Would a change in shape or phase be both a physical and chemical change?

no only physical

Explanation:

for both of those their chemical properties do not change but their physical properties do making them physical changes

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.