Give one example of change in the substance's colour during a chemical reaction.

Change of colour in chemical reactions:

• In a chemical reaction, bonds of the reactant molecules will break and new bonds are made within the molecules of the product.
• These chemical changes are not always visible to the naked eye, but some chemical reactions are characterized by a change in the colour of reactants.
• In a chemical reaction, two or more elements combine to interact and a different structure is formed, with a different composition and colour in total.
• For example on heating, the green colour of Ferrous Sulphate (${\mathrm{FeSO}}_4$) changes to the reddish-brown colour of Ferric Oxide (${\mathrm{Fe}}_2{\mathrm{O}}_3$). $\underset{\underset{\left(\mathrm{Green}\right)}{\mathrm{Ferrous}\mathrm{Sulphate}}}{2{\mathrm{FeSO}}_4\left(\mathrm{s}\right)}\stackrel{∆}{\to }\underset{\underset{(\mathrm{Reddish}\mathrm{brown})}{\mathrm{Ferric}\mathrm{Oxide}}}{{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sulphur}\mathrm{Dioxide}}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Sulphur}\mathrm{Trioxide}}{{\mathrm{SO}}_3\left(\mathrm{g}\right)}$