`CuSO_4 (aq) + Mg (s) -> MgSO_4 (aq) + Cu (s)`

This is the reaction of Copper (II) sulfate solution with magnesium metal. The reaction is a single replacement reaction wherein magnesium metal replaces copper thus forming Magnesium sulfate and producing solid copper metal.

`MgSO_4 (aq) + CaCl_2 (aq) -> CaSO_4 (s)+ MgCl_2 (aq)`

This is a double replacement reaction wherein there is an exchange of species as the products are being produced. Solutions of Magnesium sulfate and Calcium chloride react to form Magnesium chloride in the solution and forming solid Calcium sulfate as precipitate.