Ch5.2 Definitions

Question 1

Define Born-Haber Cycle

Answer 1

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

Question 2

Define Conservation of Energy

Answer 2

the total energy of an isolated system remains constant (energy
cannot be lost or created).

Question 3

Define Enthalpy

Answer 3

a value that represents the heat content of a system.

Question 4

Define Enthalpy Change (ΔH)

Answer 4

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

Question 5

Define Enthalpy Change of Atomisation (ΔH)

Answer 5

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

Question 6

Define Enthalpy Change of Formation (ΔfH)

Answer 6

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

Question 7

Define Enthalpy Change of Hydration (hydH)

Answer 7

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 8

Define Enthalpy Change of Solution (solH)

Answer 8

the enthalpy change that takes place when one mole of
solute is dissolved in water

Question 9

Define First Electron Affinity

Answer 9

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 10

Define First Ionisation Energy

Answer 10

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

Question 11

Define Ionic Bond

Answer 11

electrostatic attraction between positive and negative ions.

Question 12

Define Giant Ionic Lattice

Answer 12

a regular repeating structure made up of oppositely charged ions.

Question 13

Define Lattice Enthalpy (ΔLEH)

Answer 13

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.

Question 14

Define Entropy

Answer 14

a measure of the dispersal of energy in a system. The greater the entropy, the
more disordered the system. The order of entropy for different states is solids < liquids <
gases. Increasing the number of gaseous molecules in a reaction results in an increase in
entropy.

Question 15

Define Free Energy Change (∆G)

Answer 15

the feasibility of a process depends on entropy change,
temperature and enthalpy change. The equation for Gibbs free energy is: ∆G = ∆H - T∆S. A
process is spontaneous/ feasible when ∆G is negative. Gibbs free energy doesn’t consider
kinetics.

Question 16

Define Kinetics

Answer 16

the part of chemistry relating to rates of reaction

Question 17

Define Cell Potential

Answer 17

a measure of the potential difference between two half cells, calculated by
combining 2 standard electrode potentials. The calculated cell potential can be used to
predict feasibility of a reaction, although this doesn’t consider concentration or kinetics.

Question 18

Define Electrochemical Cell

Answer 18

contains electrodes in an electrolyte and is used to generate current.
A cell could be made up of either a metal or non-metal in contact with a solution of its ions or
a solution of ions of the same element in different oxidation states with a Pt electrode. If the
cell is a standard cell, ions of the same element should have concentrations of 1 mol dm-3 or
they should be equimolar.

Question 19

E.M.F

Answer 19

electromotive force, measured in volts

Question 20

Define Equimolar Solution

Answer 20

a solution of ions in which there is an equal number of moles of each
ion.

Question 21

Define fuel cell

Answer 21

a type of cell that requires a constant supply of fuel and oxygen in order to
generate a potential difference.

Question 22

Define Redox Titration

Answer 22

a type of titration which involves the reduction of one substance and the
oxidation of another. The exact volume of titrant required to react with the analyte is
determined using an indicator which shows the end point of the reaction.

Question 23

Define Standard Electrode (Redox) Potential (Eθ
)

Answer 23

the e.m.f. of a half cell compared with a
standard hydrogen half cell. This is measured under standard conditions (1 mol dm-3 solution
concentrations, 298K and 1 atm).

Question 24

Define storage cell

Answer 24

a type of cell that can store energy. Storage cells convert chemical energy into
electrical energy by a reaction and they may be recharged by reversing the chemical
reaction.