Chemistry Gases MDCAT 2017
PMDC Verified Question 58 of 65
Identify the value of R at STP.
A
\( 8.314 \text{ atm dm}^3 \text{ mol}^{-1} \)
B
\( 0.0821 \text{ atm dm}^3 \text{ K}^{-1} \text{ mol}^{-1} \)
C
\( 0.0821 \text{ cal K}^{-1} \text{ mol}^{-1} \)
D
\( 8.314 \text{ cal K}^{-1} \text{ mol}^{-1} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( 0.0821 \text{ atm dm}^3 \text{ K}^{-1} \text{ mol}^{-1} \)
Concept:

The universal gas constant (R) is derived from the ideal gas equation \( R = \frac{PV}{nT} \). Its numerical value depends entirely on the units used for Pressure (P) and Volume (V).

Solution:

  • At Standard Temperature and Pressure (STP), \( P = 1 \text{ atm} \), \( T = 273.15 \text{ K} \), and for \( n = 1 \text{ mole} \), \( V = 22.414 \text{ dm}^3 \).


  • Substitute these into the equation: \( R = \frac{1 \text{ atm} \times 22.414 \text{ dm}^3}{1 \text{ mole} \times 273.15 \text{ K}} \).


  • Calculating this yields \( R \approx 0.0821 \text{ atm dm}^3 \text{ K}^{-1} \text{ mol}^{-1} \).


Why other options are incorrect:

  • Option A: 8.314 is the value of R in SI units (Joules), and the unit provided lacks Kelvin \( (\text{K}^{-1}) \).
  • Options C & D: The value of R in calories is approximately \( 1.987 \text{ cal K}^{-1} \text{ mol}^{-1} \), making these combinations incorrect.

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.

Previous Question All Gases MCQs Next Question

Want to solve full-length papers under timed exam conditions?

Practice with zero-scroll lockdown sprints, dynamic latency zone timers, live peer selection telemetry, and the automated Amber mistake recovery loop.

Enter Arena Sprint iOS App Android App