1.7 Thermodynamics

Question 1

What does a negative ΔH show?

Answer 1

Exothermic Reaction

Question 2

What does positive ΔH show?

Answer 2

Endothermic Reaction

Question 3

Define lattice formation enthalpy

Answer 3

The enthalpy change when one mole of a solid ionic compound is formed from it gaseous ions.

Question 4

Define lattice dissociation enthalpy

Answer 4

The enthalpy change when one mole of a solid ionic compound is completely dissolved into its gaseous ions.

Question 5

What is special about lattice enthalpy

Answer 5

It cant be measured directly and so a number of different enthalpies have to be combined

Question 6

Enthalpy change of formation. Symbol and definition.

Answer 6

ΔHf

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states

Question 7

Bond dissociation enthalpy. Symbol and definition

Answer 7

ΔHdiss

The enthalpy change when all the bonds of the same type in 1 moles of gaseous molecules are broken

Question 8

Enthalpy change of atomisation of an element. Symbol and definition

Answer 8

ΔHat

The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state

Question 9

Enthalpy change of atomisation of a compound. Symbol and definition

Answer 9

ΔHat

The enthalpy change when 1 mole of a compound in its standard state is converted into gaseous atoms

Question 10

First ionisation energy

Answer 10

The enthalpy change when 1 mole of gaseous atoms are converted into 1 mole of gaseous 1+ ions

Question 11

First electron affinity

Answer 11

The enthalpy change when 1 mole of gaseous 1- ions are formed from one mole of gaseous atoms

Question 12

Enthalpy change of hydration

Answer 12

The enthalpy change when 1 mole of aqueous ions is formed from gaseous ions

Question 13

Enthalpy of solution

Answer 13

The enthalpy change when 1 mole of an ionic substance dissolves in enough solvent to produce an infinitely dilute solution

Question 14

How do you measure lattice enthalpy?

Answer 14

Born-Haber cycle

Question 15

What is Hess’s law?

Answer 15

The total enthalpy change of a reaction is the same no matter which route is taken

Question 16

What is the Born-Haber cycle equation?

Answer 16

Lattic Enthalpy = -Electron affinity -ionisation energy -atomisation energies + enthalpy of formation

Question 17

What do you do if you go the wrong way against an arrow in a born haber cycle?

Answer 17

Add a minus sign to the value

Question 18

How do you calculate enthalpy change of solution?

Answer 18

Lattice dissociation enthalpy + Enthalpy of hydration

Question 19

What is entropy?

Answer 19

A measure of dissorder

Question 20

Do substance like order or disorder?

Answer 20

Disorder

Question 21

What factors effect entropy and why/how?

Answer 21

Physical state - Solids have less entropy than gases as they are fixed to a point
Dissolution - Dissolving a solid increases its entropy
Number of particles - More particles means more entropy

Question 22

Equation for entropy

Answer 22

ΔS = S(products) - S(reactants)

Question 23

What must the entropy change be for most reactions to be feasible

Answer 23

Positive

Question 24

What is ΔG

Answer 24

Free energy change, a measure of how feasible a reaction is

Question 25

What does a negative or zero ΔG show?

Answer 25

The reaction is feasible

Question 26

Free energy change equation

Answer 26

ΔG = ΔH - TΔS