This topic explains what a chemical equation is, how to write one, and how to balance it.
Definition
The symbolic representation of a chemical reaction is called a chemical equation.
Simple explanation: A chemical equation is a shorthand way of writing what happens in a chemical reaction.
Main Idea
In a chemical equation:
- Reactants are the substances that initiate the chemical reaction.
- Products are the substances that are formed during the chemical reaction.
- Reactants are always written on the left of the equation.
- Products are always written on the right.
- An arrow between them shows the direction of the chemical change.
Simple explanation: Reactants → Products. What you start with goes on the left; what you end up with goes on the right.
Core Concept
Parts of a Chemical Equation
Reactants → Products
Example:
C(s) + O2(g) → CO2(g)
- Reactants: C and O₂
- Product: CO₂
- Arrow: shows the direction of the reaction
- State symbols: (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous
State Symbols
| Symbol | Meaning |
|---|
| (s) | Solid |
| (l) | Liquid |
| (g) | Gas |
| (aq) | Aqueous (dissolved in water) |
Detailed Explanation
Steps for Writing a Chemical Equation
For writing a chemical equation, follow these steps:
Step 1: Identify reactants and products and write a word equation for the reaction.
Reactants → Products
- s for solid
- l for liquid
- g for gas
- aq for aqueous
Simple explanation: First write the reaction in words, then replace the names with chemical formulas and add state symbols.
Example 6.11: Burning of Coal
Word equation:
Coal + Oxygen → Carbon dioxide
Chemical equation:
C(s) + O2(g) → CO2(g)
Simple explanation: Coal is carbon. When it burns in oxygen, it forms carbon dioxide.
Concept Assessment Exercise 6.6 (from the book)
Represent the following chemical reactions by chemical equations:
1. Burning of hydrogen (H₂) to produce water.
2H2(g) + O2(g) → 2H2O(l)
2. Burning of magnesium (Mg) to produce magnesium oxide (MgO).
2Mg(s) + O2(g) → 2MgO(s)
