In a double replacement reaction copper (II) chloride combines with sodium nitrate. When a student combines 3 grams of copper (II) chloride react with 4 grams of sodium nitrate, how much sodium chloride is produced?
CuCl2 + 2NaNO3 --> Cu(NO3)2 + 2NaCl

To get the ∆S of the reaction, we simply have to add the ∆S of the reactants and the ∆S of the products. Then, we get the difference between the ∆S of the products and the ∆S of the products. If the ∆S is negative, then the reaction spontaneous. If the otherwise, the reaction is not spontaneous.