I believe it does. If you have a bottle full of chemicals with potential energy, and then you make them react and get the energy from them (via, I dunno, heat)

I believe it does. If you have a bottle full of chemicals with potential energy, and then you make them react and get the energy from them (via, I dunno, heat), while all the particles remain in the bottle, then I think the bottle weighs less afterwards—though probably by an undetectably small amount. I think I read that the change in mass is detectable after, say, nuclear fission.