Chapter 8 Chemical Reactions 8.2 Balancing a Chemical Equation Learning Goal Write a balanced chemical equation from the formulas of the reactants and products for a chemical reaction. © 2014 Pearson Education, Inc.

Guide to Balancing a Chemical Reaction

Learning Check Write a balanced chemical equation for the combustion of methane, CH4.

Solution Write a balanced chemical equation for the combustion of methane, CH4. Step 1 Write an equation using the correct formula of the reactants and products.

Write a balanced chemical equation for the combustion of methane, CH4. Solution Write a balanced chemical equation for the combustion of methane, CH4. Step 2 Count the atoms of each element in the reactants and products. Reactants Products 1 C atom 1 C atom Balanced 4 H atoms 2 H atoms Not balanced 2 O atoms 3 O atoms Not balanced

Solution Write a balanced chemical equation for the combustion of methane, CH4. Step 3 Use coefficients to balance each element. Since H has the most atoms, we balance the H in CH4 first by placing a 2 in front of H2O.

Write a balanced chemical equation for the combustion of methane, CH4. Solution Write a balanced chemical equation for the combustion of methane, CH4. Step 3 Use coefficients to balance each element. Recheck other atoms. Reactants Products 1 C atom 1 C atom Balanced 4 H atoms 4 H atoms Balanced 2 O atoms 3 O atoms Not balanced

Solution Write a balanced chemical equation for the combustion of methane, CH4. Step 3 Use coefficients to balance each element. We can balance O by placing a coefficient in front of O2.

Write a balanced chemical equation for the combustion of methane, CH4. Solution Write a balanced chemical equation for the combustion of methane, CH4. Step 4 Check the final equation to make sure it is balanced. Reactants Products 1 C atom 1 C atom Balanced 4 H atoms 4 H atoms Balanced 4 O atoms 4 O atoms Balanced

Solution Write a balanced chemical equation for the combustion of methane, CH4. Step 4 Check the final equation to make sure it is balanced. In a balanced reaction, the coefficients must be the lowest possible whole numbers.

Balance the following chemical equation: Learning Check Balance the following chemical equation: Na3PO4(aq) + MgCl2(aq)  Mg3(PO4)2(s) + NaCl(aq) unbalanced

Balance the following chemical equation: Solution Balance the following chemical equation: Na3PO4(aq) + MgCl2(aq)  Mg3(PO4)2(s) + NaCl(aq) Step 1 Write an equation using the correct formulas of the reactants and products.

Balance the following chemical equation: Solution Balance the following chemical equation: Na3PO4(aq) + MgCl2(aq)  Mg3(PO4)2(s) + NaCl(aq) Step 2 Count the ions of each element in the reactants and products. We compare the number of atoms in products and reactants to determine if the reaction is unbalanced.

Solution Step 2 Count the ions of each element in the reactants and products.

Step 2 Count the ions of each element in the reactants and products. Solution Na3PO4(aq) + MgCl2(aq)  Mg3(PO4)2(s) + NaCl(aq) Step 2 Count the ions of each element in the reactants and products. Reactants Products 3 Na+ 1 Na+ Not balanced 1 PO43− 2 PO43− Not balanced 1 Mg2+ 3 Mg2+ Not balanced 2 Cl− 1 Cl− Not balanced

Balance the following chemical equation: Solution Balance the following chemical equation: 2Na3PO4(aq) + 3MgCl2(aq)  Mg3(PO4)2(s) + NaCl(aq) Step 3 Use coefficients to balance each element. Reactants Products 6 Na+ 1 Na+ Not balanced 2 PO43− 2 PO43− Balanced 3 Mg2+ 3 Mg2+ Balanced 6 Cl− 1 Cl− Not balanced

Balance the following chemical equation: Solution Balance the following chemical equation: 2Na3PO4(aq) + 3MgCl2(aq)  Mg3(PO4)2(s) + 6NaCl(aq) Step 4 Check the final equation and make sure it is balanced. Add a coefficient of 6 to balance Na+, Cl−. Reactants Products 6 Na+ 6 Na+ Balanced 2 PO43− 2 PO43− Balanced 3 Mg2+ 3 Mg2+ Balanced 6 Cl− 6 Cl− Balanced