General Chemistry: Bookkeeping, Equilibrium, and Energy
The core toolkit
General chemistry rewards clean bookkeeping: convert every quantity to moles, then track mass, charge, and energy. Be fluent with stoichiometry and limiting-reagent logic, gas laws, solution concentration (molarity vs molality), colligative properties, and periodic trends (atomic radius, ionization energy, electronegativity, electron affinity).
Thermodynamics and equilibrium form the second cluster: ΔH, ΔS, and ΔG = ΔH − TΔS, the link ΔG° = −RT ln K, Le Châtelier shifts, and the temperature dependence of Kw. Acid–base follows: Ka, Kb, Kw, pKa, Henderson–Hasselbalch, buffer capacity, and titration landmarks (half-equivalence pH equals pKa; equivalence pH is set by the conjugate salt's behavior). Kinetics (rate laws, half-life, Arrhenius, catalysts) and electrochemistry (ΔG° = −nFE°, galvanic vs electrolytic) round it out.
Traps
- Computing pH without checking that the weak-acid approximation holds (x much smaller than [HA]).
- Claiming a catalyst changes K or ΔG - it changes only the rate.
- Letting pure solids and liquids into K, or mixing pressure and molarity units inconsistently.
- Confusing ΔG (sign depends on actual concentrations) with ΔG° (standard state only).
- Limiting-reagent problems where the obvious reagent is not limiting once you divide moles by coefficients.
Rule of thumb
For a buffer, pH = pKa + log([A⁻]/[HA]). When [A⁻] = [HA], pH = pKa, so a buffer works best within about one pH unit of its pKa.
Worked example
18 g of glucose (MW 180) is 0.10 mol. Combusted with 0.20 mol O₂ in C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, the glucose would need 0.60 mol O₂, so O₂ is limiting. CO₂ produced = 0.20 mol × (6/6) = 0.20 mol.