Thermodynamics

Question 1

Define lattice formation of enthalpy

Answer 1

Enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions

Question 2

Define lattice dissociation enthalpy

Answer 2

Enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions

Question 3

What does a big difference in theoretical and experimental enthalpy change tell you?

Answer 3

Shows ionic bonds are strongly polarised with a large degree of covalency

Question 4

Enthalpy change of formation

Answer 4

Enthalpy change when 1 mole of a compound is formed from its elements in their standard states

Question 5

Bond dissociation enthalpy

Answer 5

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

Question 6

Enthalpy change of atomisation of an element

Answer 6

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

Question 7

Enthalpy change of atomisation of a compound

Answer 7

Enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms

Question 8

1st ionisation energy

Answer 8

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

Question 9

2nd ionisation energy

Answer 9

Enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions

Question 10

1st electron affinity

Answer 10

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

Question 11

2nd electron affinity

Answer 11

Enthalpy change when 1 mole of gaseous 2- ions is made from 1 mole of gaseous 1- ions

Question 12

Enthalpy change of hydration

Answer 12

Enthalpy change when 1 mole of aqueous ions is formed from gaseous ions

Question 13

Enthalpy change of solution

Answer 13

Enthalpy change when 1 mole of an ionic substance dissolves enough solvent to form an infinitely dilute solution

Question 14

Define entropy

Answer 14

The measure of the disorder of a system

Question 15

Equation for S, entropy change

Unit?

What does a positive value for Ssystem tell you?

Answer 15

Ssystem = Sprod - Sreac

JK-1mol-1

Right side of the reaction is favoured

Question 16

What happens to entropy of temperature decreases?

If moles increase?

Answer 16

Entropy decreases

Entropy increase

Question 17

Define free energy change

Answer 17

Energy available for work, predicting whether reaction is feasible

Question 18

Equation for free energy change, G

Unit?

Answer 18

G = H - TS

H = enthalpy change, T = temp (K), S = entropy

Question 19

What value of G is required for a reaction to be feasible?

Answer 19

G = 0 or less

Question 20

Equation for total enthalpy change of a reaction

Answer 20

H = Hprod - Hreac (AS equation)

Question 21

How do u you find the temperature at which a reaction becomes feasible?

Answer 21

Make G = 0 and rearrange for T in the equation, G = H -TS