Gas

Gases have huge amounts of energy.  When a gas is compressed it is always trying to escape. When you open a soda and you hear they hiss, thats the gas inside escaping. The more a gas is compressed the more energy it has. Think of it like this. If you lock a bunch of people in a room an turn up the heat they will try to get out. When the door opens just a crack they will charge out. Gas will also try to fill up every little space too. They spread all the way out until they fill the container. Gas is warmer than solid and liquids because it has more energy. The less volume a gas has the more pressure it has. The more volume a gas has less pressure. Thats why when you go to higher alitudes its harder to breath.