1. How to balance a chemical reaction
By Dr. Chirie Sumanasekera

2. 1. Balance the chemical equation below:
Na Cl 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.)

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

4. 1. Balance the chemical equation below:
Na Cl 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

5. 1. Balance the chemical equation below:
Na Cl NaCl +
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

6. 1. Balance the chemical equation below:
Na Cl NaCl 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

7. 1. Balance the chemical equation below:
2 Na Cl NaCl +
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

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

9. 3. Now, balance the reaction below on your own:
Mg Cl MgCl2
Al Cl AlCl3
H O H2O
Al O Al2O3
CaO O Ca
Ca(OH) H2O Ca O2

10. 3. Check your Answers: 1. Mg + Cl2 MgCl2 2. 2Al + 3 Cl2 2AlCl3
H O H2O
Al O Al2O3
CaO O Ca
Ca(OH) H2O Ca O2