Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A chemical equation is the symbolic representation of a chemical reaction using the symbols and formulae of the substances involved. For example, the reaction between magnesium and oxygen is written as .
A balanced chemical equation is one in which the number of atoms of each element is the same on both the reactant and product sides. This is based on the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction.
A skeletal chemical equation is an unbalanced representation of a reaction where the mass is not necessarily the same on both sides, such as .
To make a chemical equation more informative, physical states are mentioned: for solid, for liquid, for gas, and for aqueous (substance dissolved in water).
Specific conditions for a reaction, such as temperature, pressure, or a catalyst, are indicated above or below the arrow () in the equation.
📐Formulae
💡Examples
Problem 1:
Write and balance the chemical equation for the reaction between Hydrogen gas and Nitrogen gas to form Ammonia.
Solution:
Explanation:
Initially, the skeletal equation is . To balance the Nitrogen atoms, we add a coefficient of to . This gives Nitrogen atoms on both sides but Hydrogen atoms on the product side. To balance Hydrogen, we add a coefficient of to on the reactant side.
Problem 2:
Balance the following chemical equation: .
Solution:
Explanation:
Count the atoms of each element. There are Sodium () atoms on the product side, so we add before . This results in Hydrogen atoms and Oxygen atoms on the reactant side. To balance these, we add a coefficient of before on the product side.