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Understanding Chemistry and Stoichiometry

Mar 13, 2025

Chemistry Lecture Notes

Key Concepts

  • Chemistry explains the visible world by describing the invisible particles.
  • Chemistry deals with infinitesimal particles, which are the building blocks of mass.
  • Stoichiometry is the science of measuring chemicals in reactions, allowing us to count atoms and molecules by weighing them.

Measurement in Chemistry

  • Relative Atomic Mass: A weighted average of the masses of all naturally occurring isotopes of an element.
    • Example: Carbon has isotopes C-12, C-13, C-14.
    • The relative atomic mass of carbon is 12.01 amu.

Atomic Mass Units (amu)

  • 1 amu is defined as 1/12th of the mass of a carbon-12 atom.
  • History of atomic weight measurement:
    • Initially measured using hydrogen.
    • Shifted to oxygen in the mid-1800s.
    • Finally standardized to carbon-12 in 1961.

Moles and Avogadro's Number

  • Mole: Allows expression of atomic mass in grams.
    • Defined using carbon-12: 6.022 x 10^23 atoms of carbon-12 = 12 grams.
    • Avogadro's Number: 6.022 x 10^23, the number of atoms or molecules per mole.
  • Molar Mass: Mass of one mole of a substance, equivalent to its atomic mass in grams.

Calculating Molar Mass

  • Add up the molar masses of a compound's components.
    • Example: Sucrose (C12H22O11)
      • Contains 12 moles of carbon, 22 moles of hydrogen, and 11 moles of oxygen.

Chemical Reactions and Stoichiometry

  • Equations must balance the number of atoms of each element on both sides (law of conservation of mass).
  • Equation Balancing: Ensures reactants and products contain the same number of atoms.
    • Example: Metabolizing sucrose with oxygen creates CO2 and water.

Practical Stoichiometry

  • Convert balanced equations from molecules to moles and then to grams.
    • Ratio: 384 grams of oxygen for every 342.3 grams of sucrose.
    • Example Calculation: To burn 5 grams of sugar requires 5.6 grams of oxygen.

Summary

  • Important units: Atomic mass units and moles.
  • Calculation methods for molar mass and reaction balancing.
  • Using molar ratios to calculate reactant and product amounts in reactions.

Credits: Lecture by Crash Course Chemistry team.

  • Filmed, edited, and directed by Nick Jenkins.
  • Written by Blake de Pastino, edited by Dr. Heiko Langner.
  • Sound design by Michael Aranda.
  • Graphics by Thought Cafe.

Full transcript