Is making glue an example ot a chemical change or a physical change? How do you know?

You said “making glue” so I assume you mean the process of preparing a glue formulation, rather than using the glue to stick something together. Some glues are simply solutions of a substance (polymer for example) in a solvent, others may require some sort of chemical reaction, so you would need to specify exactly how the glue is made.

However, in general terms if a change results in no different chemical species being created (no chemical bonds being broken or formed), then it’s a physical change. If any chemical reaction occurs so that new chemical species are formed, then it’s a chemical change.

Please note: designation of chemical or physical change is NOT related to reversibility.

Because the process of making glue usually entails combining different substances to form a new compound that has different properties from the original substances, it is an example of an irreversible chemical change because the glue cannot be readily separated back into its original components. Moreover, the formation of the glue involves the breaking and forming of chemical bonds, which is a characteristic of a chemical change.