Is expansion a physical or chemical property?

Expansion of a material is a physical property. A physical property is one that can be observed and is related to a physical change. A chemical property, on the other hand, is one that is observed through a chemical reaction and is thus, related to chemical change. 

Expansion is typically observed during heating of material. For example, when we heat a bar of metal (say iron), it expands. We can also blow air into a...

Expansion of a material is a physical property. A physical property is one that can be observed and is related to a physical change. A chemical property, on the other hand, is one that is observed through a chemical reaction and is thus, related to chemical change. 

Expansion is typically observed during heating of material. For example, when we heat a bar of metal (say iron), it expands. We can also blow air into a balloon and observe its expansion. In both such cases, the material remains the same and no chemical change or reaction takes place. The chemical composition of the materials (metal and balloon) remains the same, the only change is the intermolecular spacing. Hence expansion is a physical property and not a chemical property.

Hope this helps.