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Grade upto college level Thermal Physics

Cp/Cv for monoatomic gas is 1.67 , for diatomic gas is 1.41 , for tri atomic gas is 1.33
What is Cp/Cv when mixed following:-
1. mono & diatomic
2. Diatomic & triatomic
3. triatomic & monoatomic

Profile image of Deepak Patra
12 Years agoGrade upto college level
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1 Answer

Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer1 Year ago

To determine the ratio of specific heats, Cp/Cv, for mixtures of gases, we can use the concept of weighted averages based on the molar fractions of each gas in the mixture. The specific heat capacities for the gases you mentioned are as follows: for monoatomic gases, Cp/Cv is 1.67; for diatomic gases, it is 1.41; and for triatomic gases, it is 1.33. Let's break down the calculations for each mixture step by step.

1. Mixture of Monoatomic and Diatomic Gases

Let's assume we have a mixture of one mole of monoatomic gas and one mole of diatomic gas. The total number of moles in the mixture is 2. The molar fractions are:

  • Monoatomic gas: Xmono = 1/2
  • Diatomic gas: Xdiatomic = 1/2

Now, we can calculate the Cp/Cv for the mixture:

Cp/Cv = Xmono * (Cp/Cv)mono + Xdiatomic * (Cp/Cv)diatomic

Substituting the values:

Cp/Cv = (1/2) * 1.67 + (1/2) * 1.41 = 0.835 + 0.705 = 1.54

2. Mixture of Diatomic and Triatomic Gases

For a mixture of one mole of diatomic gas and one mole of triatomic gas, the total number of moles remains 2, with the following molar fractions:

  • Diatomic gas: Xdiatomic = 1/2
  • Trioatomic gas: Xtriatomic = 1/2

Now, we calculate the Cp/Cv for this mixture:

Cp/Cv = Xdiatomic * (Cp/Cv)diatomic + Xtriatomic * (Cp/Cv)triatomic

Substituting the values:

Cp/Cv = (1/2) * 1.41 + (1/2) * 1.33 = 0.705 + 0.665 = 1.37

3. Mixture of Triatomic and Monoatomic Gases

For a mixture of one mole of triatomic gas and one mole of monoatomic gas, the total number of moles is again 2, with the following molar fractions:

  • Trioatomic gas: Xtriatomic = 1/2
  • Monoatomic gas: Xmono = 1/2

Now, we calculate the Cp/Cv for this mixture:

Cp/Cv = Xtriatomic * (Cp/Cv)triatomic + Xmono * (Cp/Cv)mono

Substituting the values:

Cp/Cv = (1/2) * 1.33 + (1/2) * 1.67 = 0.665 + 0.835 = 1.50

Summary of Results

  • Monoatomic & Diatomic: Cp/Cv = 1.54
  • Diatomic & Triatomic: Cp/Cv = 1.37
  • Trioatomic & Monoatomic: Cp/Cv = 1.50

This method of calculating the specific heat ratio for mixtures is quite useful in thermodynamics, especially when dealing with real-world gas mixtures in various applications. If you have any further questions about this topic or related concepts, feel free to ask!