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Question
Prove that ΔH=ΔU+ΔnRT. what is the condition under which ΔU=ΔH?
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Solution
∵ΔH=ΔU+PΔV
ΔH=ΔU+P(V2-V1)
ΔH=ΔU+PV2-PV1
But PV1 = n1RT
PV2 = n2RT
∴ΔH= ΔU+ n1RT - n2RT
ΔH= ΔU+RT(n1-n2)
| ∴ΔH= ΔU+ΔnRT |
Condition
i) When reaction is carried out in a closed vessel, so that volume remain constant ΔV=0
ii) When reaction involves only solids or liquids or solutions but no gaseous reactant or product.
iii) When reaction involves gaseous reactants and product but their number of mole are equal.
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