Key Definitions Paper 1

Question 1

Alkali

Answer 1

A type of base that dissolves in water to release OH- ions.

Question 2

Covalent bonding

Answer 2

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Question 3

Electronegativity

Answer 3

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.

Question 4

d-block elements

Answer 4

Have electron configurations in which d sub-shells are their highest energy sub-shell.

Question 5

First ionisation energy

Answer 5

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.

Question 6

Standard enthalpy change of combustion

Answer 6

The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states.

Question 7

Standard enthalpy change of formation

Answer 7

The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states.

Question 8

Catalyst

Answer 8

A substance that increases the rate of a chemical reaction without being used up in the process. A catalyst provides an alternative route for the reaction with lower activation energy.

Question 9

Rate of reaction

Answer 9

The change in concentration of a reactant or product in a given time.

Question 10

The rate-determining step

Answer 10

The slowest step in the reaction mechanism of a multi-step reaction

Question 11

Buffer solution

Answer 11

A system that minimises pH changes on addition of small amounts of acid or a base.

Question 12

The standard lattice enthalpy

Answer 12

The enthalpy change that takes place when one mole of an ionic lattice is formed from its gaseous ions under standard conditions.

Question 13

The standard enthalpy change of hydration

Answer 13

The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions.

Question 14

The standard enthalpy change of solution

Answer 14

The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions.

Question 15

Entropy

Answer 15

The measure used for the dispersal of energy and disorder within the chemicals making up the chemical solution.

Question 16

The standard electrode potential

Answer 16

The e.m.f. of a half-cell compared with a standard hydrogen half-cell, measured at 298k with solution concentrations of 1 mol/dm^3 and a gas pressure of 100kPa.

Question 17

Transition element

Answer 17

A d-block element which forms an ion with an incomplete d sub-shell

Question 18

Optical isomers

Answer 18

Stereoisomers that are non-superimposable mirror images of each other.

Question 19

Bidentate ligands

Answer 19

A ligand that can donate two lone electron pairs to form two coordinate bonds to a metal ion.

Question 20

Average bond enthalpy

Answer 20

The average enthalpy change that takes place when breaking by homolytic fission one mole of a given type of bond in the molecules of a gaseous species.