entropy

Question 1

What is enthalpy of lattice formation?

Answer 1

The enthalpy change when one mole of an ionic compound is formed from its constituent ions in the gaseous state
it is exothermic
∆lattH* or ∆leH
Mg 2+(g) + 2 Cl- (g) > MgCl2(s)

Question 2

What is enthalpy of lattice dissociation

Answer 2

The enthalpy change when one mole of an ionic compound is separated into its component gaseous ions
It is endothermic
/\ledH*
MgCl2(s) -> Mg2+(g) + 2 Cl (g)

Question 3

What is the standard enthalpy of atomisation

Answer 3

The enthalpy change for the formation of one mole of gaseous atoms from the element in its standard state.
/\atH* it is endothermic
1/2 l 2(g) -> I(g) or Na(s) -> Na(g)

Question 4

What is bond dissociation Enthalpy?

Answer 4

The enthalpy change when one mole of a covalent bond is broken under standard conditions in the gaseous state.
It is endothermic.
/\disH
I2(g) -> 2 l(g)

Question 5

What is first ionisation enthalpy?

Answer 5

Enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous ions with a single positive charge.
Mg(g) -> Mg+(g) + e-

Question 6

What is second ionisation enthalpy?

Answer 6

Enthalpy change when one mole of electrons is removed from one mole of gaseous ions with a single positive charge to form one mole of gaseous ions with a 2+ charge.
Mg+(g) -> Mg 2+(g) + e-

Question 7

What is first electron affinity?

Answer 7

The enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single negative charge.
is exothermic
O(g) + e- -> O-(g)

Question 8

What is second electron affinity?

Answer 8

• The enthalpy change when one mole of gaseous ions with a single negative charge forms one mole of gaseous ions with a double negative charge.
• Second electron affinity value is always positive, therefore endothermic. as There is repulsion between the negative ion and the negative electron being added.
  0-(g) + e- > 0-2(g)

Question 9

What is Enthalpy of solution

Answer 9

Enthalpy change when one mole of an ionic solid dissolves in an amount
of water large enough so that the dissolved ions are well separated and dont interact with each other.
Is exothermic if enthalpy of hydration is higher than lattice enthalpy
∆solH*
MgCl2(s) + aq -> Mg2+(aq) + 2 Cl- (aq)

Question 10

What is enthalpy change of hydration

Answer 10

the enthalpy change when gaseous ions dissolve in water to form one mole of aqueous ions.
is exothermic
∆hydH*
Mg2+(g) + aq -> Mg2+(aq)

Question 11

Factors affecting hydration:

Answer 11

• The higher the ionic radius, the smaller the attraction between ions and water molecules so hydration energy is less negative
• The higher the ionic charge, the higher the attraction between ions and water molecules; hydration energy becomes more negative

Question 12

what is lattice enthalpy

Answer 12

the Enthalpy change that the companies the formation of 1 mol of ionic lattice from gaseous ions,
its endothermic
/\lattH

Question 13

Factors affecting lattice enthalpy:

Answer 13

• The higher the ionic radius, the smaller the attraction between ions so lattice enthalpy is less negative and melting points decrease
• The higher the ionic charge, the higher the attraction between ions; lattice energy becomes more negative and melting points increase

Question 14

what is entropy (S in J/k/mol)

Answer 14

A measure of the dispersal of energy in a system Which is greater when the system is more disordered (Highest when it’s gas or when it has higher Mr)

Question 15

How does temperature affect entropy

Answer 15

The greater the temperature particles have more energy and move more so the arrangement of particles becomes more random and more disordered therefore they have a higher entropy - gases have the highest entropy

Question 16

Equation to calculate entropy change

Answer 16

/\S = products - reactants

Question 17

What is the Gibbs free energy equation And what do we use it for

Answer 17

/\G = /\H - T/\S
/\G - Gibbs free energy
/\H - Enthalpy change
T - temp (K)
/\S - Entropy change
We use it to see if a reaction is feasible (It’s feasible if /\G < 0)

Question 18

What are the limitations of the predictions of feasibility using /\G

Answer 18

The reaction is feasible but it still may not occur spontaneously because:
- Reaction may have high activation energy
- rate of reaction may be very slow

Question 19

N2 + 3H2 -> 2HN3 Explain the entropy change in this reaction

Answer 19

Entropy will decrease as there are less moles of gas in the products so decrease in randomness of particles, energy is less dispersed

Question 20

What is the standard entropy of a substance S*

Answer 20

The entropy of one mole of a substance under standard conditions