Physics Thermodynamics PMDC 2021
PMDC Verified Question 44 of 54
\(C_p - C_v\) value, find if 3 moles of gas is given
A
7R
B
5R
C
2R
D
3R
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 3R
1. Concept:

The difference between the total heat capacity at constant pressure and constant volume for 'n' moles of an ideal gas equals \(nR\).

2. Formula:

$$C_p - C_v = nR$$

3. Solution:

  • The standard molar specific heat relation is \(c_p - c_v = R\) (for 1 mole).


  • The question refers to the total heat capacities \(C_p\) and \(C_v\) for 3 moles of the gas.


  • By substituting \(n = 3\) into the extensive property relation, we get \(C_p - C_v = 3R\).


4. Why other options are incorrect:

Options like 2R, 5R, or 7R are purely distractor values and do not map to the number of moles provided in the question stem.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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