Gas constant
Definition and meaning of Gas constant in chemistry.
The gas constant (R) is the proportionality constant that links pressure, volume, temperature, and amount of substance for one mole of an ideal gas, appearing in the ideal gas law PV = nRT.
In more detail
It equals the product of Avogadro's number and the Boltzmann constant (R = N_A·k_B), scaling the per-particle energy-temperature relationship up to a per-mole basis. Because pressure and volume can be expressed in different unit systems, R takes different numerical values depending on the units chosen, though the underlying physical quantity is the same. Since the 2019 SI redefinition, both N_A and k_B are exact defined constants, making R an exactly defined value in SI units. R also appears in related expressions, including the van der Waals equation and the Arrhenius equation.
Key facts
| Symbol | R |
|---|---|
| SI Value | 8.314 J/(mol·K) |
| Alternate Value | 0.08206 L·atm/(mol·K) |
| Field | Physical Chemistry |
For 1.00 mol of an ideal gas at standard temperature and pressure (0 °C, 1 atm), the ideal gas law gives V = nRT/P = (1.00 mol)(0.08206 L·atm/mol·K)(273.15 K)/(1.00 atm) = 22.4 L, the familiar molar volume of an ideal gas at STP.
Frequently asked questions
What is the value of the gas constant in different units?
Common values include 8.314 J/(mol·K), 0.08206 L·atm/(mol·K), and 62.36 L·torr/(mol·K); all represent the same physical constant expressed with different pressure and volume units.
How is the gas constant related to the Boltzmann constant?
R equals Avogadro's number multiplied by the Boltzmann constant (R = N_A·k_B), converting the per-particle Boltzmann constant into a per-mole quantity.