The reaction is used to make quick lime, which is an industrially important product.
Equipment used by Priestley in his experiments on gases
Some oxides, especially of weakly electropositive metals decompose when heated to high enough temperatures. A classical example is the decomposition of mercuric oxide to give oxygen and mercury metal. The reaction was used by Joseph Priestley to prepare samples of gaseous oxygen for the first time, leading Antoine Lavoisier to explore they have cooled to a comfortable temperature. Once they start to char, such dishes commonly will continue in a positive feedback loop; they become dangerously hot and continue to blacken from the inside out, and continue to produce smoke even well after being removed from the heat. In films, where stuntmen have to jump through breaking windows, the window panes traditionally were breakaway glass made of sugar, which is safer than real glass. Melting the sugar is a tricky business, however; an error of just a few degrees will start a caramelisation process that will ruin the product, so nowadays suitable plastics are commonly used instead.
When water is heated to well over 2000 °C, a small percentage of it will decompose into its constituent elements:
When metals are near the bottom of the reactivity series, their compounds generally decompose easily at high temperatures. This is because stronger bonds form between atoms towards the top of the reactivity series, and strong bonds break less easily. For example, copper is near the bottom of the reactivity series, and copper sulfate (CuSO4), begins to decompose at about 200°C, increasing rapidly at higher temperatures to about 560°C. In contrast potassium is near the top of the reactivity series, and potassium sulfate (K2SO4) does not decompose at its melting point of about 1069°C, nor even at its boiling point.