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Question
Although heat is a path function but heat absorbed by the system under certain specific conditions is independent of path. What are those conditions? Explain.
Solution
At constant volume
q = ΔU + (– w)
– w = pΔ q = AU + pΔV
ΔV = 0 .....(At constant volume)
Hence, qv = ΔU + 0 = ΔU = change in internal energy At constant pressure, qp = AU + pΔV
Since ΔU + pΔV = ΔH
⇒ qp = ΔH change in enthalpy
Hence, at constant volume and at constant pressure, heat change is a state function because it is equal to ΔU and ΔH respectively which are state functions.
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