MATSEC IM Chemistry flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Mole definition
- The amount of substance containing the same number of elementary entities as there are atoms in exactly 12 g of carbon-12, namely 6.022 × 10²³ particles.
- Molar mass
- The mass in grams of one mole of a substance, numerically equal to its relative molecular mass or relative formula mass expressed in g mol⁻¹.
- Empirical formula
- The simplest whole-number ratio of atoms of each element in a compound, derived from percentage composition by dividing by atomic masses.
- Molecular formula
- The actual number of atoms of each element in one molecule of a compound; it is a whole-number multiple of the empirical formula.
- Limiting reagent
- The reactant that is completely consumed first in a chemical reaction, determining the maximum amount of product that can be formed.
- Avogadro constant
- The number of particles in one mole of a substance, equal to 6.022 × 10²³ mol⁻¹; used to convert between moles and number of particles.
- Molar volume of gas
- The volume occupied by one mole of any gas under specified conditions; 22.4 dm³ at STP and 24.0 dm³ at RTP.
- Concentration
- The amount of solute in moles dissolved per cubic decimetre of solution, expressed in mol dm⁻³; calculated as n/V.
- Titration equivalence point
- The point in a titration where the acid and base have reacted in the exact stoichiometric ratio; moles of H⁺ equal moles of OH⁻.
- Oxidation number
- A number assigned to an element in a compound representing the charge it would have if electrons were transferred completely; used to identify redox changes.
- Oxidation
- A process in which an atom, ion, or molecule loses electrons, resulting in an increase in its oxidation number.
- Reduction
- A process in which an atom, ion, or molecule gains electrons, resulting in a decrease in its oxidation number.
- Redox reaction
- A reaction involving simultaneous oxidation and reduction, in which electrons are transferred from a reducing agent to an oxidising agent.
- Oxidising agent
- A species that accepts electrons and is itself reduced, causing another species to be oxidised.
- Reducing agent
- A species that donates electrons and is itself oxidised, causing another species to be reduced.
- Ionic bonding
- The electrostatic attraction between oppositely charged ions formed by the complete transfer of electrons from a metal to a nonmetal.
- Covalent bonding
- A bond formed by the sharing of one or more pairs of electrons between two atoms, typically between nonmetals.
- Metallic bonding
- The electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons, explaining conductivity and malleability.
- Electronegativity
- The tendency of an atom to attract a shared pair of electrons in a covalent bond; it increases across a period and decreases down a group.
- Polar covalent bond
- A covalent bond in which the electron pair is unequally shared due to a difference in electronegativity, creating partial positive and negative charges.
- Intermolecular forces
- Weak forces of attraction between molecules, including London dispersion forces, dipole–dipole interactions, and hydrogen bonding, affecting physical properties.
- Hydrogen bonding
- A strong dipole–dipole attraction between a hydrogen atom bonded to N, O, or F and a lone pair on a nearby N, O, or F atom.
- First ionisation energy
- The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
- Atomic radius trend
- Atomic radius decreases across a period because nuclear charge increases while shielding stays similar; it increases down a group as shells are added.
- Standard enthalpy change
- The enthalpy change measured under standard conditions (100 kPa, stated temperature, usually 298 K) with all substances in their standard states.
- Exothermic reaction
- A reaction that releases heat to the surroundings, giving a negative enthalpy change (ΔH < 0) because products have lower enthalpy than reactants.
- Endothermic reaction
- A reaction that absorbs heat from the surroundings, giving a positive enthalpy change (ΔH > 0) because products have higher enthalpy than reactants.
- Bond energy calculation
- ΔH = Σ(bond energies broken) − Σ(bond energies formed); a negative result indicates an exothermic reaction.
- Hess's law
- The total enthalpy change of a reaction is independent of the route taken, provided the initial and final conditions are the same.
- Dynamic equilibrium
- The state in a reversible reaction where the forward and reverse rates are equal, so concentrations of reactants and products remain constant.
- Le Chatelier's principle
- When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, the equilibrium shifts to oppose the change.
- Brønsted–Lowry acid
- A proton (H⁺) donor; a Brønsted–Lowry base is a proton acceptor, forming a conjugate acid–base pair.