JEE Main & Advanced Physics Kinetic Theory of Gases Question Bank Self Evaluation Test - Kinetic Theory

  • question_answer
    The average translational energy and the rms speed of molecules in a sample of oxygen gas at 300 K are \[6.21\text{ }\times \text{ }{{10}^{-21}}\text{ }J\] and 484 m/s respectively The corresponding values at 600 K are nearly (assuming ideal gas behavior)

    A) \[12.42\times {{10}^{-21}}J,928m/s\]

    B) \[8.78\times {{10}^{-21}}J,684m/s\]

    C) \[6.21\times {{10}^{-21}}J,968m/s\]

    D) \[12.42\times {{10}^{-21}}J,684m/s\]

    Correct Answer: D

    Solution :

    [d] The formula for average kinetic energy is \[\overline{\text{K}\text{.E}\text{.}}=\frac{3}{2}kT\text{ }\therefore \frac{{{\left( \overline{\text{K}\text{.E}\text{.}} \right)}_{600K}}}{{{\left( \overline{\text{K}\text{.E}\text{.}} \right)}_{300K}}}=\frac{600}{300}\]  \[\Rightarrow {{(\overline{\text{K}\text{.E}\text{.}})}_{600K}}=2\times 6.21\times {{10}^{-21}}J\]             \[=\,12.42\,\times {{10}^{-21}}\,J\] Also the formula for r.m.s. velocity is \[{{C}_{rms}}=\sqrt{\frac{3KT}{m}}\therefore \frac{{{\left( {{C}_{rms}} \right)}_{600K}}}{{{\left( {{C}_{rms}} \right)}_{300K}}}=\sqrt{\frac{600}{300}}\] \[\Rightarrow {{({{C}_{rms}})}_{600K}}=\sqrt{2}\times 484=684m/s\]


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