How to balance a chemical reaction By Dr. Chirie Sumanasekera

1. Balance the chemical equation below: Na + Cl2 NaCl + REMEMBER…….. Cl2 = is chlorine gas. It is a diatomic molecule. Meaning, its made of two atoms covalently bonded to each other Na = is sodium metal. Nacl = sodium chloride or table salt formed by one atom of Na combining with one atom of cl. It is an binary ionic compound. (Note that the covalent bond in Cl2 is broken and atoms rearrange to form NaCl.)

1. Balance the chemical equation below: Na + Cl2 NaCl + Step 1: see how much of each atom is one either side of the equation: 2 Cl 1 Cl 1 Na 1 Na

1. Balance the chemical equation below: Na + Cl2 NaCl + Step 2: Identify which atoms (elements) are not equal on both sides of equation. And start balancing by balancing this element first: Here, Cl must be balanced! 2 Cl 1 Cl 1 Na 1 Na

1. Balance the chemical equation below: Na + Cl2 2NaCl + Step 3: Balance Cl by adding more Cl atoms to the side with less. This can be only done by changing the COEFFICIENT in front of the compound. So we place a 2 before NaCl on products side. When we do this, we have to rebalance the other side of the equation….. 2 Cl 2 Cl 1 Na 2 Na

1. Balance the chemical equation below: Na + Cl2 2NaCl 2 + Step 4: Rebalance the other side of the equation….. Need to place the coefficient of 2 before Na on reactants side. 2 Cl 2 Cl 2 x 1 Na 2 Na

1. Balance the chemical equation below: 2 Na + Cl2 2NaCl + Step5: Check if both sides of the reaction are balanced. We have 2 Na atoms and 2 Cl2 molecules (4 Cl) on the reactants side and 2 molecules of NaCl on the products side (2 Na and 2 Cl). So we have balanced this reaction! 2 Cl 2 Cl 2 Na 2 Na

2. Now Balance the reaction below: 10 Na + Cl2 NaCl 5 10 10 ___ mole Na 10 ___ mole Cl2 5 ___ mole NaCl ?

3. Now, balance the reaction below on your own: 1. Mg + Cl2 MgCl2 2. Al + Cl2 AlCl3 3. H2 + O2 H2O 4. Al + O2 Al2O3 5. CaO O2 + Ca 6. Ca(OH)2 H2O + Ca + O2

3. Check your Answers: 1. Mg + Cl2 MgCl2 2. 2Al + 3 Cl2 2AlCl3 3. 2H2 + O2 2H2O 4. 4Al + 3O2 2Al2O3 5. 2CaO O2 + 2Ca 6. 2Ca(OH)2 2H2O + 2Ca + O2