On Sat, Oct 25, 2014 at 3:27 AM, Jed Rothwell <jedrothw...@gmail.com> wrote:
> H Veeder <hveeder...@gmail.com> wrote: > > >> Scott Little showed a beautiful example of this once. He put a >>> rechargeable battery into a calorimeter and charged it up. There was a >>> deficit comparing electricity to the rising temperature. Then he discharged >>> the battery through a resister in the cell. All the lost energy came back. >>> The balance was close to zero. >>> >>> >> >> Was the temperature of the water in the calorimeter rising during >> charging? >> > > I don't recall. It was a long time ago. Anyway, it was less than it would > have been if all the electricity had converted to heat. Some of it did > convert convert to heat, but there was a deficit. > > - Jed > > Unless heat is absorbed during charging and is released during discharge a calorimeter can't tell you if an endothermic reaction occurred. You also need a-priori knowledge of how the energy is stored. The calorimeter by itself only tells you that there was a mildly exothermic reaction followed by more intense exothermic reaction. Charging a battery is endothermic because it absorbs *electrical* energy, not because it absorbs *heat* energy. If a calorimeter were good at detecting all types of endothermic reactions then you could substitute them for volt meters. Heat is a form of energy and although energy cannot be destroyed (according to CoE principle) heat can be destroyed by converting it into another form of energy. Note that the terms endothermic and exothermic are used in a way that supersedes their original meaning of absorbing or releasing *heat*. Harry
