C22 Enthalpy And Entropy

Question 1

Define lattice enthalpy (must know)

Answer 1

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

Question 2

What does a more exothermic lattice enthalpy mean

Answer 2

More exothermic = more stronger ionic bonds

Question 3

Why’s it not possible to measure lattice enthalpy directly

Answer 3

It’s not possible to form 1 mole of ionic solid from its gaseous ions

Question 4

Define standard enthalpy change of solution

Answer 4

Enthalpy change that takes place when 1 mole of a solute is completely dissolved in water under standard conditions

Question 5

Define enthalpy change of hydration

Answer 5

The enthalpy change that takes place when dissolving 1 mole of gaseous ions in water

Question 6

What’s are the factors that impact the size of lattice enthalpy

Answer 6

Ionic size

Ionic charge

Ionic bond strength

Question 7

Which ions have more negative lattice enthalpy values? Smaller / larger ions? Why?

Answer 7

Smaller ions because they can get closer hence more stronger attraction

Question 8

Describe hydration

Answer 8

When an ionic lattice is broken the ions become part of the solution.

POS ions get attracted towards slightly neg oxygen and neg ions attracted towards slightly pos hydrogen

Question 9

What factors impact the magnitude of the hydration enthalpy

Answer 9

Ionic size

Ionic charge

Question 10

Define entropy

Answer 10

A measure of the dispersal of energy in a system which is greater when the system is more disordered

Question 11

What’s the symbol of entropy

Answer 11

S

Question 12

Solid or gas, which is more disordered

Answer 12

Gas

Question 13

What’s the unit of standard entropy

Answer 13

JK^-1 mol^-1

Question 14

How does temperature affect entropy

Answer 14

The greater temperature particles have more energy and move more. Thus the arrangement of particles become more random.

More random arrangement = higher entropy

Question 15

When a solid ionic lattice is dissolved in solution what happens to entropy

Answer 15

Entropy increases because the ions are more disordered

Question 16

How does change in number of gas molecules in a reaction affect entropy

Answer 16

Increase in number of gas molecules = increase in entropy

Decrease in number of gas molecules = decrease in entropy

Question 17

For a reaction to occur spontaneously delta G must be pos or neg

Answer 17

Negative

Question 18

What are the limitations of the predictions of feasibility made by using delta G

Answer 18

Reaction may have high activation energy

Rate of reaction may be very slow

Question 19

What does a more exothermic lattice enthalpy mean

Answer 19

More exothermic = more stronger ionic bonds

Question 20

Why is it not possible to measure lattice enthalpy directly

Answer 20

It is not possible to form 1 mole of ionic solid from its gaseous ions

Question 21

Define enthalpy change of solution

Answer 21

Enthalpy Change that takes place when 1 mole of a solute is completely dissolved in water under standard conditions

Question 22

Define enthalpy change of hydration

Answer 22

The enthalpy change that accompanies the dissolving of gaseous ions in water to form 1 mole of aq ions

Question 23

What are the factors that impact the size of lattice enthalpy

Answer 23

Size of ions involved

Charges on the ions

Ionic bond strength

Question 24

Which ions have more negative lattice enthalpy values? Smaller/larger ions? Why?

Answer 24

Smaller ions because they can get closer hence more stronger attraction

Question 25

Describe hydration

Answer 25

When an ionic lattice is broken the ions become part of the solution. Positive ions get attracted towards slightly negative oxygen and negative ions get attracted towards slightly positive hydrogen

Question 26

What are the factors that impact the magnitude of the enthalpy of hydration

Answer 26

Size of the ions Charge on the ions

Question 27

Is lattice enthalpy endo or exothermic

Answer 27

Exo Involves ionic bond formation from separate gaseous ions Value for Enthalpy change is always negative

Question 28

Define standard enthalpy change of formation (must know)

Answer 28

Enthalpy change that takes place when 1 mole of a compound is formed from its elements ender standard conditions, with all reactant and products in their standard states

Question 29

Define standard enthalpy of atomisation

Answer 29

Enthalpy change that takes places for formation of 1 mol of gaseous atoms from the element in its standard state under standard conditions

Question 30

Is standard enthalpy change of atomisation endo or exo

Answer 30

Endo Bonds are broken to form gaseous atoms

Question 31

Define 1st IE

Answer 31

Enthalpy change required to remove 1 electron from each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1+ ions

Question 32

Is IE endo or exo

Answer 32

Endo Energy required to overcome attraction between neg electron and pos nucleus

Question 33

How is electron affinity diff to IE

Answer 33

E affinity = measures energy to gain electrons IE = measures energy to lose electrons

Question 34

Define 1st E affinity

Answer 34

Enthalpy change that takes places place when 1 electron is added to each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1- ions.

Question 35

Is 1st e affinity endo or exo

Answer 35

Exo Electron being added is attracted towards nucleus

Question 36

Are 2nd e affinity endo or exo

Answer 36

Endo 2nd electron is being gained by a neg ion, which repels electron away So energy must be put into force negatively charged electron onto neg ion

Question 37

What happens when a salt dissolves in water

Answer 37

H2O molecules break up giant ionic lattice structure and overcome strong electrostatic attractions between opp charged ions

Question 38

Is Enthalpy change of solution exo or endo

Answer 38

Can be exo or endo

Question 39

Hoe to calc Enthalpy of solution

Answer 39

q=mc(triangle)T Calc moles of ionic lattice that dissolved q — n

Question 40

What 2 processes take place when solid ionic compound dissolves in water

Answer 40

Ionic lattice breaks up forming separate gaseous ions H2O molecules are attracted to and surround separate gaseous ions to form hydrated aq ions

Question 41

Is Enthalpy change of solution exo or endo

Answer 41

It can be endo or exo Depending on relative sizes of lattice enthalpy and enthalpy changes of hydration

Question 42

What are general properties of ionic compounds

Answer 42

High MP and BP Soluble in polar solvents Conduct electricity when molten or in aq

Question 43

What’s the effect of ionic size on MP

Answer 43

Ionic radius increases Attraction between ions decreases Lattice energy less negative MP decreases

Question 44

What’s the effect of ionic charge in MP

Answer 44

Ionic charge increases Attraction between ions increases Lattice energy becomes more neg MP increases

Question 45

Explain effect of ionic size on hydration Enthalpy

Answer 45

Ionic radius decrease Attraction between ion and water molecules decreases Hydration Enthalpy less negative

Question 46

Explain effect of ionic charge on hydration Enthalpy

Answer 46

Ionic charge increases Attraction with water molecules increases Hydration enthalpy becomes more neg (exo)

Question 47

What does a greater entropy mean

Answer 47

Greater dispersal of energy And greater the disorder

Question 48

Calc standard entropy

Answer 48

Products - reactants

Question 49

Gibbs equation

Answer 49

(Triangle)G = (triangle)H - T(triangle)S

Question 50

For reaction to be feasible

Answer 50

delta G < 0