What causes matter to change states?
What type of change causes a difference in the look of matter but the molecules that make up the matter stay the same?
Explain how a change in thermal energy causes matter to change from one state to another give two examples?
You are confusing the law of conservation of matter/mass with the law of conservation of energy. The law of conservation of matter/mass states that in a closed system matter is neither created nor destroyed. During a chemical reaction matter is rearranged, it doesn't change forms (energy can change forms). The atoms in the products are the same atoms that were in the reactants.