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
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
A frequent error is thinking k depends on concentration. In reality, the proportionality constant k in the rate law; it rises sharply with temperature.
Memory trick: k depends on temperature and catalyst, not on how much reactant you have.
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
A frequent error is thinking a catalyst changes ΔH or the position of equilibrium. In reality, the minimum energy barrier reactants must cross; a catalyst lowers it.
Memory trick: a catalyst speeds BOTH directions equally — it never shifts equilibrium.
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
The time for a reactant to fall to half its amount; for first-order reactions it's constant.
Memory trick: constant half-life is a signature of first-order kinetics.
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
A frequent error is assuming half-life is constant for every order. In reality, the time for a reactant to fall to half its amount; for first-order reactions it's constant.
Memory trick: constant half-life is a signature of first-order kinetics.
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
Arrhenius equation linking rate constant to temperature. Use it when Ea is the activation energy.
k = A·e^(−Ea/RT)
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
Half-life of a first-order reaction. Use it when first-order kinetics only.
t½ = 0.693/k
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
Order is experimental and can be zero or fractional; molecularity is the count of species in an elementary step and is always a whole number.
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
Rate depends on concentration and changes as the reaction proceeds; the rate constant k is fixed at a given temperature.
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
A catalyst speeds a reaction by lowering activation energy but does NOT shift the equilibrium position.
“Food lasts longer in a fridge because cold slows the reactions that spoil it.”
Order is found by experiment; it only matches the coefficients for a genuinely elementary reaction.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A galvanic cell turns a spontaneous reaction into electricity; an electrolytic cell uses electricity to drive a non-spontaneous reaction.
Memory trick: galvanic = battery (gives energy); electrolytic = needs a power source.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A frequent error is swapping which cell is spontaneous. In reality, a galvanic cell turns a spontaneous reaction into electricity; an electrolytic cell uses electricity to drive a non-spontaneous reaction.
Memory trick: galvanic = battery (gives energy); electrolytic = needs a power source.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A frequent error is assuming the anode is always the positive terminal. In reality, oxidation always happens at the anode and reduction always at the cathode.
Memory trick: 'An-Ox, Red-Cat' — Anode Oxidation, Reduction Cathode, in every cell.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
The tendency of an electrode to gain electrons; cell EMF = E(cathode) − E(anode).
Memory trick: a positive cell EMF means the reaction is spontaneous.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A frequent error is forgetting to keep reduction potentials consistent when subtracting. In reality, the tendency of an electrode to gain electrons; cell EMF = E(cathode) − E(anode).
Memory trick: a positive cell EMF means the reaction is spontaneous.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A frequent error is using standard potentials when concentrations aren't 1 M. In reality, adjusts electrode potential for non-standard concentrations.
Memory trick: ΔG = −nFE links free energy to cell voltage.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
Standard cell EMF from electrode potentials. Use it when standard conditions.
E_cell = E_cathode − E_anode
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
Free energy change from cell potential. Use it when n = electrons transferred, F = Faraday constant.
ΔG = −nFE
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A galvanic cell produces electricity from a spontaneous reaction; an electrolytic cell consumes electricity to force a non-spontaneous one.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
Oxidation occurs at the anode and reduction at the cathode — in every cell, regardless of the terminal signs.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
The anode is negative in a galvanic cell but positive in an electrolytic cell; only 'oxidation at the anode' is always true.
“Every medicine, plastic and fuel is a story written in carbon.”
A permanent shift of electron density through sigma bonds due to electronegativity differences.
Memory trick: it weakens rapidly with distance — mostly the nearby atoms feel it.
“Every medicine, plastic and fuel is a story written in carbon.”
A frequent error is thinking the inductive effect travels undiminished along a chain. In reality, a permanent shift of electron density through sigma bonds due to electronegativity differences.
Memory trick: it weakens rapidly with distance — mostly the nearby atoms feel it.
“Every medicine, plastic and fuel is a story written in carbon.”
A frequent error is believing the separate resonance structures actually exist and interconvert. In reality, delocalisation of electrons over several atoms, giving extra stability.
Memory trick: the real molecule is a single averaged hybrid of all structures.