Chemical Equations (Review)

Basics of Chemical Equations

    What Are Chemical Equations?

  • Chemical equations are a way of representing chemical reactions using symbols and chemical formulas
  • They are written in the form: Reactants → Products
    • Reactants are the substances that you react together or start with
    • Products are the substances that you produce or end with

    Types of Chemical Equations

  • Word Equation: shows a reaction using the names of compounds
    • Sodium Hydroxide + Hydrochloric Acid → Sodium Chloride + Water
  • Skeleton Equation: shows an unbalanced reaction using the symbols of compounds
    • NaOH + HCl → NaCl + H2O
  • Balanced Equation: shows a balanced reaction using the symbols of compounds and coefficients
    • CH4 + 2O2 → CO2 + 2H2O

    State Symbols:

  • Used as subscripts in chemical equations to denote the physical state of substances
  • Solids are represented by (s), liquids by (l), and gases by (g)
  • A substance dissolved in water is in an aqueous state, and is represented by (aq)
  • Example (boiling water):
    • H2O(l) → H2O(g)

Balancing Chemical Equations

    How to Balance Chemical Equations

  • In balanced chemical equations, both sides should contain equal amounts of each type of element (Conservation of Mass)
  • If a chemical equation is not already balanced, coefficients need to be placed next to one or more molecules
    • Coefficients in an equation represent how many molecules of a substance will be reacted/produced in a reaction
  • Example: In H2O2 → H2O + O2, the odd number of oxygens on the right can be dealt with by multiplying H2O by 2, and then multiplying H2O2 by 2, giving 2H2O2 → 2H2O + O2

    The “MINOH” Rule

  • When balancing chemical equations, try to balance substances in the following order:
    • M - “metals” first
    • I - polyatomic “ions” second
    • N - “non-metals” third
    • O - “oxygen” fourth
    • H - “hydrogen” last

    Diatomic Elements

  • Some elements appear as diatomic molecules (pairs) in nature, which is reflected in chemical equations
  • The following "Dr HOFBrINCl" elements occur naturally as diatomic molecules:
    • H2
    • O2
    • F2
    • Br2
    • I2
    • N2
    • Cl2
  • Two other noteworthy elements are S8 and P4, which also occur naturally