An ideal gas is a theoretical gas componed o mony randomly muivin pynt pairticles that dinna interact except when thay collide elastically. The ideal gas concept is uisefu acause it obeys the ideal gas law, a simplified equation o state, an is amenable tae analysis unner stateestical mechanics. Ane mole o an ideal gas haes a volume o 22.4 litres at STP as defined bi IUPAC.