Chapter 22 - Enthalpy and Entropy Flashcards Preview

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Flashcards in Chapter 22 - Enthalpy and Entropy Deck (31)
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1
Q

Define lattice enthalpy

A

The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.

2
Q

What kind of energy change will lattice enthalpy always be?

A

Exothermic

Enthalpy change is negative

3
Q

What is the Born-Haber cycle?

A

A way of indirectly calculating lattice enthalpy from other known energy changes.

4
Q

What is the formation of gaseous atoms and what energy change is it?

A

Changing elements in their standard states into gaseous atoms.
Endothermic as it involves bond breaking.

5
Q

What is the formation of gaseous ions and what energy change is it?

A

Changing gaseous atoms into positive and negative gaseous ions.
Endothermic.

6
Q

What is the lattice formation and what energy change is it?

A

Changing gaseous ions into the solid ionic lattice.

Exothermic.

7
Q

Define standard enthalpy change of formation

A

The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states.

8
Q

Define standard enthalpy change of atomisation

A

The enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions.

9
Q

Define first ionisation energy

A

The enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

10
Q

Why is ionisation energy always endothermic?

A

Energy is required to overcome the attraction between a negative electron and a positive nucleus.

11
Q

Define first electron affinity

A

The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.

12
Q

Why is first elctron affinity always exothermic?

A

Electron being added is attracted in towards the nucleus.

13
Q

Why are successive electron affinities endothermic?

A

The negative ion repels the additional electron, so energy is required to force the electron onto it.

14
Q

Define standard enthalpy change of solution

A

The enthalpy change that takes place when one mole of a solute dissolves in a solvent.

15
Q

What processes take place when a solid ionic compound dissolves in water?

A

Ionic lattice breaks up

Water molecules are attracted to and surround the ions.

16
Q

What are the energy changes involved in these processes of a solid ionic compound dissolving in water?

A

Ionic lattice is broken up forming separate gaseous ions.
Separate gaseous ions interact with polar water molecules to form hydrated aqueous ions.
Called enthalpy change of hydration.

17
Q

Define enthalpy change of hydration

A

The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions.

18
Q

Describe the effect of ionic size on lattice enthalpy and melting point

A

Ionic radius increases
Attraction between ions decreases
Lattice enthalpy becomes less negative
Melting point decreases

19
Q

Describe the effect of ionic charge on lattice enthalpy and melting point

A

Ionic charge increases
Attraction between ions increases
Lattice enthalpy becomes more negative
Melting point increases

20
Q

Describe the effect of ionic size on hydration enthalpy

A

Ionic radius increases
Attraction between ion and water molecules decreases
Hydration energy less negative

21
Q

Describe the effect of ionic charge on hydration enthalpy

A

Ionic charge increases
Attraction with water molecules increases
Hydration energy becomes more negative

22
Q

Why is hydration enthalpy an inaccurate method of predicting solubility?

A

Many compounds with endothermic enthalpy changes of solution are soluble.

23
Q

Define entropy

A

A measure of the dispersal of energy within the chemicals in a chemical system.

24
Q

What are the units of entropy?

A

J/K/mol

25
Q

How does entropy relate to physical states?

A

In order of size:
Gases > liquids > solids
for entropy value

26
Q

Define standard entropy

A

The entropy of one mole of a substance, under standard conditions.
(Always positive)

27
Q

How is an entropy change calculated for a reaction?

A

Change in entropy is the sum of the entropies of the products minus the sum of the entropies of the reactants.

28
Q

What is feasibility?

A

Whether a reaction is able to happen and is energetically feasible (or spontaneous).

29
Q

What is the equation for free energy change?

A

ΔG = ΔH - TΔS

30
Q

What is the requirement for the free energy change such that a reaction is feasible?

A

ΔG < 0

A decrease in free energy.

31
Q

Even though a reaction may have a negative value for ΔG, why might the reaction not take place at room temperature?

A

High activation energy resulting in a very slow rate.