Physical Chapter 6: Thermodynamics

Question 1

What is the symbol for enthalpy change?

Answer 1

ΔH

Question 2

What is enthalpy change defined as?

Answer 2

The heat energy transferred in a reaction at a constant pressure

Question 3

What is enthalpy change of formation?

Answer 3

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions

Question 4

What is enthalpy change of atomisation?

Answer 4

The enthalpy change when 1 mole of an element or compound in standard state is converted to gaseous atoms.

Question 5

What is lattice dissociation enthalpy?

Answer 5

The enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken

Question 6

What is first ionisation energy?

Answer 6

The enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms

Question 7

What is second ionisation energy?

Answer 7

The enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions.

Question 8

What is first electron affinity?

Answer 8

The enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms

Question 9

What is second electron affinity?

Answer 9

The enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions.

Question 10

What is enthalpy change of hydration?

Answer 10

The enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions

Question 11

What is enthalpy change of solution?

Answer 11

Enthalpy change when 1 mole of solute is dissolved in enough solvent that no further enthalpy change occurs on further dilution.

Question 12

What is lattice enthalpy a measure of?

Answer 12

Bond Strength

Question 13

How do we calculate lattice enthalpies?

Answer 13

Born-Haber Cycles

Question 14

What do you have to do to values for enthalpy if you are forming 2 moles in a born-haber cycle?

Answer 14

Double the value

Question 15

Why are theoretical lattice enthalpies often different from experimental values?

Answer 15

They asume a purely ionic model, where all ions are spherical. This doesn’t account for covalent character, where ions aren’t all spherical.

Question 16

What happens when you dissolve a substance in water?

Answer 16

The bonds between the ions break - endothermic
Bonds between ions and water are made - exothermic
Enthalpy of solution is the overall effect of these 2 changes

Question 17

What enthalpies do you use to calculate enthalpy of solution?

Answer 17

Lattice dissociation and enthalpy of hydration

Question 18

What is Entropy?

Answer 18

A measure of how disordered something is.
More directly, a measure of how many possible ways the particles can be arranged.

Question 19

Which state has highest entropy?

Answer 19

Gas

Question 20

What is the effect of an increased number of particles on entropy?

Answer 20

Entropy increases

Question 21

What is the effect of higher entropy in stability?

Answer 21

More stable

Question 22

How do you calculate entropy change for a reaction?

Answer 22

Entropy of products - entropy of reactants

Question 23

How do you measure the feasability of a reaction?

Answer 23

Gibbs Free Energy must be negative or 0.

Question 24

What is Gibbs Free energy?

Answer 24

ΔG = ΔH -TΔS
(temperature in kelvin)

Question 25

How do you find the temperature when a reaction is just feasible?

Answer 25

T = ΔH/ΔS
(rearrangement of ΔG formula)