B5 Energetics II

Question 1

Define Lattice Enthalpy

Answer 1

Enthalpy change that occurs with the formation of 1 mole of an ionic lattice from gaseous ions

Question 2

What is atomisation

Answer 2

Formation of 1mol of gaseous atoms from their elements

Question 3

Atomisation equation for iodine

Answer 3

Question 4

What is electron affinity

Answer 4

Formation of 1mol of gaseous anions from atomised elements and electrons

Question 5

First electron affinity of chlorine equation

Answer 5

Question 6

When must data be multiplied by 2 in a Born-Haber Cycle

Answer 6

When the product has a molar mass of two

Question 7

When calculating lattice enthalpy from a Born-Haber Cycle, how should the equation be structured

Answer 7

With enthalpy of formation of the left-hand side of the equation, and the route on the right

Question 8

Going clockwise round a Born-Haber cycle, what is the order of the processes

Answer 8

• Atomisations
• Ionisations
• Electron Affinities
• Lattice Enthalpy

Question 9

What must be remebered with electrons in Born-Haber Cycles

Answer 9

The electrons produced by ionisation energies, are used in the affinities

Question 10

Define Enthalpy Change of Solution

Answer 10

Dissolving of one mole of a solute in water

Question 11

Define Enthalpy Change of Hydration

Answer 11

Dissolving one mole of gaseous ions in water, to form aqueous ions

Question 12

Draw a solution enthalpy cycle, with general terms

Answer 12

Question 13

Draw a solution enthalpy cycle, for sodium chloride

Answer 13

Question 14

What is the affect on deltaT, and the enthalpy change of solution, when the volume of water in an experiment is doubled

Answer 14

• deltaT will half, as the same ammount of energy is transferred to double the volume of water
• Enthalpy of solution stays the same as the ratio of energy releases: moles, is the same, and so the same energy is released per mole

Question 15

What is the affect on deltaT, and the enthalpy change of solution, when the mass of the solid is doubled

Answer 15

• deltaT will double, as double the ammount of energy is being transferred to the same volume of water
• Enthalpy of solution stays the same, as the ratio of energy released: moles, is the same, and so the same ammount of energy is released per mole

Question 16

How does a greater ionic radius affect the attraction to ions

Answer 16

Weaker attraction to ions

Question 17

How does a smaller ionic radius affect the attraction to ions

Answer 17

Stronger attraction to ions

Question 18

How does a greater ionic charge affect the attraction to ions

Answer 18

Stronger attraction to ions

Question 19

How does a smaller ionic charge affect the attraction to ions

Answer 19

Weaker attraction to ions

Question 20

Explaination of comparing two lattice enthalpies with different ionic radii

Answer 20

• Lattice enthalpy of X is more exothermic than Y
• As ion X is smaller, so has a smaller ionic radius
• Therefore attraction to Z- ions are stronger
• So more energy is needed to break ionic bonds between ions

Question 21

Explaination of comparing two lattice enthalpies with different ionic charge

Answer 21

• Lattice enthalpy of X is more exothermic than Y
• As X has a 2+ charge, compared to Y which has a 1+ charge
• X has a greater ionic charge
• Therefore attraction is stronger to Z- ions
• So more energy is needed to break ionic bonds between ions

Question 22

Define entropy

Answer 22

The term used to describe the dispersal of energy (disorder) within the chemicals making up the chemical system

Question 23

Describe and explain how entropy changes from (s) to (l) [or (l) to (g)]

Answer 23

• Entropy increases
• As disorder increases
• As liquid particles have more disorder than solid particles

Question 24

Describe and explain how entropy changes from (l) to (s) [or (g) to (l)]

Answer 24

• Entropy decreases
• As disorder decreases
• As solid particles have less disorder than liquid particles

Question 25

Describe and explain how entropy changes when there are more moles of gas a products

Answer 25

* Entropy increases * As disorder increases * As more more gaseous molecules are produced

Question 26

Describe and explain what happens to entropy when there are less moles of gas in the products

Answer 26

* Entropy decreases * As disorder decreases * As less gaseous molecules are produced

Question 27

Equation to calculate deltaS

Answer 27

Question 28

Unit for entropy

Answer 28

Joules (J)

Question 29

Units for deltaS

Answer 29

J K(-1) mol (-1)

Question 30

Gibb's Free Energy Equation

Answer 30

Question 31

What is crucial to do when calculating Gibb's Free Energy

Answer 31

Always divide deltaS by 1000, so that it is in kJ

Question 32

What must be done when calculating Gibb's free energy with the units

Answer 32

Divide deltaS by 1000 so it is in kJ

Question 33

Why must deltaS be divided by 1000 when using it in Gibb's Free Energy equation

Answer 33

As deltaG is in kJ, and deltaS is in J

Question 34

Units for deltaG

Answer 34

kJ mol(-1)

Question 35

When is a reaction feasible

Answer 35

When deltaG is equal to/below zero

Question 36

When does the feasibility of a reaction change

Answer 36

When deltaG = 0

Question 36

Describe and explain how increasing temperature affects feasibility

Answer 36

* Feasibility increases, as temperature increases * As **-T**delta**S** becomes more negative than deltaH * So deltaG decreases

Question 37

Explain how Gibb's Free Energy is related graphically

Answer 37

Question 38

Draw a graph and annotate where: * Point where feasibility changes * deltaH * What the gradient represents

Answer 38

Question 39

What is the gradient when Gibb's Free Energy is graphical

Answer 39

**-** deltaS

Question 40

Why despite a reaction being feasible, will the reaction not occur

Answer 40

* The activation energy for the reaction is too high * Rate of the reaction is too slow