Definitions

Question 1

Half-life (t1/2)

Answer 1

The time taken for the concentration of a reactant to half.

Question 2

Order

Answer 2

A number that relates the rate of a reaction to the concentrations of each reactant.

Question 3

Overall Order

Answer 3

The sum of the orders with respect to each reactant.

Question 4

Rate Constant (k)

Answer 4

A constant value that relates the rate of a reaction at a given temperature to the concentrations of the reactants. For a first order reaction, this can be determined using
the relationship k = ln 2/t1/2.

Question 5

Rate-determining Step

Answer 5

The slowest step of a reaction.

Question 6

Rate equation

Answer 6

Relates rate to the concentrations of the reactants multiplied by the rate constant. Each concentration is raised to the power of the order with respect to that reactant.

Question 7

Rate of Reaction

Answer 7

A measure of how quickly a reactant is used up / a product is formed.

Question 8

Reaction Mechanism

Answer 8

A step-by-step sequence of the individual reactions that make up the overall reaction.

Question 9

Equilibrium Constant (K)

Answer 9

A value that relates the amount of products and reactants at equilibrium in a reversible reaction at a specific temperature. K is unaffected by pressure and presence of a catalyst but is affected by temperature.

Question 10

Buffer Solution

Answer 10

A system that minimises pH change on addition of small amounts of an acid or base. A buffer solution can be formed from a weak acid and a salt of the weak acid or from excess weak acid and a strong alkali.

Question 11

Carbonic Acid-Hydrogencarbonate Buffer

Answer 11

The buffer system present in blood plasma,
used to maintain blood pH between 7.35 and 7.45.

Question 12

Conjugate Acid-Base Pair

Answer 12

A pair of compounds that transform into each other by the transfer of a proton. Conjugate acid-base pairs are important in the formation of buffers to control pH.

Question 13

End Point

Answer 13

The point during a titration when the indicator changes colour. A suitable indicator should change colour near the equivalence point (it should have a pH range within the vertical section of the titration curve).

Question 14

Equivalence Point

Answer 14

The point during a titration when the amount of acid is exactly equal to the amount of base (full neutralisation occurs). When titrating an acid with a base, [H+ ] is equal to [OH− ] at this point.

Question 15

Indicator

Answer 15

A weak acid that changes colour with changing pH due to an equilibrium shift between HA and A-. For an indicator to be suitable, its pH range must be within the vertical section of the titration curve (there is no suitable indicator for weak acid-weak base titration as the titration curve does not have a vertical section)

Question 16

Born-Haber Cycle

Answer 16

A cycle which can be used to calculate the lattice enthalpy of an ionic compound using other enthalpy changes.

Question 17

Enthalpy (H)

Answer 17

A value that represents the heat content of a system.

Question 18

Enthalpy Change (ΔH)

Answer 18

The change in the heat content of a system during a reaction.

Question 19

Enthalpy Change of Atomisation (ΔH)

Answer 19

The enthalpy change that takes place when one mole of gaseous atoms is formed from an element in its standard state.

Question 20

Enthalpy Change of Formation (ΔfH)

Answer 20

The enthalpy change that takes place when one mole of a compound is formed from its elements.

Question 21

Enthalpy Change of Hydration (hydH)

Answer 21

The enthalpy change that takes place when one mole of gaseous ions are dissolved in water (exothermic). Increasing ionic charges and decreasing ionic radii make this value more negative as there would be greater attraction between the water molecules and the ions.

Question 22

Enthalpy Change of Solution (solH)

Answer 22

The enthalpy change that takes place when one mole of solute is dissolved.

Question 23

First Electron Affinity

Answer 23

The amount of energy released when one mole of electrons is added to one mole of gaseous atoms, forming one mole of 1- ions.

Question 24

First Ionisation Energy

Answer 24

The removal of one mole of electrons from one mole of gaseous atoms to form one mole of 1+ ions.

Question 25

Ionic Bond

Answer 25

Electrostatic attraction between positive and negative ions.

Question 26

Giant Ionic Lattice

Answer 26

A regular repeating structure made up of oppositely charged ions.

Question 27

Lattice Enthalpy (ΔLEH)

Answer 27

The formation of one mole of an ionic lattice from gaseous ions. Lattice enthalpy is used as a measure of the strength of ionic bonds in a giant lattice, with a more negative value meaning stronger bonds. Increasing ionic changes and decreasing ionic radii make this value more negative as there would be greater attraction between the ions.