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Ch 20: The Micro/Macro Connection
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Non è quello che usi tu?Cambia libro di testo
Capitolo 20, Problema 69a

n1 moles of a monatomic gas and n2 moles of a diatomic gas are mixed together in a container. Derive an expression for the molar specific heat at constant volume of the mixture.

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Step 1: Recall the molar specific heat at constant volume (Cᵥ) for a monatomic gas and a diatomic gas. For a monatomic gas, Cᵥ₁ = (3/2)R, and for a diatomic gas, Cᵥ₂ = (5/2)R, where R is the universal gas constant.
Step 2: Understand that the molar specific heat of the mixture is a weighted average based on the number of moles of each type of gas. Let n₁ be the moles of the monatomic gas and n₂ be the moles of the diatomic gas.
Step 3: Write the total heat capacity of the mixture at constant volume as the sum of the contributions from each gas: Cᵥ_total = n₁Cᵥ₁ + n₂Cᵥ₂.
Step 4: Divide the total heat capacity by the total number of moles (n₁ + n₂) to find the molar specific heat of the mixture: Cᵥ_mixture = (n₁Cᵥ₁ + n₂Cᵥ₂) / (n₁ + n₂).
Step 5: Substitute the values of Cᵥ₁ and Cᵥ₂ into the expression: Cᵥ_mixture = (n₁(3/2)R + n₂(5/2)R) / (n₁ + n₂). Simplify the expression to derive the final formula for the molar specific heat at constant volume of the mixture.

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Molar Specific Heat Capacity

Molar specific heat capacity is the amount of heat required to raise the temperature of one mole of a substance by one degree Celsius at constant volume. For gases, this value varies depending on the type of gas; monatomic gases typically have a specific heat of 3/2 R, while diatomic gases have a specific heat of 5/2 R, where R is the universal gas constant.
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Specific Heat & Temperature Changes

Mixing of Gases

When different gases are mixed, the total specific heat capacity of the mixture can be calculated as a weighted average based on the number of moles of each gas. This involves considering the contributions of each gas's specific heat capacity and the respective moles present in the mixture, allowing for the derivation of an overall expression for the mixture's specific heat.
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Internal Energy of Ideal Monoatomic Gases

Constant Volume Process

In a constant volume process, the volume of the gas does not change, meaning that any heat added to the system results in a change in temperature rather than work done by the gas. This condition is crucial for deriving the molar specific heat at constant volume, as it simplifies the relationship between heat transfer, temperature change, and specific heat capacity.
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Phase Constant of a Wave Function
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E1f=3n13n1+5n2(E1i+E2i)E2f=5n23n1+5n2(E1i+E2i)\(\begin{aligned}\) E_{1f} &= \(\frac{3n_1}{3n_1 + 5n_2}\) (E_{1i} + E_{2i}) \\ E_{2f} &= \(\frac{5n_2}{3n_1 + 5n_2}\) (E_{1i} + E_{2i}) \(\end{aligned}\)

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