Reaction rates. Zinc (Zn) powder being added to a solution of copper (II) sulphate (CuSO4). The rate of reaction will be fast due to the large amount of zinc exposed to the solution. The zinc is more reactive than the copper, and will replace it in the solution. Solid copper (Cu) forms on the zinc in what is termed a displacement or substitution reaction. Here, the amount of zinc exposed may exceed the (limited) amount of copper that can be substituted. A clear solution may form as the copper is used up. For a slow reaction rate and a limiting amount of zinc, see image A500/301.