right. the comment about energy in atoms is on the right track. when we say 'freeze' we naturally think of water. heat is lost from the water vapour or water liquid and so the atoms have less energy and so the slow down and form a solid structure. Ice. you can keep cooling this solid i.e. make it colder by taking more heat from it. (there is heat in ice btw, but the atoms are bonded and move less) it is not at absolute zero. we say it is at 0 degrees celcius because that is a convenitent i.e. arbitrary point.) absolute zero is what space is (effectively anyway) and that is a lot colder than ice in your freezer. stuff 'freezes' when it goes solid like water. but also stuff can go solid from forming new bonds i.e. it does not have to be with a loss of heat, it can be exothermic or endothermic reaction. but don't worry about that. we can alter at what temperature something becomes solid by changing the temperature, pressure, adn other things. sea water freezes at lower temperature than fresh water because of the salt.... and the plasic containers thing could be to do with the plastic or the pressure in the containter. oh and also just to confuse you, most things decrease volume when they freeze ie. they take up less space because the atoms/molecules are closer together. BUT water is unusual in that the structure has gaps (where some 'air' is trapped) hence ice is greater volume, less dense and floats in water. so there you go! chemistry is fascinating isn't it?