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JEE Main
Exam
JEE Main
Subject
Physics
Chapter
Kinetic Theory of Gases

JEE Main · Physics · Kinetic Theory of Gases

A gas mixture contains n_1 moles of a monoatomic gas and n_2 moles...

A gas mixture contains n1n_1 moles of a monoatomic gas and n2n_2 moles of gas of rigid diatomic molecules. Each molecule in monoatomic and diatomic gas has 3 and 5 degrees of freedom respectively. If the adiabatic exponent (CpCV)\left(\frac{C_p}{C_V}\right) for this gas mixture is 1.5 , then the ratio n1n2\frac{n_1}{n_2} will be

Options

  1. A1
  2. B1.5
  3. C2
  4. D2.5

Correct answer

A. 1

Step-by-step solution

For a gas mixture, C_V=n1CV1+n2CV2n1+n2 and \frac{n_1 C_{V_1}+n_2 C_{V_2}}{n_1+n_2} \text { and }C_p=n1Cp1+n2Cp2n1+n2\frac{n_1 C_{p_1}+n_2 C_{p_2}}{n_1+n_2}For monoatomic gas, n=n_1, C_{V_1}=32\frac{3}{2}R, \quad C_{p_1}=52\frac{5}{2}R For diatomic gas, n=n_2, C_{V_2}=52\frac{5}{2}R  and \text { and }C_{p_2}=72\frac{7}{2}R Now given for gas mixture, CpCV=1.5 So, 1.5=n1n2(52)+72n1n2(32)+5292(n1n2)+152=(n1n2)5+7⇒n1n2=1\begin{gathered} \quad\frac{C_p}{C_V}=1.5 \\ \text { So, }1.5=\frac{\frac{n_1}{n_2}\left(\frac{5}{2}\right)+\frac{7}{2}}{\frac{n_1}{n_2}\left(\frac{3}{2}\right)+\frac{5}{2}} \quad \frac{9}{2} \left(\frac{n_1}{n_2}\right)+\frac{15}{2}=\left(\frac{n_1}{n_2}\right)5+7 \\ \Rightarrow \frac{n_1}{n_2}=1 \end{gathered}
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