Units for Pressure, Volume, and Temperature in the Ideal Gas Law
Pressure (P)
Pressure is the force exerted by gas particles when they collide with the walls of their container.
Common units:
- atmospheres (atm) — standard unit used with
R = 0.0821 L·atm/mol·K - pascals (Pa) or kilopascals (kPa) — used with
R = 8.314 J/mol·K - millimeters of mercury (mmHg) or torr — 1 atm = 760 mmHg = 760 torr
Volume (V)
Volume represents the amount of space a gas occupies.
Standard unit:
- liters (L) — used in most gas law problems with
R = 0.0821 - Sometimes expressed in cubic meters (m³) in SI units (1 m³ = 1000 L)
Temperature (T)
Temperature reflects the average kinetic energy of gas particles.
Required unit:
- Kelvin (K) — always used in the ideal gas law
Important: Celsius or Fahrenheit must be converted to Kelvin:
K = °C + 273.15
Note on Consistency
The gas constant R must match the units used for pressure and volume. For example:
R = 0.0821 L·atm/mol·K→ use atm, L, and KR = 8.314 J/mol·K→ use Pa, m³, and K