The ideal gas law
One equation ties together the four quantities that describe a gas.
P × V = n × R × T
| Symbol | Quantity | Unit |
|---|---|---|
| P | Pressure | atm |
| V | Volume | L |
| n | Amount | mol |
| T | Temperature | K |
| R | Gas constant | 0.08206 L·atm/(mol·K) |
The units must match the units of R. Convert before calculating.
An ideal gas is a model in which particles have no volume and do not attract each other. Real gases follow it closely at ordinary temperatures and pressures, and less well at high pressure or low temperature.
Worked example: volume of 1.00 mol of gas at STP
At STP, T = 273 K and P = 1.00 atm. Solve for V.
V = n × R × T ÷ P
V = 1.00 mol × 0.08206 L·atm/(mol·K) × 273 K ÷ 1.00 atm = 22.4 L
One mole of any ideal gas occupies 22.4 L at STP.
Common mistake
Leaving the temperature in Celsius or the volume in milliliters. With R = 0.08206, pressure must be in atm, volume in L and temperature in K.