Thermodynamics

Question 1

State the definition of Enthalpy of Formation

Answer 1

Energy transferred when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kpa), all reactants and products being in their standard states

Question 2

State the definition of Enthalpy of Atomisation

Answer 2

Enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state

Question 3

State the definition of First Ionisation Enthalpy

Answer 3

Enthalpy change to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions (1+ charge)

Question 4

State the definition of 1st Electron Affinity

Answer 4

Enthalpy change when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous ions with a 1- charge.

Question 5

State the definition of 2nd Electron Affinity

Answer 5

Enthalpy change when 1 mole of gaseous -1 ions gain one electron per ion to form -2 gaseous ions

Question 6

State the definition of Enthalpy of lattice formation

Answer 6

Enthalpy change when 1 mole of an ionic crystal lattice is formed from it’s constituent gaseous ions under standard conditions

Question 7

State the definition of Enthalpy of lattice dissociation

Answer 7

Enthalpy change when 1 mole of an ionic crystal lattice is separated into its constituent gaseous ions under standard conditions

Question 8

State the definition of Enthalpy of dissociation

Answer 8

Enthalpy change when 1 mole of bonds of the same type of molecule in the gaseous state is broken

Question 9

State the definition of the Enthalpy of sublimation

Answer 9

Enthalpy change when a solid turns into gaseous atoms

Question 10

State the definition of the Enthalpy of hydration

Answer 10

Enthalpy change when 1 mole of gaseous ions becomes aqueous ions

Question 11

State the definition of the Enthalpy of solution

Answer 11

Enthalpy change when 1 mole of an ionic solid dissolves in a large enough amount of water to ensure dissolved ions are wells separated

Question 12

Why are Born Haber cycles useful?

Answer 12

It is useful to calculate lattice enthalpies. This is because we can’t calculate this directly from experiments

Question 13

What is the formula for Enthalpy of Formation

Answer 13

Enthalpy of formation = ∑ (Sum of all the other enthalpies)

Question 14

Why do Theoretical and experimental values of lattice enthalpies differ?

Answer 14

They can be different depending on how purely ionic the compound is. This is due some compounds showing more covalent character which leads to a larger difference in the values

Question 15

What does the perfect ionic model mean?

Answer 15

• Ions are spherical
• 100% Ionic
• Attractions are purely electrostatic

Question 16

What is the trend of lattice enthalpies down a group?

Answer 16

It gets less negative down any group

Question 17

What is Entropy?

Answer 17

Entropy (S) is the number of ways energy can be shared out between particles

Question 18

In terms of the 3 states of matter, which has the highest / lowest entropy?

Answer 18

Solids have lower entropies than liquids as the particles are arranged but gases have the highest entropy values as they are much disordered.

Question 19

What factors will lead to a change in entropy (∆S)?

Answer 19

• A change in state (solid
  
  • -> liquid or gas)
• If there is an increase in the No. Of moles produced compared to reactants; entropy increased

Question 20

What is the formula when calculating Change in Entropy?

Answer 20

∆S = ∑Sproducts - ∑Sreactants (Units = J K-1 mol-1)

Question 21

What is Gibbs free energy Change (∆G)?

Answer 21

Combines the effect of enthalpy and entropy determining the feasibility of a reaction

Question 22

What is the formula when calculating Gibbs Free Energy?

Answer 22

∆G = ∆H - T∆S

• ∆G = Jmol-1
• ∆H = Jmol-1
• Temp = K
• ∆S = J K-1 mol-1

Question 23

When is a reaction feasible

Answer 23

If ∆G is negative or zero