MODEL RELEASED. Chemistry experiment. Pupils performing a metal displacement reaction, which is monitored by a computer via a temperature probe (in test tube). Zinc (Zn) powder added to copper (II) nitrate (Cu(NO3)2) reacts exothermically. The aqueous solution (blue) of copper nitrate has changed colour (green, lower right) during the reaction. This occurs because solid copper is being deposited as the copper ions are replaced in the solution by zinc ions. This is known as a displacement or substitution reaction. The zinc is said to be more reactive than copper, and can be placed above it in a reactivity series.