TOPIC 13 - Energetics II

Question 1

What is lattice enthalpy of formation?

Answer 1

Question 2

What is enthalpy chaange of atomisation?

Answer 2

Question 3

What is 1st electron affinity?

Answer 3

Question 4

What is 2nd electron affinity?

Answer 4

Question 5

Why are Born-Haber cycles useful?

Answer 5

To calculate enthalpies that can’t be measured experimentally.

Question 6

What is A?

Answer 6

Enthalpy of formation

Question 7

What is B?

Answer 7

Enthalpy of atomisation of chlorine

Question 8

What is C?

Answer 8

Enthalpy of atomisation of lithium

Question 9

What is D?

Answer 9

1st ionisation energy of lithium

Question 10

What is E?

Answer 10

1st electron affinity of chlorine

Question 11

What is F?

Answer 11

Lattice enthalpy of formation of LiCl

Question 12

Calculate lattice enthlapy of LiCl using the Born-Haber cycle

Answer 12

Question 13

What is a perfectly ionic model?

Answer 13

Ions are evenly spherical in the latticeand the charge is evenly distributed (point charge)

Question 14

Why are all the experimental values higher than the theoretical ?

Answer 14

None of them is purely ionic. There is some covalent character. The electron cloud in the anion is distorted so electrons are closer to the +ve charge, so more energy is released.

Question 15

Are smaller cations more or less polarising? Why?

Answer 15

More polarising.

In smaller cations, the +ve charge is closer to the electrons in the anion and so electrostatic forces of attraction are greater and the electron cloud is distorted more.

Question 16

Are cations with bigger charge more or less polarising?

Answer 16

More polarising.

Bigger charge = bigger electrostatic forces of attraction = electron cloud in anion is distorted more.

Question 17

Are bigger anions more or less polarisable? Why?

Answer 17

More polarisable.

Electron cloud is further away from the nucleus of the anion and so electrons are more attracted to the nucleus of the cation, so electron cloud is more distorted.

Question 18

What is the general rule for electronegativity in the periodic table?

Answer 18

Further up and right you go, electronegativity increases (excluding nobel gases).

Question 19

How does difference in electronegativity affect the nature (ionic/covalent) of the bond?

Answer 19

The bigger the difference between the two atoms, the more ionic the bond is.

Question 20

What is enthalpy change of solution?

Answer 20

Question 21

What happens, in terms of bonds, for a substance to dissolve?

Answer 21

Substance bonds break - endothermic.

Bonds fromed between solvent and substance - exothermic.

Question 22

For a substance to dissolve, what must the strength of the newly formed bonds be?

Answer 22

Same strength or greater than those broken previously.

Question 23

What enthalpy of solution does a soluble substance have?

Answer 23

-ve enthalpy of solution (exothermic).

Question 24

What is enthalpy of hydration?

Answer 24

Question 25

What is A?

Answer 25

Enthalpy change of solution

Question 26

What is B?

Answer 26

Lattice dissociation enthalpy

Question 27

What is C?

Answer 27

Enthalpy of hydration

Question 28

How does the charge of the ions affect enthalpy of hydration?

Answer 28

Question 29

How does size of ions affect the enthalpy of hydration?

Answer 29

Question 30

What is entropy?

Answer 30

The number of ways energy can be spread out between particles. It is a measure of disorder in a system.

Question 31

Can an enthapically unfavourable reaction be spontaneous (feasible)?

Answer 31

Yes. If the change in entropy overcomes the change in enthalpy i.e.

Question 32

What is the equation for the entropy change of a reaction?

Answer 32

Question 33

What are the standard conditions for standard entropy?

Answer 33

Question 34

Does entropy increase or decrease in an entropically feasible reaction?

Answer 34

Increases.

Question 35

What is the equation for total entropy change?

Answer 35

Question 36

Answer 36

Question 37

What is the equation for Gibbs free energy?

Answer 37

Question 38

How does gibbs free energy tell if a reaction is feasible at that temperature?

Answer 38

If gibbs is 0 or -ve, reaction is feasible.

Question 39

Why might a reaction not be observed even though it is feasible?

Answer 39

The reaction might have high activation energy and/or a slow rate of reaction.

Question 40

Is a reaction feasible if it has a -ve enthalpy change and a +ve entropy change?

Answer 40

Yes. It is feasible at any temperature. Gibb's free energy is -ve at any temperature.

Question 41

Is a reaction feasible if it has a +ve enthalpy change and a -ve entropy change?

Answer 41

Never feasible. Gibb's energy will always be positive

Question 42

Is a reaction feasible if it has a -ve enthalpy change and a -ve entropy change?

Answer 42

Only at lower temperatures. Gibb's free energy will only be negative in lower temperatures.

Question 43

Is a reaction feasible if it has a +ve enthalpy change and a +ve entropy change?

Answer 43

Only at higher temperatures. Gibb's free energy is will only be -ve at higher temperatures.

Question 44

How do you calculate the temperature at which a reaction becomes just feasible?

Answer 44

Question 45

What are the values for Kc for reactions with a -ve change in gibbs free energy?

Answer 45

Kc is large (greater than 1) because reaction feasible.

Question 46

What are the values for Kc for reactions with a +ve change in gibbs free energy?

Answer 46

Kc is less than 1. The reaction isn't feasible.

Question 47

What is the equation linking gibb's free energy and Kc?

Answer 47