Balancing Simple Chemical Equations
According to the Law of Conservation of Mass, matter can neither be created nor destroyed in a chemical reaction. Therefore, the total number of atoms of each element must be the same on both the reactant and product sides of a chemical equation.
1. The Hit and Trial Method
The most basic method for balancing simple chemical equations is the Hit and Trial method. Here, we use the smallest whole number coefficients to equalize the number of atoms.
Core Rules:
- Never change subscripts: Changing $H_2O$ to $H_2O_2$ changes the substance itself. Only change the coefficients (the numbers in front).
- Balance polyatomic ions as a whole: If $SO_4$ appears on both sides, count it as one unit to save time.
- Save Oxygen and Hydrogen for last: Usually, balancing metals and non-metals first makes the process easier.
2. Step-by-Step Example
Let's balance the combustion of Propane ($C_3H_8$):
-
Balance Carbon: There are 3 carbons on the left, so put a '3' in front of $CO_2$.
$$ C_3H_8 + O_2 \rightarrow \mathbf{3}CO_2 + H_2O $$ -
Balance Hydrogen: There are 8 hydrogens on the left, so put a '4' in front of $H_2O$ ($4 \times 2 = 8$).
$$ C_3H_8 + O_2 \rightarrow 3CO_2 + \mathbf{4}H_2O $$ -
Balance Oxygen: Count oxygens on the right: $(3 \times 2) + (4 \times 1) = 10$. To get 10 on the left, put a '5' in front of $O_2$.
$$ C_3H_8 + \mathbf{5}O_2 \rightarrow 3CO_2 + 4H_2O $$
3. Common Balancing Mistakes
Subscript Error: Writing $H_2 + O_2 \rightarrow H_2O_2$ to balance the oxygen. While mathematically "balanced," this is chemically wrong because $H_2O$ is water and $H_2O_2$ is hydrogen peroxide.
Balancing Equations Quiz
Master stoichiometry with these 10 practice questions.
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