Grade 9 → C hemical reactions and equations ↓
Balancing Chemical Equations
Chemistry is the study of matter, its properties, and the changes it undergoes. One of the most fundamental aspects of chemistry is chemical reactions, where substances change into new substances. In a chemical reaction, reactants turn into products. These reactions are often represented using chemical equations.
What is the chemical equation?
A chemical equation is a symbolic representation of a chemical reaction. In a chemical equation, the reactants are written on the left and the products on the right, with an arrow pointing from the reactants to the products. For example, the reaction of hydrogen gas with oxygen gas to form water is written as:
2H 2 + O 2 → 2H 2 O
In this example, H 2
and O 2
are the reactants, and H 2 O
is the product.
Law of conservation of mass
In a chemical reaction, the law of conservation of mass states that mass is neither created nor destroyed. This means that the total mass of the reactants must equal the total mass of the products. For a chemical equation to satisfy this law, there must be the same number of each type of atom on both sides of the equation. This is where balancing chemical equations comes into play.
Balancing chemical equations
Balancing a chemical equation involves adjusting the coefficients (the numbers in front of chemical formulas) to make sure there are the same number of each type of atom on both sides of the equation. The coefficients represent the number of molecules, or moles, of a substance.
Steps to balance a chemical equation
- Write the unbalanced equation: Start by writing the skeletal equation with reactants and products.
- Count the atoms of each element: For each element in the equation, count the number of atoms on both sides (reactants and products).
- Adjust the coefficients: Change the coefficients to balance the atoms of each element. Never change the sub-digits in chemical formulas.
- Check your work: Make sure the number of atoms of each element is the same on both sides of the equation.
- Simplify the coefficients: If necessary, simplify the coefficients to the smallest whole numbers that balance.
Example of balancing a chemical equation
Let's look at an example to illustrate the balancing process. Consider the reaction between aluminum and oxygen that forms aluminum oxide:
Al + O 2 → Al 2 O 3
Follow the following steps:
- Write the unbalanced equation:
- Count the atoms of each element:
- Al: 1 atom on the left, 2 atoms on the right
- O: 2 atoms on the left, 3 atoms on the right
- Adjust the coefficients: To balance the aluminum, we need two aluminum atoms on the left. Then, to balance the oxygen, we adjust the coefficients.
- Al: 2 atoms on the left, 2 atoms on the right
- O: 2 atoms on the left, 3 atoms on the right
- Check your work: Verify balance:
- Al: 4 atoms on each side
- O: 6 atoms on each side
- Simplify the coefficients: In this case, the coefficients are already in their simplest whole numbers.
Al + O 2 → Al 2 O 3
2Al + O 2 → Al 2 O 3
Checking the atoms:
Note that the oxygen atoms are still unbalanced. To balance the oxygen, multiply the oxygen molecule on the left by 3/2:
2Al + (3/2)O 2 → Al 2 O 3
Alternatively, you can multiply the entire equation by 2 to remove the fraction:
4Al + 3O 2 → 2Al 2 O 3
Why is it important to keep equations balanced?
Balancing chemical equations is important because it ensures that a chemical reaction follows the law of conservation of mass. Unbalanced equations do not accurately represent the quantities of reactants and products, which can lead to incorrect calculations and misunderstandings in real-world applications such as chemical manufacturing, pharmaceuticals, and laboratory experiments.
Other examples of balancing chemical equations
Example 1: Combustion of methane
CH 4 + O 2 → CO 2 + H 2 O
Step-by-step balancing:- Write the unbalanced equation:
- Count the atoms of each element:
- C: 1 on the left, 1 on the right
- H: 4 on the left, 2 on the right
- O: 2 on the left, 3 on the right
- Adjust the coefficients: Balance the carbon and then the hydrogen:
- O: 4 on the left, 4 on the right
- Check your work: Verify balance:
- C: 1 on either side
- H: 4 on both sides
- O: 4 on both sides
CH 4 + O 2 → CO 2 + H 2 O
CH 4 + 2O 2 → CO 2 + 2H 2 O
Then check for oxygen:
Example 2: Reaction of iron with sulfur
Fe + S → FeS
Balance:- Write the unbalanced equation:
- Counting of atoms: Fe and S have the same number of atoms on both sides:
- Fe: 1 on both sides
- S: 1 on either side
- Conclusion: The equation is already balanced.
Fe + S → FeS
Visual example: equilibrium water formation
This visual illustration shows the formation of 2 molecules of water from 2 molecules of hydrogen and 1 molecule of oxygen.
Example 3: Decomposition of water
H 2 O → H 2 + O 2
Step-by-step balancing:- Write the unbalanced equation:
- Count the atoms:
- H: 2 on both sides
- O: 1 on the left, 2 on the right
- Balance the oxygen by adjusting the coefficient:
- Check your work:
- H: 4 on both sides
- O: 2 on both sides
H 2 O → H 2 + O 2
2H 2 O → 2H 2 + O 2
Tips for balancing chemical equations
- Start by balancing elements that appear in only one reactant and one product first.
- Balance polyatomic ions (if present) as a unit rather than balancing each atom separately if they appear intact on both sides.
- Place the remaining hydrogen and oxygen atoms at the end, since they are often found in multiple compounds in a reaction.
- For combustion reactions, first balance the carbon, then the hydrogen, and finally the oxygen.
- Use fractional coefficients if necessary and then multiply by the smallest integer to get whole numbers.
Common misconceptions
Here are some common misconceptions about balancing chemical equations:
- Assuming that equilibrium involves similar molecules rather than only similar atoms leads to incorrect conclusions.
- Changing the sub-numbers in a chemical formula, causing a chemical change in a substance.
- Thinking that any set of coefficients that balances one element automatically balances the equation.
Conclusion
Balancing chemical equations is an essential skill in chemistry that underlies the fundamental law of conservation of mass. Through practice and following the outlined steps and tips, balancing equations can become a systematic and straightforward process. Since chemical reactions form the backbone of many scientific investigations and industrial processes, mastering the art of balancing chemical equations ensures accuracy and integrity in chemical computations and applications.