Topic 13- Energetics II

Question 1

Define lattice energy

Answer 1

the energy change when one mole of an ionic

solid is formed from its gaseous ions

Question 2

Define enthalpy change of atomisation

Answer 2

1 mole of gaseous atoms from an element in its standard state under standard conditions

Question 3

Define electron affinity

Answer 3

the energy change when one electron is added to each atom in a one mole sample of gaseous atoms or ions.

Question 4

What does the polarisability of an anion depend on?

Answer 4

It’s radius and it’s charge

Question 5

What does the polarisability of an anion depend on?

Answer 5

It’s radius and its charge

Question 6

What does the polarising power of a cation depend on?

Answer 6

Radius and charge

Question 7

Define enthalpy change of solution

Answer 7

enthalpy change when mole of substance is dissolved in solvent under standard conditions.

Question 8

Define enthalpy change of hydration

Answer 8

The enthalpy change when one mole of gaseous ions dissolves in water to form one mole of aqueous ions under standard conditions

Question 9

What does polarisation mean?

Answer 9

positive charge from the cation attracts electrons towards it from the anion.

Question 10

lattice energy provides a measure of ….. ….. strength

Answer 10

Ionic bond strength

Question 11

Give the equation used to find entropy change of the system

Answer 11

∆S˚system =ΣS˚products - ΣS˚reactant

Question 12

In an exothermic reaction energy is given out into the surroundings. The number of ways of arranging the energy therefore…… and so the entropy of surroundings …….. and is ……..

Answer 12

number of ways arranging the energy increases and so does the entropy of surroundings and is POSITIVE

Question 13

In an endothermic reaction energy is transferred from the surroundings. The number of ways of arranging the energy in the surroundings therefore decreases and so the entropy of the surroundings ……… and is ……..

Answer 13

decreases and is negative

Question 14

Equation for total entropy change

Answer 14

Entropy change total = Entropy change system + Entropy change of surroundings

Question 15

What is entropy?

Answer 15

a measure of disorder of a system (the number of ways that particles can be arranged and the number of ways that the energy can be shared between particles

Question 16

What 3 things affect entropy

Answer 16

physical state i.e gas = high entropy
dissolving- dissolved particles can move freely
more particles=more entropy

Question 17

Substances are more energetically stable when there’s ….. disorder

Answer 17

Substances are more energetically stable when there is MORE DISORDER!

Question 18

what are the units of entropy

Answer 18

J K-1 mol-1

Question 19

how do you calculate the free energy change?

Answer 19

enthalpy change - temperature*entropy change of system

∆G = ∆H -T∆Ssystem

Question 20

What’s bond enthalpy?

Answer 20

Average enthalpy change when breaking a mole of identical bonds in the gas phase

Question 21

A reaction is more likely to happen if

Answer 21

The reaction increases the no.of moles of substance
exothermic
reaction produces gas and consumes solid

Question 22

∆G is negative then the reaction is …

Answer 22

feasible

Question 23

∆G is positive then the reaction is ….

Answer 23

not feasible

Question 24

What is the natural direction of change for entropy?

Answer 24

Increasing in total entropy (+entropy change)

Question 25

What 2 things does the theoretical lattice value assume?

Answer 25

ions are perfect spheres

charge is evenly distributed

Question 26

Why do substances want to increase their disorder?

Answer 26

So that they’re more energetically stable

Question 27

Why are some reactions feasible even when the energy change is endothermic?

Answer 27

As they are moving to try to increase their entropy (e.g. more molecules)

Question 28

When would you expect an increase in entropy when looking at an equation?

Answer 28

If the products of the forward reactions have more disorder e.g. more gas or more moles

Question 29

Why doesn’t a …… ∆G guarantee a reaction?

Answer 29

a negative ∆G doesn’t guarantee a reaction as the reaction may have a really high activation energy

Question 30

Reactions with negative ∆G, therefore feasible, have …… values for their equilibrium constants

Answer 30

negative ∆G = K GREATER than 1

value LARGE IN MAGNITUDE

Question 31

Reactions with positive ∆G, therefore not feasible, have …… values for their equilibrium constants

Answer 31

positive ∆G = K smaller than 1

value small IN MAGNITUDE

Question 32

High lattice enthalpy (large exothermic value) is due to what?

Answer 32

strong attraction between ions of HIGH CHARGE DENSITY

Question 33

Define Bond dissociation enthalpy

Answer 33

Energy required to break 1 mole of gaseous bonds to form gaseous atoms