Is a change of the state (or phase) of matter a physical or chemical change?
A phase change does not involve changing the identity or makeup of that species. When you take solid ice and melt it (add enough energy to it) it changes to water, which is now a liquid. It's still water because if you could see at the atomic level, you would still see
A chemical change would involve reactions taking place that would change the whole identity of that species. If you took two beakers of different compounds and mixed them, you would get out something totally different (Acid-base reaction, let's say, to get salt and water).
Kind of like when you get a haircut. If you grow your hair out to a decent length, and then the next day you wake up and decide you want a buzz cut, you are still the same person; you just might look a little different. But, you haven't changed who you are as Billy, Bob, or Joe.