NEB Class 12 Chemistry flashcards
NEB Class 12 Chemistry · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Rate law
- An experimentally determined equation expressing reaction rate as rate = k[A]^m[B]^n, where m and n are the order with respect to each reactant and are not necessarily the stoichiometric coefficients.
- Half-life (first order)
- The time for half the reactant to be consumed; for a first-order reaction t½ = 0.693/k, independent of initial concentration, making it a useful diagnostic for first-order kinetics.
- Arrhenius equation
- k = A·e^(−Ea/RT), relating the rate constant to activation energy Ea and temperature T. A higher Ea makes k more sensitive to temperature change.
- Hess's law
- The enthalpy change of a reaction is the same regardless of the route taken, allowing ΔH to be calculated by summing known enthalpies of formation, combustion, or bond energies.
- Gibbs free energy
- ΔG = ΔH − TΔS. A negative ΔG indicates a spontaneous process at constant temperature and pressure; ΔG = 0 at equilibrium.
- Le Chatelier's principle
- When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts in the direction that partially opposes the change.
- Colligative properties
- Properties depending on the number of solute particles, not their identity: relative lowering of vapour pressure, boiling point elevation, freezing point depression, and osmotic pressure.
- Nernst equation
- E = E° − (0.059/n)·log Q at 298 K, giving the cell potential under non-standard conditions; at equilibrium, E = 0 and E° = (0.059/n)·log K.
- Effective nuclear charge
- The net positive charge experienced by an outer electron after subtracting shielding by inner electrons; it explains periodic trends in atomic radius and ionisation energy.
- Diagonal relationship
- Similarity in chemical properties between certain elements in diagonal positions of the periodic table, such as Li–Mg and Be–Al, arising from similar charge-to-radius ratios.
- Hydrogen bonding in HF
- Strong hydrogen bonding in HF makes it a weak acid compared with HCl, because the H–F bond and solvation are less favourable for releasing a proton.
- Transition metal colour
- Colour arises from d–d electronic transitions when partially filled d orbitals split unevenly in a ligand field; ions with d⁰ or d¹⁰ configurations are usually colourless.
- IUPAC ligand naming
- Ligands are named alphabetically before the metal, with prefixes di-, tri-, bis-, and tris-; anionic ligands end in -o, and the metal oxidation state is in Roman numerals.
- Amphoteric oxide
- An oxide that reacts with both acids and bases to form salts, such as Al₂O₃ and ZnO; it is typical of elements with intermediate electronegativity.
- Paramagnetism
- Attraction into a magnetic field caused by unpaired electrons; in transition metal ions it increases with the number of unpaired d electrons.
- EAN rule
- The effective atomic number rule states that stable complexes often have a central metal with the electron count of the next noble gas, commonly 18 electrons.
- Markovnikov's rule
- In addition of HX to an unsymmetrical alkene, the hydrogen adds to the carbon with more hydrogens, giving the more stable carbocation intermediate and the major product.
- SN1 versus SN2
- SN1 is a two-step, carbocation pathway favoured by tertiary substrates and polar protic solvents; SN2 is a one-step, backside attack favoured by primary substrates and polar aprotic solvents.
- Hückel's rule
- A cyclic, planar, fully conjugated system is aromatic if it has 4n+2 π electrons; 4n π electrons in the same geometry give antiaromatic character.
- Tollens' test
- Ammoniacal silver nitrate oxidises aldehydes to carboxylate and deposits a silver mirror; ketones give no reaction, distinguishing the two carbonyl types.
- Lucas test
- Anhydrous ZnCl₂ in concentrated HCl gives immediate turbidity with tertiary alcohols, slow turbidity with secondary, and no reaction with primary alcohols at room temperature.
- Saytzeff's rule
- In elimination, the more highly substituted alkene is the major product because it is more stable, arising from the more stable transition state.
- Carboxylic acid derivatives
- Reactivity order toward nucleophilic acyl substitution: acid chloride > anhydride > ester > amide, determined by the leaving group ability and electron donation.
- Amine basicity
- Amines are basic due to the lone pair on nitrogen; in water, secondary amines are often most basic because inductive and solvation effects combine favourably.
- Henderson–Hasselbalch equation
- pH = pKa + log([salt]/[acid]), used to calculate the pH of a buffer; maximum buffer capacity occurs when pH equals pKa.
- Solubility product
- Ksp is the equilibrium constant for a sparingly soluble salt; precipitation occurs when the ionic product exceeds Ksp, and a common ion lowers solubility.
- Beer–Lambert law
- A = εbc, where absorbance is proportional to concentration and path length; it is the basis of colorimetric determination using a calibration curve.
- Rf value
- In chromatography, Rf is the distance travelled by the solute divided by the distance travelled by the solvent front; it is characteristic of a compound under fixed conditions.
- Flame test colours
- Characteristic flame colours identify metal ions: sodium golden yellow, potassium lilac, calcium brick red, barium apple green, and copper blue-green.
- BOD versus COD
- BOD measures oxygen consumed by microorganisms degrading organic matter, while COD measures total oxidisable matter by a strong chemical oxidant; COD is generally higher.
- Gravimetric factor
- The ratio of the molar mass of the sought substance to that of the weighed precipitate, multiplied by the precipitate mass to obtain the analyte mass.
- Acid rain
- Rain with pH below about 5.6, caused mainly by SO₂ and NOx emissions forming sulphuric and nitric acids, which damage buildings, soils, and aquatic life.