Fundamentals
The core facts every aspirant should own — each a titled nugget with a real-world story, the concept in plain words, and a memory trick. Works even when the internet doesn't.
300 fundamentals
“CO₂ has polar bonds but is non-polar; its linear shape cancels the dipoles.”
A molecule is polar only if bond dipoles don't cancel — shape matters as much as bonds.
Memory trick: Symmetry can cancel polarity.
“Squeeze a sealed syringe and the trapped air pushes back harder.”
At constant temperature, a gas's pressure is inversely proportional to its volume.
PV = constant
Memory trick: Squeeze → pressure up.
“A balloon shrinks in the freezer and swells in the sun.”
At constant pressure, a gas's volume is proportional to its absolute temperature.
V/T = constant
Memory trick: Hotter gas → bigger volume.
“Ideal-gas rules bend just when a gas is about to liquefy.”
Real gases deviate from ideal behaviour at high pressure and low temperature, where molecular size and attractions matter.
Memory trick: Ideal fails: cold + squeezed.
“Hand-warmers release heat (exothermic); instant cold-packs absorb it (endothermic).”
Heat content at constant pressure; ΔH is negative for exothermic, positive for endothermic reactions.
ΔH
Memory trick: Released → ΔH negative.
“A shuffled deck won't sort itself — disorder is the universe's default.”
A measure of molecular disorder; it tends to increase in spontaneous processes.
ΔS
Memory trick: More disorder = more entropy.
“Some endothermic reactions still happen because a big entropy gain wins.”
ΔG = ΔH − TΔS decides spontaneity; negative ΔG means spontaneous.
ΔG = ΔH − TΔS
Memory trick: ΔG < 0 → spontaneous.
“Enthalpy is like altitude — only start and end points matter, not the path.”
The total enthalpy change of a reaction is the same regardless of route.
Memory trick: ΔH is a state function.
“Equilibrium is a busy escalator that looks still — both directions run at once.”
Forward and reverse reactions occur at equal rates, so concentrations stay constant.
Memory trick: Equal rates, not equal amounts.
“Add more reactant and the reaction pushes forward to use it up.”
A disturbed equilibrium shifts to oppose the change.
Memory trick: System fights the change.
“Lemon juice (~2) is a million times more acidic than pure water (7).”
pH = −log[H⁺]; below 7 acidic, above 7 basic, 7 neutral at 25°C.
pH = −log[H⁺]
Memory trick: Each pH step = 10×.
“Stomach acid is strong; the acetic acid in vinegar is weak.”
A strong acid ionises completely (HCl); a weak acid only partly (CH₃COOH).
Memory trick: Strong = fully ionised.
“Your blood is buffered near pH 7.4 — stray far and you're in danger.”
A mix that resists pH change when small amounts of acid or base are added.
Memory trick: Weak acid + its salt.
“Adding NaCl to salty water can push extra salt out of solution.”
Adding an ion already present in an equilibrium suppresses ionisation.
Memory trick: Shared ion → less dissociation.
“A cut apple browning and iron rusting are oxidation in slow motion.”
Oxidation is loss of electrons; reduction is gain (OIL RIG).
Memory trick: OIL RIG: Oxidation Is Loss, Reduction Is Gain.
“The agent always does the opposite to itself — an oxidising agent is itself reduced.”
An oxidising agent gains electrons (is reduced); a reducing agent loses them (is oxidised).
Memory trick: Agent = opposite of its own name.
“A battery is galvanic; electroplating jewellery is electrolytic.”
A galvanic cell makes electricity from a spontaneous reaction; an electrolytic cell uses electricity to force a non-spontaneous one.
Memory trick: Galvanic gives; electrolytic needs power.
“In every cell, 'An-Ox, Red-Cat' holds true.”
Oxidation always happens at the anode; reduction at the cathode.
Memory trick: Anode = Oxidation.
“Zinc protects iron ships because zinc gives up electrons more readily than iron.”
Metals ranked by their tendency to lose electrons; reactive metals sit at the top.
Memory trick: Higher up = more reactive.
“Exactly how much metal electroplates depends on how much current you run and for how long.”
The mass deposited during electrolysis is proportional to the charge passed.
Memory trick: More charge → more metal.
“Fireworks react in a flash; rusting takes years — same chemistry, vastly different rates.”
How fast reactant is consumed or product formed per unit time.
Memory trick: Steeper concentration change = faster.
“Order is measured, not read off the balanced equation.”
The power of a reactant's concentration in the experimentally-found rate law.
Memory trick: Order comes from experiment.
“A matchstick needs a strike's energy to get the reaction over the hill.”
The minimum energy barrier reactants must cross to react.
Eₐ
Memory trick: Barrier every reaction must climb.
“Your body's enzymes are catalysts making life's reactions fast enough to live.”
Speeds a reaction by lowering activation energy, without being consumed or shifting equilibrium.
Memory trick: Lowers the hill; not used up.