Colour change in chemical reactions

A colour change might take place when two substances react. It can also happen when a compound is broken down by heating it. This is called thermal decomposition.

Watch this video to see how the colour of copper carbonate changes when it is heated.

Thermal decomposition of copper carbonate

Copper carbonate is green and copper oxide is black. You can see a colour change from green to black during the reaction. The carbon dioxide produced can be detected using limewater, which turns cloudy.

Green copper carbonate is heated in a test tube. It changes to black copper oxide and gives off carbon dioxide gas.Copper carbonate is easily decomposed by heating