What is the difference between heterogeneous and homogeneous mixtures? Chemical and physical changes? What is conservation of mass?
Three questions have been posed here. You should ask them 1 at a time.
An homogeneous mixture is where the constituents are in the same phase: i.e. the air we breathe; solutions in a liquid solvent; and metal alloys. In a heterogeneous mixture the constituents are in different phases.
Physical changes are largely changes of state: solid to liquid, liquid to gas etc. Chemical changes involve the formation of new substances and the making and breaking of strong chemical bonds.
And conservation of mass means precisely that! In every chemical reaction that has EVER been performed, if you start with 10 g of reactant from all sources, AT MOST you can 10 g of product.
There are other fuller answers elsewhere. Here is a start.