Beginner Topic 233 of 1102 States of Matter & Solutions
Gas Constant
The universal constant R equals 8.314 J per mole per kelvin or 0.0821 L atm per mole per kelvin.
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In-depth explanation of Gas Constant
The gas constant R is the proportionality constant in the ideal gas law and sets the energy scale per mole per kelvin. It equals the product of Avogadro's number and the Boltzmann constant, R = NA kB, where kB is 1.381 × 10^-23 J/K. Its numerical value depends on the units used: 8.314 J mol^-1 K^-1 when energy is in joules, or 0.08206 L atm mol^-1 K^-1 when pressure is in atmospheres and volume in litres. Since 1 kPa L equals 1 J, the value 8.314 kPa L mol^-1 K^-1 is also correct. Always choose the value whose units match the pressure and volume units in the problem.
Going deeper: Gas Constant
Key ideas: R = 8.314 J/(mol K) = 8.314 Pa m3/(mol K) = 0.08206 L atm/(mol K) = 62.36 L torr/(mol K) = 1.987 cal/(mol K). The same R appears in the Nernst equation, Arrhenius equation, entropy, and osmotic pressure. The value per molecule is the Boltzmann constant, 1.381 x 10^-23 J/K.
Common mistakes and connections: A frequent mistake is picking 8.314 and then using pressure in atmospheres and volume in litres. Another is thinking R changes between gases; it is universal. Specific gas constant R_specific equals R divided by molar mass, used in engineering but not in typical chemistry problems. Ties to PV = nRT, kinetic energy and equilibrium thermodynamics.
Visualization of Gas Constant
R equals N_A times k_B and takes different numerical values depending on units; pick the one matching your pressure and volume units. The interactive lesson shows this as a live animation or chart.
Worked example and use case
With pressure in kPa and volume in litres, use R = 8.314 kPa L mol^-1 K^-1.
Frequently asked questions about Gas Constant
What is Gas Constant?
The universal constant R equals 8.314 J per mole per kelvin or 0.0821 L atm per mole per kelvin.
Is Gas Constant a beginner, intermediate or advanced topic?
Gas Constant is a beginner topic in States of Matter & Solutions. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Gas Constant?
Study these earlier topics in States of Matter & Solutions first: Avogadro's Law, Combined Gas Law, Ideal Gas Law.
What comes after Gas Constant?
The next topics in States of Matter & Solutions are Absolute Zero and Dalton's Law of Partial Pressures.
Can I practise Gas Constant with quizzes?
Yes. The interactive lesson includes a self-check question on Gas Constant, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Gas Constant fits in States of Matter & Solutions
Gas Constant is topic 14 of 109 in States of Matter & Solutions.