This document discusses the different states of matter and the changes between them. It explains that solids have a definite shape and volume due to the tight packing and vibration of particles. Liquids can change shape but not volume as their particles can slide past one another. Gases expand to fill their containers since particles are far apart and move independently. Changes between solid, liquid and gas require the addition or removal of energy to overcome or increase intermolecular forces. Temperature represents the average kinetic energy of particles but changes in temperature only occur once a change of state is complete.