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Questions
Write the mathematical equation of the first law of thermodynamics for an isochoric process.
Deduce the first law of thermodynamics for an isochoric process.
Write the mathematical equation of the first law of thermodynamics for the following process:
Isochoric process
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Solution
By substituting equation W = −pex . ΔV in the equation ΔU = q + W, we get
ΔU = q − pex . ΔV ...(1)
If the reaction is carried out in a closed container so that the volume of the system is constant, then Δ = 0. In such a case, no work is involved.
The equation (1) becomes ΔU = qv
Equation (1) suggests that the change in internal energy of the system is due to heat transfer. The subscript v indicates a constant volume process. As U is a state function, qv is also a state function. We see that an increase in the internal energy of a system is numerically equal to the heat absorbed by the system in a constant volume (isochoric) process.
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