Question

Is water freezing to ice endothermic or exothermic? Natural gas burning?

Answer 1

Well, you are making bonds, so we would assume ice formation to be exothermic.....

Explanation:

`H_2O(l) rarr H_2O(s) + Delta`

When natural gas is burned, the reaction is much less ambiguous. Strong `C=O` and `H-O` bonds are formed, which are stronger than the `C-H` and `O=O` bonds that are broken:

`CH_4(g) + O_2(g) rarr CO_2(g) + 2H_2O(l) + Delta`

This reaction is appreciably and measurably exothermic, and is probably heating your home right now (well it would be if you live in the northern hemisphere).