Question

What is the constant in ideal gas equation known as?

(a) Universal gas constant

(b) Pressure constant

(c) Temperature constant

(d) Boltzmann constant

I got this question during an internship interview.

My enquiry is from States of Matter topic in portion States of Matter of Chemistry – Class 11

Answer 1

The constant in the ideal gas equation is known as the:

(a) Universal gas constant

Explanation:

The ideal gas equation is:

$$PV=nRT$$

Here:

• $P$ = pressure,
• $V$ = volume,
• $n$ = number of moles,
• $R$ = universal gas constant,
• $T$ = temperature.

The universal gas constant ($R$) has a fixed value in the SI system:

R=8.314 J mol−1K−1R = 8.314 \, \text{J mol}^{-1} \text{K}^{-1}R=8.314J mol−1K−1

It serves as a proportionality constant that relates the variables of pressure, volume, temperature, and amount of gas in the equation. Its value can also be expressed in other units depending on the context, such as 0.0821 L atm mol−1K−10.0821 \, \text{L atm mol}^{-1} \text{K}^{-1}0.0821L atm mol−1K−1.

Incorrect Options:

• (b) Pressure constant: No such specific term exists.
• (c) Temperature constant: This is not related to $R$.
• (d) Boltzmann constant: While related, it is different. Boltzmann constant ($k$) is R/NAR/N_AR/NA​, where NAN_ANA​ is Avogadro's number.

Thus, the correct answer is (a) Universal gas constant.