⚖️ Equations

Mastering chemical equations and balancing

What are Chemical Equations?

Chemical equations are symbolic representations of chemical reactions. They show the reactants (starting materials) and products (ending materials) involved in a reaction, along with their relative amounts.

Main Idea: Chemical equations must be balanced to show the conservation of mass and atoms.

Parts of a Chemical Equation

Reactants → Products
General form of a chemical equation

Reactants

  • • Starting materials
  • • Left side of the arrow
  • • Substances that react
  • • Separated by + signs

Products

  • • Ending materials
  • • Right side of the arrow
  • • Substances formed
  • • Separated by + signs

Example: Hydrogen + Oxygen → Water

H₂ + O₂ → H₂O
H₂
Hydrogen gas
O₂
Oxygen gas
H₂O
Water

Note: This equation is not balanced yet. We need to add coefficients to balance it.

Balancing Chemical Equations

Balancing equations ensures that the same number of each type of atom appears on both sides of the equation, following the Law of Conservation of Mass.

Steps to Balance Equations:

Step 1: Write the Unbalanced Equation

H₂ + O₂ → H₂O

Step 2: Count Atoms on Each Side

Reactants:
H: 2 atoms
O: 2 atoms
Products:
H: 2 atoms
O: 1 atom

Step 3: Add Coefficients to Balance

2H₂ + O₂ → 2H₂O
Now we have 4 H atoms and 2 O atoms on both sides!

Types of Chemical Reactions

Synthesis (Combination)

Two or more substances combine to form a single product.

A + B → AB
Example: 2H₂ + O₂ → 2H₂O

Decomposition

A single compound breaks down into two or more simpler substances.

AB → A + B
Example: 2H₂O₂ → 2H₂O + O₂

Single Replacement

One element replaces another in a compound.

A + BC → AC + B
Example: Fe + CuSO₄ → FeSO₄ + Cu

Double Replacement

Two compounds exchange ions to form new compounds.

AB + CD → AD + CB
Example: AgNO₃ + NaCl → AgCl + NaNO₃

State Symbols

State symbols indicate the physical state of each substance in the reaction.

(s)
Solid
(l)
Liquid
(g)
Gas
(aq)
Aqueous (dissolved in water)

Example with State Symbols:

2H₂(g) + O₂(g) → 2H₂O(l)

Hydrogen gas and oxygen gas react to form liquid water.

Coefficients vs Subscripts

Coefficients

  • • Numbers in front of formulas
  • • Apply to entire molecule
  • • Can be changed to balance
  • • Example: 2H₂O means 2 water molecules
2H₂O = 4 H atoms + 2 O atoms

Subscripts

  • • Numbers after element symbols
  • • Part of the chemical formula
  • • Cannot be changed
  • • Example: H₂O means 2 H atoms per molecule
H₂O = 2 H atoms + 1 O atom

Practice Examples

Example 1: Carbon + Oxygen → Carbon Dioxide

C + O₂ → CO₂

This equation is already balanced! 1 C and 2 O atoms on both sides.

Example 2: Nitrogen + Hydrogen → Ammonia

N₂ + H₂ → NH₃
N₂ + 3H₂ → 2NH₃

Balanced: 2 N atoms and 6 H atoms on both sides.

Lazy Read

  • • Chemical equations show reactants → products
  • • Equations must be balanced (same atoms on both sides)
  • • Coefficients multiply entire molecules, subscripts are part of formulas
  • • State symbols show physical states: (s), (l), (g), (aq)
  • • Four main reaction types: synthesis, decomposition, single replacement, double replacement
  • • Balancing follows the Law of Conservation of Mass
  • • Start with elements that appear in only one reactant and one product
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