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The temperature of \(n\) moles of ideal gas is changed from \(T_{1}\) to \(T_{2}\) at constant volume. Show that the corresponding entropy change is \(\Delta S=n C_{V} \ln \left(T_{2} / T_{1}\right)\).

Short Answer

Expert verified
\(\Delta S = nC_v \ln (T2 / T1)\)

Step by step solution

01

Definition of entropy

Recall the differential of entropy, \(dS\), for a reversible process, which is defined as: \(dS = \frac{dq_{rev}}{T}\) where dq_{rev} is the infinitesimal heat transferred in a reversible process and T is the absolute temperature.
02

Expression of heat in terms of specific heat

The amount of heat, \(dq_{rev}\), for an ideal gas at constant volume, is given by \(dq_{rev} = nC_v dT\). Here, \(C_v\) is the molar specific heat at constant volume, dT is the infinitesimal change in temperature and n is the number of moles of gas.
03

Plug \(dq_{rev}\) into the entropy equation

Substitute \(dq_{rev} = nC_v dT\) into the equation from step 1 to get: \(dS = \frac{nC_v dT}{T}\)
04

Integrate both sides to find the entropy change

Integrating both sides from \(T1\) to \(T2\) gives the total change in entropy, \(\Delta S = nC_v \int_{T1}^{T2} \frac{dT}{T}\). Solving the integral on the right side yields: \(\Delta S = nC_v \ln (T2 / T1)\)

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Most popular questions from this chapter

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