equations does not correctly represent the first law of thermodynamics for the given processes involving an ideal gas? (Assume non-expansion work is zero)

Options

• Cyclic process: q = - W 

• Adiabatic process: ΔU = - W

• Isochoric process: ΔU = q

• Isothermal process: q = - W

Answer 1

Adiabatic process: ΔU = - W

Explanation:

1st law of thermodynamics we get,

ΔU = q + W

For cyclic process ΔU = O; q = - W (1^st option) is correct.

For adiabatic process q = 0

ΔU = W (2^nd option) is incorrect

For isochoric process;

ΔV = 0

Again W = P Δ V

∴ W = 0

∴ ΔU = q (3^rd option) is correct

For isothermal process, Δ = 0

∴ q = - W (4^th option) is correct