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QPages 77-80: Q11: HC Verma: Concepts of Physics - Volume 2 Specific Heat Capacities of Gases Pages 77-80: Q11 Solution: Two ideal gases have the same value of . What will be the value …

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often take the mole‑fraction weighted average of the individual $gamma$ values, but $gamma$ is a ratio of heat capacities, not a linear property. Compute $C_{v, ext{mix}}= rac{n_1C_{v1}+n_2C_{v2}}{n_1+n_2}$ and $C_{p, ext{mix}}= rac{n_1C_{p1}+n_2C_{p2}}{n_1+n_2}$ first, then form $gamma_{ ext{mix}}=C_{p, ext{mix}}/C_{v, ext{mix}}$.

Two ideal gases have the same value of Cp/Cv=γC_p / C_v = \gamma. What will be the value of this ratio for a mixture of the two gases in the ratio 1 : 2?

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**Answer:** γmixture=γ\gamma_{mixture} = \gamma. **Step-by-Step Explanation:** For both gases, Cv=Rγ−1C_v = \frac{R}{\gamma-1} and Cp=γRγ−1C_p = \frac{\gamma R}{\gamma-1}. For mixture of n1n_1 and n2n_2 moles:
Cv=n1Cv1+n2Cv2n1+n2=(n1+n2)Rγ−1n1+n2=Rγ−1C_v = \frac{n_1C_{v1} + n_2C_{v2}}{n_1+n_2} = \frac{(n_1+n_2)\frac{R}{\gamma-1}}{n_1+n_2} = \frac{R}{\gamma-1}
Similarly, Cp=γRγ−1C_p = \frac{\gamma R}{\gamma-1}. Hence γmixture=CpCv=γ\gamma_{mixture} = \frac{C_p}{C_v} = \gamma [citation:12].

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