Chemistry Content: Chemical Bonding, Reactions, and Stoichiometry
This domain tests bonding models, reaction types, equation balancing, mole conversions, limiting reactants, and yield. Expect items that combine Lewis or VSEPR reasoning with stoichiometric calculation and items that ask you to classify or predict products.
Core rules and concepts
- Ionic bonding involves electron transfer and electrostatic attraction; covalent bonding involves shared electron pairs. Electronegativity differences help classify bond polarity.
- Lewis structures track valence electrons; VSEPR predicts shape from electron-domain repulsion. Lone pairs occupy more space than bonding pairs.
- Balance equations by changing coefficients only, never subscripts. The mole ratio from a balanced equation links amounts of reactants and products.
- For limiting-reactant problems, convert each reactant to moles, divide by its coefficient, and identify the smallest quotient as limiting.
- Percent yield = (actual yield ÷ theoretical yield) × 100%.
Worked example
For 2H₂ + O₂ → 2H₂O, mix 5.0 g H₂ (molar mass 2.02 g/mol) with 10.0 g O₂ (32.00 g/mol). Moles H₂ = 2.48; moles O₂ = 0.3125. Dividing by coefficients gives 1.24 for H₂ and 0.3125 for O₂, so O₂ is limiting. O₂ produces 0.625 mol H₂O, or 11.3 g. H₂ is in excess.
Traps that cost marks
Do not use mass ratios directly from coefficients; convert to moles. Do not confuse empirical and molecular formulas. In ionic equations, cancel spectator ions. Theoretical yield comes from the limiting reactant, not the excess reactant. A balanced equation gives mole ratios, not necessarily equal masses.