General Chemistry Lecture Notes

Jun 26, 2024

General Chemistry Lecture Notes

Overview

  • Topics Covered: Stoichiometry, percent yield, empirical formulas, limiting reactant, conversions (grams to moles to atoms), dilution problems, balancing equations, oxidation numbers, identifying oxidizing/reducing agents, gas laws (PV=nRT), vapor pressure, partial pressure, Graham's law, mole fraction, kinetic molecular theory, solution stoichiometry, molarity, molality, Lewis structures, molecular geometry, enthalpy of reaction (bond dissociation energy, heat of formation, Hess's law), intermolecular forces, boiling point, vapor pressure, boiling point elevation, freezing point depression, osmotic pressure.

Atomic Structure and Periodic Table

  • Protons, Electrons, and Neutrons:
    • Ion: Unequal number of protons and electrons.
    • Charge = #Protons - #Electrons.
    • Atomic Number = #Protons.
    • Mass Number = Protons + Neutrons.

Naming Compounds

  • Molecular Compounds (Nonmetals):
    • Use prefixes: mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-.
    • Example: N2O5 = Dinitrogen pentoxide.
  • Ionic Compounds (Metal + Nonmetal):
    • No prefixes.
    • Example: NaCl = Sodium chloride.

Stoichiometry

  • Conversions:
    • Grams to moles: Use molar mass (g/mol).
    • Moles to atoms/molecules: Use Avogadro's number (6.022 x 10^23/mol).
    • Use balanced chemical equations to switch between moles of reactants and products.
  • Example Reaction:
    • N2 + H2 → NH3.

Solution Chemistry

  • Molarity (M): Moles of solute per liters of solution (mol/L).
  • Molality (m): Moles of solute per kilograms of solvent (mol/kg).
  • Dilution: M1V1 = M2V2.
  • Percent Composition: (mass of element/total mass) x 100%.
  • Example Calculation: Final volume needed from initial volume and molarity changes.

Oxidation-Reduction

  • Oxidation States:
    • Free elements = 0.
    • Fluorine = -1 (always when in compounds).
    • Oxygen = -2 (except peroxides = -1, with fluorine = +2).
    • Hydrogen: +1 with nonmetals, -1 with metals.
  • Balance Redox Reactions: Use half-reaction method for electrons.
  • Oxidizing and Reducing Agents: Oxidizing agent gets reduced; reducing agent gets oxidized.

Gas Laws

  • Ideal Gas Law: PV = nRT (R = 0.0821 L·atm/mol·K).
  • Graham's Law: Rate of effusion is inversely proportional to the square root of molar mass.
  • Dalton’s Law: Total pressure = sum of partial pressures.

Thermochemistry

  • Enthalpy (ΔH): Heat change at constant pressure.
  • Heat Capacity: q = mcΔT.
  • Phase Changes: Endothermic (melting, vaporization, sublimation); Exothermic (freezing, condensation, deposition).
  • Bond Dissociation Energy: Sum of energies required to break bonds.
  • Hess's Law: ΔH is the sum of ΔHs for individual steps.
  • Standard Enthalpy of Formation:
    • ΔH°f = 0 for elemental forms.
    • ΔHreaction = ΣΔH°f(products) - ΣΔH°f(reactants).

Intermolecular Forces

  • Types:
    • Hydrogen bonds (strongest, H with N, O, F).
    • Dipole-dipole interactions (between polar molecules).
    • London dispersion forces (in all molecules, dominant in non-polar).
  • Boiling Point Trends: Higher with stronger intermolecular forces.

Phase Equilibria

  • Boiling Point Elevation and Freezing Point Depression:
    • ΔTb = iKbm.
    • ΔTf = iKfm.
  • Osmotic Pressure: π = MRTi (osmotic pressure directly proportional to molarity).

Example Calculations

  1. Finding Protons, Neutrons, Electrons:
  • Example: Al³⁺ ion => 13 protons, 10 electrons, 14 neutrons.
  1. Naming Compounds:
  • Example: SO2 = Sulfur dioxide.
  1. Stoichiometry:
  • Reaction: N2 + 3H2 → 2NH3 (Calculate mass of NH3 from grams of N2).
  1. Molarity Calculation:
  • Example: M = moles/volume.
  1. Dilution Calculation:
  • Example: M1V1 = M2V2 to find water added.
  1. Oxidation State Determination:
  • Example: Chromium in Na2Cr2O7: Cr = +6.
  1. Thermochemistry:
  • Example: Calculate q using q = mcΔT.
  1. Gas Law Calculation:
  • Example: Using PV = nRT to find pressure from moles and volume.
  1. Intermolecular Forces and Boiling Points:
  • Example: CH4 (non-polar, only London dispersion forces) vs. H2O (hydrogen bonding).
  1. Osmotic Pressure Calculation:
  • Example: π = MRTi.

Final Tips

  • Understanding Concepts: Make connections between concepts (e.g., gas laws with kinetic molecular theory).
  • Practice Problems: Apply concepts to a variety of problems.
  • Use Periodic Table: For atomic masses, valence electrons, and assessing reactivity.
  • Memorize Key Equations: For quick recall during exams.