General Chemistry - Stoichiometry, Equilibria and Electrochemistry
What the exam tests
General Chemistry in the Chemist Licensure Examination covers stoichiometry, gas behaviour, thermochemistry, solution equilibria, periodicity, electrochemistry and nuclear chemistry - the calculation-heavy foundation the other five domains assume.
Core rules
- Mole bridge: every quantitative problem passes through moles; convert mass with molar mass, gas volume with 22.414 L/mol at STP, and solution volume with molarity.
- Limiting reagent: divide moles by the stoichiometric coefficient; the smallest quotient limits, and percent yield = actual/theoretical × 100.
- Equilibria: Kp = Kc(RT)^Δn; weak-acid pH from Ka ≈ x²/C when x < 5 % of C; buffers follow Henderson–Hasselbalch.
- Thermodynamics: ΔG° = ΔH° − TΔS°; spontaneity requires ΔG < 0, and ΔG° = −RT ln K.
- Electrochemistry: E°cell = E°cathode − E°anode; the Nernst equation corrects for non-standard concentrations.
Worked example
Find the pH of 0.10 M acetic acid (Ka = 1.8 × 10⁻⁵). Set up Ka = x²/(0.10 − x). Assume x ≪ 0.10: x² = 1.8 × 10⁻⁶, x = 1.34 × 10⁻³ M. Check the assumption: 1.34 × 10⁻³/0.10 = 1.3 %, under 5 %, so the approximation holds. pH = −log(1.34 × 10⁻³) = 2.87.
Traps
Mixing °C and K in gas or thermodynamic formulas; forgetting Δn when converting Kp and Kc; assigning the wrong sign to work (w = −PΔV on the system); reporting pH to more figures than the data justify; using the Nernst equation with concentrations in mmol/mL instead of mol/L.