Exothermic epithany in Grange

With Epithany a few days away, here's the Nativity display in Grange-over-Sands. It's been a good year for knitting. We found some lovely guerilla knitting in Seascale in the summer. I'm still thinking about the Physics of knitting! But note the white pot in the corner of the display case in the picture. It will contain something like anhydrous calcium chloride to absorb water vapour from the air and thus stop condensation on the glass. The absorption is an exothermic reaction. It needs some activation energy from somewhere but then the reaction is just like falling over. The chemicals go from a higher energy state to a lower energy state. Potential is lost and is transferred as thermal energy. Potential is usually given a negative number in Physics, This is why I was confused a few years ago when I had my class adding up bond energies for such a reaction. The products' bond energies were bigger than those of the reactants. I realised that you could only claim lower potential energy if the energy was given a negative sign.