What is a change in the properties of matter that does not change the the identity of the substance?
physical changes, like changing state.
a physical change does change the identity of a substance.
physical changes are things like, changing states - so melting solids to liquids or boiling liquids to gases. All that you are doing is altering how the particles are arranged - you are not actually altering the particles themselves.
As a common example, if you freeze water it becomes ice - it is still water, but in solid form. Or if you boil water it becomes water vapour, it is still water.