Thermodynamics/ Rate Equastion

Question 1

Bond enthalpy

Answer 1

The amount of energy required to break one mole of the stated bond in the gas phase

Question 2

Born-Haber cycle

Answer 2

Calculates the lattice enthalpy by applying Hess’s Law and comparing the standard enthalpy change of formation of the ionic compound to values such as ionisation energy and electron affinity

Question 3

Covalent character

Answer 3

The partial sharing of electrons between atoms that have an ionic bond

Question 4

Enthalpy of atomisation

Answer 4

Enthalpy change when one mole of gaseous atoms is formed from the elements in its standard states.
Always endothermic.

Na(s) —> Na(g)

Question 5

Enthalpy of formation

Answer 5

Enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions

Question 6

Enthalpy of hydration

Answer 6

Enthalpy change when one mole of a gaseous ion is completely dissolved in water under standard conditions

Na+(g) —> Na+(aq)

Question 7

Enthalpy of lattice dissociation

Answer 7

Enthalpy change when one mole of a solid ionic compound is converted into its gaseous ions

Question 8

Enthalpy of lattice formation

Answer 8

Enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions

Question 9

Enthalpy of solution

Answer 9

Enthalpy change when one mole of ionic solid completely dissolves in water under standard conditions to form an infinitely dilute solution

KCl(s) —> K+(aq) + Cl-(aq)

Question 10

Entropy

Answer 10

A measure of the disorder of a system.

The units of entropy are JK-1mol-1

On a molecular level, gases are more disordered than liquids, which are more disordered than solids.

A reaction that produces a greater number of molecules than the number of reactants molecules will have a positive entropy change, as there will exist more random arrangements of these molecules (e.g the system will become more disordered)

Question 11

Feasible reaction

Answer 11

For a reaction to be feasible at a give temperature it must occur spontaneously. This means no extra energy is required for the reaction to occur.

Question 12

First electron affinity

Answer 12

Enthalpy change when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

S(g) —> S-(g)

Question 13

First ionisation energy

Answer 13

Enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms

Question 14

Gibbs free-energy change

Answer 14

A measure of the feasibility of a chemical reaction

G = H - TS

Question 15

Ionic character

Answer 15

The amount the electrons are shared between two atoms. Limited electron sharing corresponds with a higher percentage of ionic character

Question 16

Concentration- time graph

Answer 16

A graph which can be used to deduce the rate of reaction by drawing tangents to the curve

Question 17

Order of reaction

Answer 17

Tells you how the reactants concentration will affect the rate of reaction

Question 18

Overall order of a reaction

Answer 18

Sum of all the individual orders of all the reactants in a chemical reaction

Question 19

Rate determining step

Answer 19

The slowest step in a multi- step reaction

The overall rate is decided by this step since species occurring in the RDS will also occur in the rate equation

Question 20

Rate equation

Answer 20

Describes the relationship between the rate of chemical reaction and the concentrations/ pressures of reagents