Reaction rates. Zinc (Zn) strip standing in a solution of copper (II) sulphate (CuSO4). The rate of reaction is slow due to the small amount of zinc exposed to the solution. The zinc is more reactive than the copper, and has replaced it in the solution. Solid copper (Cu) forms on the zinc in what is termed a displacement or substitution reaction. Here, the exposed zinc becomes plated and limits the amount of copper that can be substituted. The reaction stops before the blue copper colour fades. For a fast reaction rate and a limiting amount of copper, see image A500/300.