Overview of Stoichiometry and Reactions

Sep 23, 2024

Chem 1210 Lecture Notes

Exam Update

  • Exam results will be available by the end of Friday.

Stoichiometry Review

  • Mole Concept: Serves as the interchange between macroscopic and atomic scales.
    • Conversion Factors:
      • Molar mass (grams/mole)
      • Avogadro’s number (particles/mole)

Analysis Techniques

  • Mass percentage to empirical formula.
  • Combustion Analysis:
    • Complete combustion: Fuel + O2 → CO2 + H2O
    • Determine the empirical formula of fuel by measuring CO2 and H2O masses.

Example Problem: Combustion of Hydrocarbon

  • Given: 299.4g CO2, 163.4g H2O
  • Steps:
    1. Convert grams of CO2 to moles using molar mass.
    2. Use chemical formula to find moles of carbon.
    3. Repeat for H2O to find moles of hydrogen.
    4. Calculate mole ratio to find empirical formula: C3H8.

Combustion of Menthol Example

  • Steps:
    1. Calculate mass of carbon and hydrogen.
    2. If excess mass exists, attribute to oxygen.
    3. Convert all elements to moles and determine ratios.
    4. Empirical formula example: C10H20O.

Balanced Chemical Equations

  • Provide relative number of moles between substances.
  • Stoichiometric equivalence: Moles of reactants/products are related by coefficients.
  • Example: 2H2 + O2 → 2H2O

Stoichiometric Calculations

  • Example: How many moles of H2O from 0.34 moles O2?

    • Use balanced equation for conversions.
    • Result: 0.68 moles of H2O produced.

  • Grams to Grams Example:

    • Convert mass of O2 to moles, use stoichiometry, convert to grams of H2O.
    • Example calculation results in 11.5g H2O from 10.2g O2.

Limiting Reactants

  • Limiting reactant limits reaction progress.
  • Reaction stops when limiting reactant is consumed.

Example: Ammonia Synthesis

  • Use given moles of reactants to determine limiting reactant.
  • Calculate product yield based on limiting reactant.
  • Example: N2 + 3H2 → 2NH3

Percent Yield

  • Theoretical Yield: Max possible product from limiting reactant.
  • Actual Yield: Product actually obtained.
  • Percent Yield: (Actual/Theoretical) x 100%
    • Indicative of reaction efficiency.

Example Problem

  • Purification of iron from iron ore.
  • Use balanced equation to determine theoretical yield.
  • Given actual yield, calculate percent yield.
    • Example: 71.6% yield indicates efficiency.

Closing

  • Work on homework problems.
  • Next topic: Chemical reactions in aqueous solutions.

These notes provide a comprehensive overview of stoichiometry, combustion analysis, stoichiometric calculations, limiting reactants, and yield calculations in chemistry. They include theoretical explanations, step-by-step problem-solving methods, and example problems to illustrate key concepts.