Understanding Chemical Equations and Balancing

Chemical Equation

  • Definition: A chemical equation is a symbolic representation of a chemical reaction using chemical formulas.

  • Components:

    • Reactant (SM): The starting material, or substance undergoing change in a chemical reaction.

    • Product (P): The substance that results from the reaction.

  • Common States of Matter for SM and P:

    • (g): Gas

    • (l): Liquid

    • (s): Solid

    • (aq): Aqueous solution (a solution in water)

  • Symbols Used in Equations:

    • ­: Indicates gas evolution during the course of the reaction.

    • ¯: Indicates precipitation of solid from solution.

  • Catalyst: A substance that speeds up the reaction without undergoing any overall change itself during the reaction.

  • Reaction Conditions:

    • Specific: Conditions like temperature, pressure, solvent, and reaction time.

    • General:

    • D: Heat

    • hn: Light

    • Electrical current: Represented as a symbol in the equation.

Coefficients and Balancing

  • Coefficient Definition: A coefficient is a number placed before a substance's formula in a chemical equation.

  • Purpose: It indicates the relative mole amount of each reactant and product involved.

  • Balancing Equations:

    • A balanced equation is one where the number of all atoms on both sides of the equation is equal for each element.

  • Preferred Coefficients: Use the smallest possible whole numbers.

  • Balancing Methods:

    • Inspection (Trial-and-Error): Start with atoms that are represented in only one substance on each side, if possible.

    • Half-Reactions: This method works particularly well for complex redox (reduction-oxidation) reactions.

  • Examples of Balancing:

    • Example 1:

    • ext{Fe}2 ext{O}3 (s) + ext{CO} (g)
      ightarrow ext{Fe} (s) + ext{CO}_2 (g)

    • Example 2:

    • ext{CH}4 + ext{O}2
      ightarrow ext{CO}2 + ext{H}2 ext{O}

    • Example 3:

    • ext{Fe} + ext{H}2 ext{SO}4
      ightarrow ext{Fe}2( ext{SO}4)3 + ext{H}2 ext{ } ¯

    • Example 4:

    • ext{AgNO}3 + ext{AlBr}3
      ightarrow ext{Al}( ext{NO}3)3 + ext{AgBr} ¯