Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A Balanced Chemical Equation is a representation where the number of atoms of each element on the reactant side is equal to the number of atoms on the product side.
The balancing of chemical equations is based on the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction. Hence, the total mass of elements present in the products must be equal to the total mass of elements present in the reactants.
To balance an equation, we use the Hit and Trial Method, where we multiply the chemical formulae by the smallest possible whole number coefficients.
During balancing, the chemical formulae of the substances (subscripts) must never be changed; only the coefficients (numbers in front of the formulae) can be adjusted.
Physical states are often mentioned for completeness: for solid, for liquid, for gas, and for aqueous (dissolved in water).
Essential conditions such as temperature, pressure, or a catalyst are written above or below the reaction arrow ().
📐Formulae
💡Examples
Problem 1:
Balance the following chemical equation:
Solution:
Explanation:
First, balance the element with the maximum number of atoms, which is Oxygen. There are 4 Oxygen atoms in , so we put coefficient 4 before on the LHS. Now, there are 8 Hydrogen atoms on the LHS, so we put coefficient 4 before on the RHS. Finally, there are 3 Iron atoms on the RHS, so we put coefficient 3 before on the LHS.
Problem 2:
Write the balanced chemical equation for: Sodium hydroxide solution reacts with hydrochloric acid solution to produce sodium chloride solution and water.
Solution:
Explanation:
Counting the atoms: : 1 (LHS), 1 (RHS); : 1 (LHS), 1 (RHS); : 2 (LHS), 2 (RHS); : 1 (LHS), 1 (RHS). Since the number of atoms for every element is already equal, the equation is already balanced.
Problem 3:
Balance the reaction between Aluminium and Copper chloride:
Solution:
Explanation:
Start with Chlorine (). It has 2 atoms on the LHS and 3 on the RHS. To balance, find the LCM (6). Multiply by 3 and by 2. Now balance Aluminium () by adding 2 on the LHS and Copper () by adding 3 on the RHS.