Question

Based on first law of thermodynamics which of the following is correct.

Options

• for an isobaric process, Q_P = ΔU + W

• for an adiabatic process, ΔU = - W

• for an isochoric process, ΔU = - Q_v

• for an isothermal process, Q = + W

Answer 1

for an isobaric process, Q_P = ΔU + W

Explanation:

In isobaric process, pressure is constant and volume increases from V, to V₂ due to the absorption of heat. According to the first law of thermodynamics, ΔU = Q + W

At constant pressure, Q_P = ΔU - W
Q_P = ΔU - pΔV

Q_P = U₂ - U₁ - (- p(V₂ - V₁))

Q_P = (U₂ + pV₂) - (U₁ + pV₁)

Q_P = H₂ - H₁

Q_P = ΔH

As we know, ΔH = ΔU + pΔV

ΔH - ΔU + W

Putting the value of ΔH in (1)

Q_P = ΔU + W

Other corrected options are as follows:

• for an adiabatic process, ΔU = - W
• for an isochoric process, ΔU = - Q_v
• for an isothermal process, Q = + W