Chemical Reactions and Equations

General Features of Physical and Chemical Changes

  • Physical change: Alters physical state without changing composition.
  • Chemical change (reaction): Converts one substance into another, involving breaking bonds in reactants and forming new bonds in products.

Writing Chemical Equations

  • Chemical equation: Uses formulas and symbols to show reactants and products.
    • Reactants: Written on the left.
    • Products: Written on the right.
    • Coefficients: Show the number of molecules reacting or formed.
  • Law of conservation of mass: Atoms are neither created nor destroyed.
  • Balanced equation: Same number of atoms of each element on both sides, achieved using coefficients.

Symbols Used in Chemical Equations

  • \rightarrow : Reaction arrow.
  • \Delta : Heat.
  • (s): Solid.
  • (l): Liquid.
  • (g): Gas.
  • (aq): Aqueous solution.

Balancing Chemical Equations

  • Balance equations by adjusting coefficients, not subscripts.
  • Balance one element at a time.
  • Ensure the smallest whole number coefficients are used.

Types of Reactions

  • Combination: Two or more reactants form a single product (A + B → AB).
  • Decomposition: Single reactant converts to two or more products (CD → C + D).
  • Single replacement: One element replaces another in a compound (A + CD → C + AD).
  • Double replacement: Two compounds exchange parts (CD + EF → CF + ED).

The Mole and Avogadro’s Number

  • Mole: Quantity containing 6.02 \times 10^{23} items (Avogadro's number).
  • Conversion factor: Relates moles to the number of atoms or molecules.

Mass to Mole Conversions

  • Formula weight: Sum of atomic weights in atomic mass units (amu).
  • Molar mass: Mass of one mole in grams per mole (g/mol); numerically equal to formula weight in amu.
  • Conversion factor: Molar mass relates grams to moles.

Mole Calculations in Chemical Equations

  • Balanced equations indicate mole ratios between reactants and products.
  • Mole ratios: Used as conversion factors.

Mass Calculations in Chemical Equations

  • Convert moles of reactant to moles of product using mole ratios.
  • Convert moles of product to grams using molar mass.

Percent Yield

  • Theoretical yield: Expected product amount from a given reactant amount.
  • Actual yield: Amount of product isolated from a reaction.
  • Percent yield: (\frac{Actual Yield}{Theoretical Yield}) \times 100