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Heat and Thermodynamics question

2025 · 28 Jan · Shift 2 · Q67
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Heat and Thermodynamics question

2025 · 28 Jan · Shift 2 · Q67

JEE MainPhysicsHeat and ThermodynamicsMCQ+4 / −1
The kinetic energy of translation of the molecules in 50 g of CO2\text{CO}_2CO2​ gas at 17°C is :
  1. A
    4205.5 J
  2. B
    3582.7 J
  3. C
    3986.3 J
  4. D
    4102.8 J
View written solutionFree

Correct answer: D

  1. Use the formula for translational kinetic energy of an ideal gas

For all molecules of an ideal gas, the total kinetic energy of translation is

K=32nRTK = \frac{3}{2} nRTK=23​nRT

where:

  • nnn = number of moles
  • R=8.314 J mol−1K−1R = 8.314\ \text{J mol}^{-1}\text{K}^{-1}R=8.314 J mol−1K−1
  • TTT = absolute temperature

  1. Calculate number of moles of CO2\text{CO}_2CO2​

Given mass of CO2\text{CO}_2CO2​:

m=50 gm = 50\ \text{g}m=50 g

Molar mass of CO2\text{CO}_2CO2​:

M=44 g mol−1M = 44\ \text{g mol}^{-1}M=44 g mol−1

So,

n=mM=5044=1.13636 moln = \frac{m}{M} = \frac{50}{44} = 1.13636\ \text{mol}n=Mm​=4450​=1.13636 mol


  1. Convert temperature into kelvin

T=17∘C+273=290 KT = 17^{\circ}\text{C} + 273 = 290\ \text{K}T=17∘C+273=290 K

(Using 290 K290\,\text{K}290K is standard here.)


  1. Substitute into the formula

K=32×5044×8.314×290K = \frac{3}{2} \times \frac{50}{44} \times 8.314 \times 290K=23​×4450​×8.314×290

First compute:

8.314×290=2411.068.314 \times 290 = 2411.068.314×290=2411.06

Then,

5044×2411.06=2739.84\frac{50}{44} \times 2411.06 = 2739.844450​×2411.06=2739.84

Now,

K=32×2739.84=4109.76 JK = \frac{3}{2} \times 2739.84 = 4109.76\ \text{J}K=23​×2739.84=4109.76 J

Using the common approximation R=8.31R = 8.31R=8.31:

K=32×5044×8.31×290K = \frac{3}{2} \times \frac{50}{44} \times 8.31 \times 290K=23​×4450​×8.31×290

=4108.28 J= 4108.28\ \text{J}=4108.28 J

This is closest to Option D.


  1. Check options
  • A: 4205.5 J4205.5\,\text{J}4205.5J — not matching
  • B: 3582.7 J3582.7\,\text{J}3582.7J — too low
  • C: 3986.3 J3986.3\,\text{J}3986.3J — not matching
  • D: 4102.8 J4102.8\,\text{J}4102.8J — closest and correct by standard rounding/approximation

  1. Final answer

The kinetic energy of translation of the molecules is

4102.8 J (approximately)\boxed{4102.8\ \text{J} \text{ (approximately)}}4102.8 J (approximately)​

So the correct option is D.

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