Are reactions with water to form a gas physical or chemical changes?
In your scenario, a material reacts with water to form a gas. I can think of a couple of actual examples which are manifestly examples of chemical change:
So here strongish metal-metal and stronger
Physical changes are largely changes of state, i.e. solid to liquid to gas, in which the phase of the material has changed, but the intrinsic chemical bond have is unaltered: cf water to ice, the