R is the ideal gas constant: the energy per mole per kelvin. It equals Avogadro's number times the Boltzmann constant, R = Nₐk.
Value of R in different units
| Value | Use it when |
|---|---|
| 8.314 J mol⁻¹ K⁻¹ | SI. Use with energy in joules (ΔG = −RT ln K, Arrhenius). |
| 0.0821 L atm mol⁻¹ K⁻¹ | PV = nRT with P in atm and V in litres. |
| 0.08314 L bar mol⁻¹ K⁻¹ | PV = nRT with P in bar. |
| 1.987 ≈ 2 cal mol⁻¹ K⁻¹ | Thermochemistry in calories. |
| 8.314 × 10⁷ erg mol⁻¹ K⁻¹ | CGS units. |
| 62.36 L mmHg mol⁻¹ K⁻¹ | Pressure in mmHg or torr. |
Formulas that use R
- PV = nRT
- ΔG° = −RT ln K = −2.303 RT log K
- k = A e^(−Eₐ/RT)
- Cₚ − Cᵥ = R
- vᵣₘₛ = √(3RT/M)
Its dimensional formula is worked out on the dimensional formula of universal gas constant R page.
Other constants
- Gas constant (R): 8.314 J mol⁻¹ K⁻¹
- Planck's constant (h): 6.626 × 10⁻³⁴ J s
- Avogadro's number (Nₐ): 6.022 × 10²³ mol⁻¹
- Speed of light (c): 3 × 10⁸ m/s
- Charge of an electron (e): 1.602 × 10⁻¹⁹ C
- Mass of an electron (mₑ): 9.109 × 10⁻³¹ kg
- Mass of a proton (mₚ): 1.673 × 10⁻²⁷ kg
- Mass of a neutron (mₙ): 1.675 × 10⁻²⁷ kg
- Universal gravitational constant (G): 6.674 × 10⁻¹¹ N m² kg⁻²
- Acceleration due to gravity (g): 9.8 m/s²
- Boltzmann constant (k): 1.381 × 10⁻²³ J/K
- Faraday constant (F): 96 485 C/mol
- Permittivity of free space (ε₀): 8.854 × 10⁻¹² C² N⁻¹ m⁻²
- Permeability of free space (μ₀): 4π × 10⁻⁷ T m/A
- Rydberg constant (R): 1.097 × 10⁷ m⁻¹
- Stefan–Boltzmann constant (σ): 5.67 × 10⁻⁸ W m⁻² K⁻⁴
- Wien's constant (b): 2.898 × 10⁻³ m K
- Bohr radius (a₀): 0.529 Å
- Molar volume of a gas at STP (Vₘ): 22.4 L/mol
The full list, searchable, is on the physical constants page.
Questions students ask
What is the value of gas constant?
R = 8.314 J mol⁻¹ K⁻¹. In other units: 8.314 J mol⁻¹ K⁻¹; 0.0821 L atm mol⁻¹ K⁻¹; 0.08314 L bar mol⁻¹ K⁻¹; 1.987 ≈ 2 cal mol⁻¹ K⁻¹; 8.314 × 10⁷ erg mol⁻¹ K⁻¹; 62.36 L mmHg mol⁻¹ K⁻¹.
What is R in physics and chemistry?
R is the ideal gas constant: the energy per mole per kelvin. It equals Avogadro's number times the Boltzmann constant, R = Nₐk.
Which value of R should I use?
8.314 J mol⁻¹ K⁻¹: SI. Use with energy in joules (ΔG = −RT ln K, Arrhenius). 0.0821 L atm mol⁻¹ K⁻¹: PV = nRT with P in atm and V in litres. 0.08314 L bar mol⁻¹ K⁻¹: PV = nRT with P in bar. 1.987 ≈ 2 cal mol⁻¹ K⁻¹: Thermochemistry in calories. 8.314 × 10⁷ erg mol⁻¹ K⁻¹: CGS units. 62.36 L mmHg mol⁻¹ K⁻¹: Pressure in mmHg or torr.
What is the dimensional formula of gas constant?
See the dimensional formula of gas constant, worked out step by step on its own page.