U4 Section #1

Coefficients and Subscripts

• Coefficients

  • Numbers placed before compounds to indicate how many molecules are present.

  • Example: In the equation 2H₂ + O₂ → 2H₂O, the coefficient "2" indicates there are 2 molecules of diatomic hydrogen (H₂) and 2 molecules of water (H₂O).

• Subscripts

  • Numbers written after an element symbol to indicate the number of atoms of that element in a molecule.

  • Example: In H₂O, the subscript "2" indicates there are 2 hydrogen atoms.

Examples

• Chemical Reactions

  • Reaction: 2H₂ + O₂ → 2H₂O

    • Reactants:

      • 2H₂ (2 Hydrogen molecules) + O₂ (1 Oxygen molecule)

    • Products:

      • 2H₂O (2 Water molecules)

• Water (H₂O)

  • Composition:

    • 2 Hydrogen atoms and 1 Oxygen atom in one molecule of water.

  • Example Representation:

    • 2H₂O indicates 2 molecules of water, which equates to 4 H atoms and 2 O atoms.

• Hydrogen Peroxide (H₂O₂)

  • Composition:

    • 2 Hydrogen atoms and 2 Oxygen atoms in one molecule.

  • Examples of Atoms Counted:

    • 2 H atoms and 2 O atoms represent a total of 4 H atoms and 2 O atoms in the compound.