Competency #7
Answer and Explanation
CH4 (g) + 2 O2 (g) 
CO2 (g) + 2 H2O (g)
To balance the equation, we must make sure there is the same number of each type of atom in the reactants as there is in the products. Rules for balancing the equation:
- We are allowed to change the coefficients.
- If no coefficient is shown, it has an implied value of ‘1’.
- Only one coefficient per molecule/compound. The coefficient tells us how many of that molecule/compound are needed or are formed in the chemical reaction. For example ‘NH3’ means there is one NH3 molecule (1 N atom and 3 H atoms), while ‘2 NH3’ means there are 2 NH3 molecules (a total of 2 N atoms and 6 H atoms).
- We are not allowed to change the subscripts while balancing the equation.
Make a table will help us to keep track of the number of each atom on each side:
CH4(g) + O2 (g) CO2 (g) + H2O (g)
| Reactants | Products | |
|---|---|---|
| 1 | C | 1 |
| 4 | H | 2 |
| 2 | O | 3 |
We can see that the above chemical equation is not balanced.
First, we might try to change the coefficient in front of the H2O from ‘1’ to ‘ 2’ in an attempt to balance the hydrogen (H) atoms. Now, we update our table:
CH4 (g) + O2 (g) CO2 (g) + 2 H2O (g)
| Reactants | Products | |
|---|---|---|
| 1 | C | 1 |
| 4 | H | 4 |
| 2 | O | 4 |
We see that the equation is still not balanced.
Next, we try to get the oxygen (O) atoms to balance by changing the coefficient in front of the O 2 from ‘1’ to ‘ 2.’ Now, we update our table:
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
| Reactants | Products | |
|---|---|---|
| 1 | C | 1 |
| 4 | H | 4 |
| 4 | O | 4 |
Now, the equation is balanced! Often, it will take some trial and error to get a balanced chemical equation.