Chemistry Concepts - Atomic Mass, Moles, and Chemical Reactions

Atomic Mass and Moles

• Atomic Mass: Mass of an atom in atomic mass units (amu) relative to standard atom C (6 protons, 6 neutrons).
• Molar Mass (Atomic weight Aw): Mass of an element's atoms per mole (g/mol).

Moles

• Mole (mol): Contains $6.022 \times 10^{23}$ particles (Avogadro's number).
  • 1 mole of Al = $6.022 \times 10^{23}$ atoms.
  • 1 mole of CO₂ = $6.022 \times 10^{23}$ molecules.
• Molar Weight: Mass of 1 mole of atoms, e.g., Aw of C = 12.01 g/mol.

Molar Mass Calculations

• Molecular Weight (Mw): Sum of atomic weights in 1 mole of a molecule.
  • Example: Mw of H₂O = $2(1.008) + 16 = 18.02$ g/mol.

Percent Composition

• Calculation for ethanol (C₂H₅OH):
  • %C = $rac{(2 imes 12.01)}{46.07} \times 100 = 52.14$%
  • %H = $rac{(6 imes 1.008)}{46.07} \times 100 = 13.13$%
  • %O = $rac{(1 imes 16)}{46.07} \times 100 = 34.73$%

Chemical Reactions

• Reactants transform into products (e.g., 2HgO → 2Hg + O₂).
• Balancing Equations: Ensure equal number of atoms on both sides. E.g., C₂H₆ + 7O₂ → 4CO₂ + 6H₂O.

Stoichiometry

• Coefficients in chemical equations represent the number of moles.
• Mole ratios determine relationships between reactants/products in a chemical reaction.
  • For example, for N₂(g) + 3H₂(g) → 2NH₃(g),
  • 1 mole N₂ requires 3 moles H₂, produces 2 moles NH₃.

Problem-solving with Moles

• Example: If 85g of CH₄ consumed, $ ext{n (CH₄)} = \frac{85.0}{16.04} = 5.30$ mol CH₄ produces 5.30 mol CO₂.

Learning Checks

• Practice problems on converting grams to moles, calculating empirical and molecular formulas, and balancing equations to reinforce the concepts learned.