Chemistry II: Kinetics, Equilibrium, Electrochemistry, and Biological Buffers

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Rate law: rate = k[A]ᵐ[B]ⁿ, with orders found experimentally.
Integrated rate laws: first order ln[A] = ln[A]₀ − kt, with half-life t½ = ln 2/k; zero order [A] = [A]₀ − kt; second order 1/[A] = 1/[A]₀ + kt.
Collision theory and the Arrhenius equation k = Ae^(−Eₐ/RT); a plot of ln k against 1/T has gradient −Eₐ/R.
Catalysts lower the activation energy. Enzymes are biological catalysts; drug metabolism often follows first-order kinetics, so half-life matters in dosing.
Example: a first-order reaction with k = 0.0231 min⁻¹ has t½ = 0.693/0.0231 = 30.0 min; after 60 min, one quarter remains.

Equilibrium constants: Kc, Kp = Kc(RT)^Δn; compare Q with K to predict direction. Le Chatelier's principle.
Acids and bases: Brønsted-Lowry theory; Kw = 1.0 × 10⁻¹⁴ at 25 °C; pH = −log[H⁺]; Ka, Kb, pKa; strong and weak acids; titration curves and indicators.
Buffers: pH = pKa + log([A⁻]/[HA]) (Henderson-Hasselbalch). A buffer resists pH change.
Biological buffers: the bicarbonate buffer system (H₂CO₃/HCO₃⁻) is the main buffer of blood plasma, which is kept at pH 7.35 to 7.45. Proteins (including haemoglobin) and phosphate also buffer. Departures from this range cause acidosis or alkalosis, which are medical emergencies. The respiratory system (removing CO₂) and the kidneys (excreting H⁺ and regenerating bicarbonate) help maintain pH.
Solubility equilibria: Ksp, the common-ion effect; kidney stones (calcium oxalate and phosphate) and dental enamel (hydroxyapatite) are practical examples.
Distribution law and solvent extraction; phase equilibria and Raoult's law (in some versions).
Osmosis and colligative properties: osmotic pressure Π = cRT, relevant for intravenous fluids (isotonic saline is about 0.9 percent NaCl).

Galvanic cells: E°cell = E°cathode − E°anode; ΔG° = −nFE°; the Nernst equation E = E° − (RT/nF) ln Q (about E° − (0.0592/n) log Q at 25 °C).
Electrolysis and Faraday's law m = MIt/(nF).
Biological relevance: nerve impulses and membrane potentials depend on ion gradients across membranes, described by the same principles; the pH electrode and the ECG rely on electrochemical principles. Batteries, corrosion, and fuel cells are applications.

CHAPTER 17