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Heat and Thermodynamics question

2022 · 28 Jul · Shift 2 · Q60
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Heat and Thermodynamics question

2022 · 28 Jul · Shift 2 · Q60

JEE MainPhysicsHeat and ThermodynamicsNumerical+4 / −1
At a certain temperature, the degrees of freedom per molecule for gas is 8. The gas performs 150 J of work when it expands under constant pressure. The amount of heat absorbed by the gas will be ‾\underline{\hspace{2cm}}​ J.
Numerical answer
View written solutionFree

Correct answer: 750

  1. Use the relation between degrees of freedom and molar heat capacities

For an ideal gas with degrees of freedom fff:

CV=f2RC_V = \frac{f}{2}RCV​=2f​R

and

CP=CV+R=(f2+1)R=f+22RC_P = C_V + R = \left(\frac{f}{2}+1\right)R = \frac{f+2}{2}RCP​=CV​+R=(2f​+1)R=2f+2​R

Given:

f=8f = 8f=8

So,

CP=8+22R=5RC_P = \frac{8+2}{2}R = 5RCP​=28+2​R=5R

  1. Use the work done in constant-pressure expansion

For constant pressure,

W=PΔV=nRΔTW = P\Delta V = nR\Delta TW=PΔV=nRΔT

Given:

W=150 JW = 150\,\text{J}W=150J

Hence,

nRΔT=150nR\Delta T = 150nRΔT=150

  1. Compute heat absorbed at constant pressure

At constant pressure,

Q=nCPΔTQ = nC_P\Delta TQ=nCP​ΔT

Substitute CP=5RC_P = 5RCP​=5R:

Q=n(5R)ΔT=5(nRΔT)Q = n(5R)\Delta T = 5(nR\Delta T)Q=n(5R)ΔT=5(nRΔT)

Using nRΔT=150nR\Delta T = 150nRΔT=150:

Q=5×150=750 JQ = 5 \times 150 = 750\,\text{J}Q=5×150=750J

  1. Final Answer

750\boxed{750}750​

  1. Comparison with stored answer

Stored correct answer = 750750750

This matches the derived answer.

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