Gases
Lowest density, highest energy form
Individual molecules or atoms in a gas are disordered
Molecules or atoms collide with others or the walls of container to produce a measurable pressure
On condensing, gas shrinks by a factor of about 1000
Volume of liquid condensate is ~1/1000th volume of gas
Condensing gases give off heat (²H of condensation), even though the temperature remains constant
Liquids have lower internal energy than the corresponding gas