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

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

For a finite change, ΔU = CvdT 

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

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