Writing and Balancing Chemical Equations

Law of Conservation of Mass

• Atoms are neither created nor destroyed in chemical reactions.
• The number of atoms in reactants equals the number in products.

Structure of Chemical Equations

• Reactants: Left side of the equation.
• Products: Right side of the equation.
• Arrow: Represents 'yields' or 'produces'.

Important Elements

• Diatomic Elements: H, N, O, F, Cl, Br, I.
  • Always appear with a subscript of 2 (e.g., H₂) when alone in reactions.

Writing Chemical Equations

• Use nomenclature and charge charts for forming compounds.
  • Example: Nitrogen gas reacts with Oxygen gas to form Nitrogen Monoxide.
• State Symbols: G (gas), S (solid), L (liquid), AQ (aqueous).

Coefficients in Equations

• Represent the molar ratio of molecules involved.
• Example: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
  • 1 molecule of propane reacts with 5 of oxygen to yield 3 of carbon dioxide and 4 of water.

Balancing Equations

• Ensure equal numbers of each type of atom on both sides.
• Coefficients should be the smallest whole number ratio.
• H and O atoms are usually balanced last.

Practice Example

• Start with balancing C's, then H's, lastly O's due to their prevalence in many compounds.

Types of Chemical Reactions

• Combination Reaction: Two elements form a single product (A + B → AB).
• Decomposition Reaction: A compound breaks into elements (AB → A + B).
• Single Replacement: An element replaces another in a compound (A + BC → AC + B).
• Double Replacement: Two compounds exchange elements (AB + CD → AD + CB).
• Combustion: Hydrocarbon reacts with oxygen to produce CO₂ and H₂O.

Redox Reactions (Oxidation-Reduction)

• Involve transfer of electrons.
• Oxidation: Loss of electrons (OIL).
• Reduction: Gain of electrons (RIG).
• Example: Cu + 2AgCl → CuCl₂ + 2Ag.
  • Cu is oxidized (0 to +2), Ag is reduced (+1 to 0).

Identifying Reactions

• Recognize reaction types by the structure of reactants and products.
• Redox reactions involve changes in oxidation states.

Tips for Balancing

• Use smallest whole number ratios.
• Consider using least common multiples for coefficients.
• Systematically balance complex molecules by iterating adjustments.