Lattice Enthalpy and Free Energy

Question 1

Definition of second ionisation energy

Answer 1

The Enthalpy change accompanying the removal of an electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 2

How does enthalpy change of hydration vary across a period (of cations) ?

Answer 2

Charge on the cation gets larger across the period and the ions get smaller, the ionic charge is concentrated into a smaller volume so charge density increases. Attraction and bonding to water molecules will be stronger, more energy released as the hydrated ion is formed.

Question 3

Standard entropy change of reaction definition

Answer 3

The entropy change that accompanies a reaction in the molar quantities expresses in a chemical equation under standard conditions, all reactants and products being in their standard states

Question 4

Relationship between lattice enthalpy and electrostatic attraction

Answer 4

Lattice enthalpy is a measure of the strength of the electrostatic forces of attraction between the oppositely charged ions. The more energy released, so the more exothermic the lattice enthalpy, the stronger the electrostatic attraction

Question 5

Why might feasible reactions not actually occur?

Answer 5

Activation energy not been reached

Question 6

Features of lattice enthalpy

-Measuring it

Answer 6

Cannot be measured directly as it is impossible to form one mole of an ionic lattice from gaseous ions

Question 7

What are the factors which affect electrostatic attraction?

Answer 7

Ionic size

Ionic charge

Question 8

What does it mean if

a) Entropy change of reaction is positive
b) it is negative

Answer 8

a) The change has made the system more random

b) The change has made the system more ordered

Question 9

Features of lattice enthalpy

- Strength of ionic lattice

Answer 9

A large negative value for lattice enthalpy shows that there are strong electrostatic forces of attraction between the oppositely charge ions

Question 10

Entropy definition

Answer 10

S - the quantitative measure of the degree of disorder in a system

Question 11

Definition of Enthalpy change of hydration

Answer 11

The Enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions

Question 12

Units of entropy change

Answer 12

kJ mol^-1

Question 13

Definition of second electron affinity

Answer 13

The Enthalpy change that accompanies the addition of one electron to each ion in one mole of gaseous 1- ions to form one mole of gaseous 2- ions

Question 14

In what conditions do many exothermic reactions take place spontaneously?

Answer 14

At room temp.
Enthalpy content of chemical system decreases during the reaction, excess energy is released into the surroundings, increasing stability

Question 15

Definition of standard Enthalpy change of atomisation?

Answer 15

Enthalpy change which takes place when one mole of gaseous atoms is formed from its element in its standard state

Question 16

What factors are taken into account when looking at ionic size?

Answer 16

Charge and radius

Question 17

Units of enthalpy change

Answer 17

kJ mol -1

Question 18

Definition of standard Enthalpy change of solution

Answer 18

The Enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions

Question 19

What does feasible mean?

Answer 19

Consideration of enthalpy and entropy change means it is energetically possible for a reaction to take place

Question 20

Free energy change definition

Answer 20

(Delta G)
= enthalpy change - temp. x entropy change
It is the balance between the enthalpy, entropy and temperature for a process.
A process can take place spontaneously when DG is less than 0

Question 21

Requirements for an endothermic reaction to take place spontaneously

Answer 21

Entropy change must be positive and temperature must be high enough so that when multiplied by entropy change, it is greater than enthalpy change

Question 22

Definition of lattice Enthalpy

Answer 22

The Enthalpy change that accompanies the formation of 1 mole of an ionic compound from its gaseous ions under standard conditions

Question 23

How does lattice enthalpy change as the charge density on decreases?

Answer 23

As the charge density gets smaller, the electrostatic attraction between the ions decreases, lattice enthalpy becomes less exothermic

Question 24

Definition of first electron affinity

Answer 24

The Enthalpy change accompanying the addition of an electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Question 25

Definition of first ionisation energy

Answer 25

The Enthalpy change accompanying the removal of an electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 26

How does enthalpy change of hydration vary down group 1 metal ions and why?

Answer 26

The cations get larger down the group, ionic charge is spread over a larger volume and so charge density decreases. Reduced attraction to waer molecules, weaker bonds formed. Therefore, less energy would be expected to be released as the hydrated ion is formed

Question 27

What is a spontaneous process

Answer 27

A process which proceeds on its own, leading to lower energy and increased stability

Question 28

What is the relationship between the charge on the ion, the size of the ion and the charge density?

Answer 28

Charge density is directly proportional to the charge on the ion. It is inversely proportional to the size of the ion.

Question 29

How does enthalpy change of hydration vary down the group 7 halogen ions?

Answer 29

Ion gets larger so its ionic charge is spread through larger volume and electron density decreases. Less attraction to water molecules, weaker bonds formed. Therefore less energy released as hydrated ion is formed.

Question 30

Features of lattice enthalpy

- Sign

Answer 30

It is exothermic and has a negative sign because energy is given out when ionic bonds are being formed from gaseous ions

Question 31

What is the sign of S

Answer 31

Always positive as all substances possess some degree od disorder because particles are always in constant motion

Question 32

How does lattice enthalpy change as the ion increases in size?

Answer 32

Ionic charge is spread through a larger volume, hence the charge density decreases. The electrostatic attraction between the ions decreases and so the lattice enthalpy becomes less exothermic

Question 33

How does lattice enthalpy change as the size of an ion decreases?

Answer 33

The ionic charge is concentrated into a smaller volume and so charge density increases. This means the electrostatic attraction between the ions increases and so lattice enthalpy also increases