Question

Show that in the isothermal expansion of an ideal gas, ΔU = 0 and ΔH = 0.

Answer 1

For 1 mole of an gas, C_v = dU/dT or dU = C_v dT 

For a finite change, ΔU = C_vdT 

As ΔT = 0, Hence ΔU = 0. 

ΔH = ΔU + Δ(PV) = ΔU + Δ(RT) = ΔU + RΔT 

But as ΔU = 0 and ΔT = 0 (for isothermal process), 

Hence, ΔH=0