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Heat and Thermodynamics question

2024 · 27 Jan · Shift 2 · Q77
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Heat and Thermodynamics question

2024 · 27 Jan · Shift 2 · Q77

JEE MainPhysicsHeat and ThermodynamicsMCQ+4 / −1
The total kinetic energy of 1 mole of oxygen at 27∘C27^{\circ} \mathrm{C}27∘C is : [Use universal gas constant (R)=8.31 J/(R)=8.31 \mathrm{~J} /(R)=8.31 J/ mole K]
  1. A
    6232.5 J
  2. B
    5670.5 J
  3. C
    6845.5 J
  4. D
    5942.0 J
View written solutionFree

Correct answer: A

  1. Use the kinetic theory result

For an ideal gas, the total translational kinetic energy of nnn moles is

K=32nRTK = \frac{3}{2}nRTK=23​nRT

Here,

  • n=1n = 1n=1 mole
  • R=8.31 J mol−1K−1R = 8.31\,\text{J mol}^{-1}\text{K}^{-1}R=8.31J mol−1K−1
  • T=27∘C=300 KT = 27^\circ \text{C} = 300\,\text{K}T=27∘C=300K
  1. Substitute the values

K=32(1)(8.31)(300)K = \frac{3}{2}(1)(8.31)(300)K=23​(1)(8.31)(300)

  1. Calculate step-by-step

First,

8.31×300=24938.31 \times 300 = 24938.31×300=2493

Then,

K=32×2493=1.5×2493=3739.5 JK = \frac{3}{2} \times 2493 = 1.5 \times 2493 = 3739.5\,\text{J}K=23​×2493=1.5×2493=3739.5J

  1. But this value is not among the options

So the question is likely asking for the total kinetic energy of all degrees of freedom of oxygen molecules.

Since oxygen is a diatomic gas, at ordinary temperature its molar kinetic energy is

K=52nRTK = \frac{5}{2}nRTK=25​nRT

(because it has 3 translational and 2 rotational degrees of freedom).

  1. Now calculate using 52RT\frac{5}{2}RT25​RT

K=52(1)(8.31)(300)K = \frac{5}{2}(1)(8.31)(300)K=25​(1)(8.31)(300)

K=2.5×2493=6232.5 JK = 2.5 \times 2493 = 6232.5\,\text{J}K=2.5×2493=6232.5J

  1. Match with the options

6232.5 J6232.5\,\text{J}6232.5J

This corresponds to Option A.


Final Answer

Option A: 6232.5 J6232.5\,\text{J}6232.5J

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