Chemical Reactions and Stoichiometry Essentials

Stoichiometry

• Area of study examining quantities of substances in chemical reactions.
• Based on the Law of Conservation of Mass.

Chemical Equations

• Represent chemical reactions on paper.
• Reactants (left) separated from products (right) by an arrow.
• "+" separates multiple reactants or products.
• States of matter: $(g) = ext{gas}$, $(l) = ext{liquid}$, $(s) = ext{solid}$, $(aq) = ext{aqueous solution.}$
• Symbols like $ext{Δ}$ over the arrow indicate heat is needed.

Balancing Equations

• Follows the Law of Conservation of Mass.
• Balance by changing coefficients, not subscripts.
• Start with elements appearing in only one reactant and product.
• Check all elements at the end.

Types of Chemical Reactions

• Combination Reactions: Two or more substances form one product.
  • Example: metal + nonmetal forming an ionic compound.
• Decomposition Reactions: One substance breaks down into two or more substances.
  • Example: metal carbonate decomposing into a metal oxide and carbon dioxide upon heating.
• Combustion Reactions: Rapid reactions producing a flame, often involving oxygen as a reactant.
  • Compounds with C and H burn to produce $CO<em>2$ and $H</em>2O$.

Formula Weight (FW)

• Sum of atomic weights for atoms in a chemical formula.
• For $H<em>2SO</em>4$: $FW = 2( ext{AW of H}) + 1( ext{AW of S}) + 4( ext{AW of O})$.

Molecular Weight (MW)

• Formula weight for a molecule.
• Sum of atomic weights of atoms in a molecule.

Percent Composition

• Percentage of mass of a compound from each element.
• \% \text{Element} = \frac{\text{(# atoms of element)} \times (\text{atomic weight})}{\text{formula weight of compound}} \times 100

Avogadro's Number and The Mole

• Mole (mol): Amount of particles in exactly $12 \text{ g}$ of C-12.
• Avogadro's Number: $6.022 \times 10^{23}$ particles per mole.

Molar Mass

• Mass of $1 \text{ mol}$ of a substance (g/mol).
• Numerically equal to formula weight (in amu).

Mole Relationships and Conversions

• Moles bridge molecular scale to real-world scale.
• Convert between mass and atoms/molecules using molar mass and Avogadro's number.

Determining Empirical and Molecular Formulas

• Empirical Formula: Simplest whole-number ratio of atoms in a compound.
  1. Convert percent composition to grams (assuming $100 \text{ g}$ sample).
  2. Convert grams to moles.
  3. Divide by the smallest number of moles to find mole ratios.
  4. If not whole numbers, multiply by suitable integer.
• Molecular Formula: Actual number of atoms in a molecule.
  • Ratio of (Molar Mass / Empirical Formula Weight) gives the whole-number multiple for the empirical formula subscripts.

Combustion Analysis

• Analyzes C, H, and O compounds by burning in oxygen.
• Mass of C determined from $CO_2$ produced.
• Mass of H determined from $H_2O$ produced.
• Mass of O determined by mass difference from original compound.

Stoichiometric Calculations

• Use coefficients in balanced equations as mole ratios to convert between amounts of different substances.
• Steps: Grams A $\rightarrow$ Moles A $\rightarrow$ Moles B $\rightarrow$ Grams B.

Limiting Reactants

• Reactant present in the smallest stoichiometric amount; consumed first.
• Determines the maximum amount of product that can be formed.
• The other reactant(s) are in excess.

Theoretical and Percent Yield

• Theoretical Yield: Maximum product calculable from stoichiometry.
• Actual Yield: Amount of product experimentally obtained.
• Percent Yield: $\% \text{Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100$