Gas Density
The mass of a gas per unit volume, which for a gas depends strongly on temperature, pressure and molar mass.
Formula / equation
ρ = pM / RT
Unit
g/L
In depth
Because gas density is directly proportional to molar mass at fixed conditions, measuring it is a straightforward route to identifying an unknown gas. Density falls as temperature rises, which drives convection currents and makes hot-air balloons rise.
Examples in the real world
Air is 1.29 g/L at STP, helium only 0.18 g/L, and sulfur hexafluoride a hefty 6.6 g/L.