Enthalpy And Entropy

Question 1

Definition of Enthalpy change of hydration?

Answer 1

When one mole of gaseous ions dissolve in water to form one more of aqueous ions

Question 2

Definition of lattice Enthalpy?

Answer 2

Enthalpy change for the formation of one mole of an ionic compound from its gaseous ions under standard conditions

Question 3

Definition for Enthalpy change of formation

Answer 3

Enthalpy change when one mole of a compound is formed form it’s constituent elements under standard states and conditions

Question 4

Enthalpy change of atomisation

Answer 4

Enthalpy change to form one mole of gaseous atoms from the element under standard stated and conditions

Question 5

First ionisation energy

Answer 5

Enthalpy change to remove an electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 6

Electron affinity

Answer 6

Enthalpy change to add one electron to each atom in one mole of gaseous atoms to form one mole of 1- ions

Question 7

Why are successive electron affinities endothermic?

Answer 7

Requires adding an electron to a negative ion, therefore energy required to overcome repulsion

Question 8

Enthalpy change of soloution

Answer 8

Enthalpy change when one mole of a solute dissolves in a solvent

Question 9

What happens when a solute dissolves (Enthalpy change of soloution?

Answer 9

• Ionic lattice breaks up forming gaseous ions (negative lattice Enthalpy)
• Water molecules attracted to gaseous ions and surround them forming hydrated aqueous ions (Enthalpy change of hydration)

Question 10

Enthalpy change of hydration?

Answer 10

Enthalpy change when gaseous ions dissolve in water to form one mole of aqueous ions

Question 11

How does ionic size effect lattice Enthalpy and hydration Enthalpy

Answer 11

Down group radius increases
Attraction between ions decreases
Lattice Enthalpy / hydration Enthalpy becomes less negative
Melting point decreases

Question 12

How does ionic charge effect lattice Enthalpy and hydration Enthalpy

Answer 12

Across group ionic charge increases
Attraction between ions increase
Lattice Enthalpy/ hydration Enthalpy is more negative
Mp increases

Question 13

How do you predict solubility?

Answer 13

If the sum of the hydration Enthalpy is larger than lattice enthalpy it will dissolve

Question 14

Describe entropy

Answer 14

Tendency for energy to spread out and become more dissordered

Question 15

Standard entropy change

Answer 15

Entropy value for one mole of substance under standard states and conditions

Question 16

How to calculate entropy for a reaction?

Answer 16

Entropy of products minus entropy of reactants

Question 17

What is feasibility

Answer 17

Feasible if a reaction is able to occur spontaneously

Question 18

Free energy change

Answer 18

Overall energy change in a chemical reaction (considers Enthalpy and entropy)

Question 19

What’s gibs equation

Answer 19

Free energy=Enthalpy change -(temp in kelvin x entropy change)
G=H-TS

Question 20

What does free energy change tell us about feasibility

Answer 20

If Free energy change is <0 reaction is feasible

Question 21

What are limitations of using free energy to predict feasibility?

Answer 21

Reaction may not occur if free energy is negative but has a large activation energy or a slow rate