[user3869]

I am trying to create an exothermic reaction by mixing CaO and H2O.
I purchased CaO from several sources online and much to my chagrin, they produce no heat when mixed with water. Is there something I am missing, or are the materials they sent me not actually CaO?
The materials very specifically say CaO, "non-slaked lime", "non-hydrated lime", "not calcium hydroxide", etc.

Is there any way I can test if the materials are actually CaO? Are there any additives that would make the reaction more exothermic? I have read that adding powdered aluminum or sodium carbonate would help, but I thought that CaO and water on its own should release a measurable amount of heat energy.

[Arkcon]

Adding just a little bit of water to lime should generate some heat, although I don't know if you really get the huge amounts (enough to cook food) that you hear about on gee-wiz internet sites.  You seem to be using the correctly named stuff, slaked or hydrated lime is what you get after you wet lime.  Maybe it was exposed to water already.  Tell us how you're doing thins: how much lime to how much water in what sort of space.

[Borek]

If it was left in the open it could absorb some water and some carbon dioxide. It can mean the exposed surface is already covered with calcium carbonate and calcium hydroxide, slowing the reaction.