Thermodynamics

Question 1

What is lattice enthalpy?

Answer 1

A measure of the strength of the forces between the ions in an ionic lattice

Question 2

What attractions form between positive and negative ions?

Answer 2

Electrostatic attractions

Question 3

How are electrostatic attractions and lattice enthalpy linked?

Answer 3

The stronger the electrostatic attractions the greater the lattice enthalpy

Question 4

What is lattice dissociation?

Answer 4

• Bond breaking - +ve- Endothermic

Question 5

What is lattice association?

Answer 5

• Bond Formation- -ve- Exothermic

Question 6

What factors affect lattice enthalpy?

Answer 6

1 - Charge on the ions2 - Ionic radius (sheilding)

Question 7

How does ionic charge and ionic radius affect lattice enthlapy?

Answer 7

The greater the charge and the smaller the radius the stronger the electrostatic attractions therefore the greater the lattice enthalpy (high charge density)

Question 8

What is a Born-Haber cycle?

Answer 8

A type of Hess’s law cycle that enables us to calculate lattice enthlapy

Question 9

What is the enthalpy change of formation?

Answer 9

Formation of 1 mole of a substance from its constituent elements in standard states

Question 10

What is the enthalpy change of atomisation?

Answer 10

The standard atomisation enthalpy is the enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state. Enthalpy change of atomisation is always positive.

Question 11

What is the enthalpy change of ionisation energy?

Answer 11

(Metals) The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions

Question 12

What is the enthalpy change of electron affinity?

Answer 12

(Non-Metals) The energy required to add an electron to one mole of gaseous atoms

Question 13

What is the comparison of the born-haber and the perfect ionic model?

Answer 13

A comparison of experimental and theoretical calculated lattice enthalpy values

Question 14

How are the two models different?

Answer 14

Born haber uses experimental values to calculate lattice enthalpy and takes into account covalent character whereas the perfect ionic model assumes tehre is no covalent character, perfect ionic bonding and perfectly spherical ion.

Question 15

What is covalent character?

Answer 15

The movement of electrons causing the partial sharing of electrons in an ionic bond, it is increased when there is greater difference in charge and size of the ions

Question 16

When is there the biggest difference in experimental and theoretical values?

Answer 16

When covalent character is greater

Question 17

What is enthalpy of solution?

Answer 17

The enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution, e.g. a solid salt broken down into its ions in an aqueous state

Question 18

How is enthalpy of solution calculated?

Answer 18

enthalpy of lattice dissociation + the sum of all enthalpies of hydration

Question 19

What is enthalpy of lattice dissociation always?

Answer 19

Endothermic because bonds are being broken so delta H is positive

Question 20

What is the enthalpy of hydration?

Answer 20

The enthalpy change when 1 mole of gaseous ions forms aqueous ions

Question 21

What is enthalpy of hydration always?

Answer 21

Exothermic because it is the formation of bonds therefore delta H is negative

Question 22

How can you compare two elthalpies of solution?

Answer 22

The most negative enthalpy is most likely to be soluble because it releases energy when dissolved

Question 23

What is entropy?

Answer 23

a measure of disorder in a system measured in J.K^-1.Mol^-1

Question 24

When do you get an increase in entropy?

Answer 24

• Solid -> Liquid (melting)- Liquid -> Gas (boiling)- Dissolving- When theres an increase in number of moles

Question 25

How is entropy of a system calculated?

Answer 25

The sum of the entropy of the products - the sum of the entropy of the reactants

Question 26

Which reactions are more feasible?

Answer 26

Reactions with a positive entropy

Question 27

What is Gibbs free energy?

Answer 27

A measure of if a reaction is feasible

Question 28

What must delta G be, in order for a reaction to be spontaneous?

Answer 28

Below 0

Question 29

What is the delta G equation?

Answer 29

delta G = delta H - (T x delta S)

Question 30

What are the units of delta G?

Answer 30

J.Mol^-1

Question 31

What are the units of delta S?

Answer 31

J.K^-1.Mol^-1

Question 32

What are the units of delta H?

Answer 32

J.Mol^-1

Question 33

What are the units of T?

Answer 33

K

Question 34

How do you calculate the temperature of feasibility?

Answer 34

Assume delta G is 0

Question 35

Why might a reaction not occur even if it is feasible?

Answer 35

A reaction may not occur if there is a high activation energy

Question 36

What does delta G vary with?

Answer 36

Temperature

Question 37

How is the Gibbs free energy equation linked to the line equation?

Answer 37

y = delta Gmx = - delta S x Tc = delta H

Question 38

What happens when delta S is positive?

Answer 38

• Gradient is negative- Increase in entropy

Question 39

What happens when delta S is negative?

Answer 39

• Gradient is positive- Decrease in entropy

Question 40

In the Gibbs free energy graph, how is - delta s calculated?

Answer 40

From the graph, calculate the gradient

Question 41

In the Gibbs free energy graph, what does the x intercept represent?

Answer 41

The temperature at which the reaction becomes feasible.

Question 42

In the Gibbs free energy graph, how is gradient, T and dekta G linked?

Answer 42

The greater the gradient, the greater effect T has on delta G

Question 43

In the Gibbs free energy graph, what does the y intercept represent?

Answer 43

The delta H for the reaction