A chemical reaction occurs when the reactants break into constituent ions and recombine to form different products. In this case, lead nitrate and potassium chromate recombine to form lead chromate and potassium nitrate. For the equation of the reaction to be balanced, the number of atoms on each side of the equation must match.
- Write the unbalanced equation
Put the reactants on the left-hand side of the equation and the products on the right-hand side: Pb(NO3)2 + K2CrO4 = PbCrO4 + KNO3. This equation shows the recombination of ions that can be expected to occur after they dissociate in solution, but it is not yet balanced. Traditionally, an arrow is used instead of an equal sign to show the direction the reaction tends to follow.
- Write an inventory of the atoms
Make one list for reactants and one for products. In this case, the reactants are Pb = 1, NO3 = 2, K = 2 and CrO4 = 1. The products are Pb = 1, NO3 = 1, K = 1 and CrO4 = 1. The inventory shows that quantities of Pb and CrO4 are balanced on both sides of the equation, but the quantities for K and NO3 are not.
- Find the coefficients that balance the inventory
Place a coefficient of 2 in front of KNO3 to correct the imbalances for both the K and NO3 ions. The final balanced equation is Pb(NO3)2 + K2CrO4 = PbCrO4 + 2KNO3.