UAE TLS Chemistry Test flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Atomic number
- The number of protons in the nucleus of an atom, which uniquely identifies the element and determines the number of electrons in a neutral atom.
- Isotopes
- Atoms of the same element with the same number of protons but different numbers of neutrons, giving different mass numbers but identical chemical properties.
- Hund's rule
- Electrons occupy degenerate orbitals singly with parallel spins before pairing up, minimising electron–electron repulsion and lowering the energy of the atom.
- Relative atomic mass
- The weighted average mass of an element's isotopes relative to one-twelfth the mass of a carbon-12 atom, calculated from isotopic masses and fractional abundances.
- Ionic bond
- An electrostatic attraction between oppositely charged ions formed when a metal transfers electrons to a non-metal, producing a giant lattice structure.
- VSEPR theory
- A model predicting molecular shape: electron domains around a central atom repel and arrange to maximise separation, with lone pairs occupying more space than bonding pairs.
- Hydrogen bonding
- A strong intermolecular attraction between a hydrogen atom bonded to N, O, or F and a lone pair on a nearby electronegative atom, raising boiling points.
- Bond order
- The number of electron pairs shared between two atoms in a bond; higher bond order corresponds to shorter, stronger bonds.
- Mole
- The amount of substance containing 6.022 × 10²³ representative particles, equal to the number of atoms in 12 grams of carbon-12.
- Limiting reagent
- The reactant that is completely consumed first in a chemical reaction, determining the maximum amount of product that can be formed.
- Molar volume
- The volume occupied by one mole of an ideal gas; at standard temperature and pressure it is approximately 22.4 dm³ mol⁻¹.
- Percentage yield
- The actual mass of product obtained divided by the theoretical maximum mass predicted by stoichiometry, multiplied by 100 to give a percentage.
- Ideal gas equation
- PV = nRT, relating pressure, volume, amount in moles, and absolute temperature, with R equal to 8.314 J mol⁻¹ K⁻¹.
- Graham's law
- The rate of effusion or diffusion of a gas is inversely proportional to the square root of its molar mass, so lighter gases escape faster.
- Vapour pressure
- The pressure exerted by vapour in equilibrium with a liquid at a given temperature; it increases with temperature and equals external pressure at boiling point.
- Boyle's law
- At constant temperature, the pressure of a fixed mass of gas is inversely proportional to its volume, so PV remains constant.
- Enthalpy change
- The heat energy exchanged with the surroundings at constant pressure; negative for exothermic reactions and positive for endothermic reactions.
- Hess's law
- The total enthalpy change of a reaction is independent of the route taken, allowing calculation of unknown enthalpy changes by summing known steps.
- Gibbs free energy
- ΔG = ΔH - TΔS; a negative value indicates a spontaneous process, while a positive value indicates the reverse is favoured.
- Calorimetry
- An experimental method measuring heat changes using q = mcΔT, where m is mass, c is specific heat capacity, and ΔT is the temperature change.
- Activation energy
- The minimum energy colliding particles must possess for a reaction to occur; it is lowered by a catalyst but unaffected by concentration.
- Le Chatelier's principle
- When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts to partially oppose that change.
- Equilibrium constant Kc
- The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric coefficient, at equilibrium at a given temperature.
- Reaction order
- The power to which a reactant's concentration is raised in the experimentally determined rate law, indicating how rate depends on that reactant.
- pH
- pH = -log[H⁺]; it measures hydrogen ion concentration, with values below 7 acidic, 7 neutral, and above 7 basic at 25 °C.
- Buffer solution
- A mixture of a weak acid and its conjugate base (or weak base and conjugate acid) that resists pH change when small amounts of acid or base are added.
- Neutralisation
- The reaction between an acid and a base producing a salt and water, with the acid and base reacting in a fixed mole ratio.
- Salt hydrolysis
- The reaction of ions from a dissolved salt with water, producing acidic or basic solutions depending on the strengths of the parent acid and base.
- Oxidation
- The loss of electrons by a species, accompanied by an increase in its oxidation number; it occurs at the anode in electrochemical cells.
- Standard electrode potential
- The potential of a half-cell measured against a standard hydrogen electrode at 1 mol dm⁻³, 1 atm, and 298 K; used to predict cell voltage.
- Electrolysis
- The use of electrical energy to drive a non-spontaneous redox reaction, with oxidation at the positive anode and reduction at the negative cathode.
- Functional group
- A specific group of atoms within a molecule that determines its characteristic chemical reactions and properties, such as -OH, -COOH, or C=C.