M5 - Enthalpy and Entropy

Question 1

Write an equation, with state symbols, for the enthalpy change of hydration for sodium (1)

Answer 1

Na+(g) + aq 🡪 Na+(aq)

Question 2

Write an equation to represent the atomisation of bromine (1)

Answer 2

½ Br2(l) 🡪 Br(g)

Question 3

What is the ‘Standard entropy change of a reaction’, ΔSθ:

Answer 3

The entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states

Question 4

Define ‘ First electron affinity’, ΔEA1Hϑ:

Answer 4

The enthalpy change when one electron is added to each atom in one mole of gaseous atoms, to form one mole of gaseous 1- ions

Question 5

Answer 5

B

Question 6

Answer 6

D

Question 7

Write an equation, with state symbols, for the lattice enthalpy of potassium chloride (1)

Answer 7

K+(g) + Cl-(g) 🡪 KCl(s)

Question 8

How would the entropy change during the enthalpy of solution of calcium oxide ?

Answer 8

Increase as 1 mole of solid is completely dissolved in water, forming more disordered aqueous ions

Question 9

Write the equation to calculate entropy change (1)

Answer 9

ΔSθ = ∑Sθ(products) - ∑Sθ(reactants)

Question 10

Define ‘Second electron affinity’, ΔEA2Hϑ

Answer 10

The enthalpy change when one electron is added to each ion in one mole of gaseous 1- ions, to form one mole of gaseous 2- ions

Question 11

Answer 11

A

Question 12

Would freezing water increase or decrease the entropy change?

Answer 12

Decrease, as solids have less disorder than liquids

Question 13

Write an equation, with state symbols, for the enthalpy of solution of NaCl (1)

Answer 13

NaCl(s) + aq 🡪 Na+(aq) + Cl-(aq)

Question 14

How would the entropy change when calcium carbonate reacts with hydrochloric acid?

Answer 14

Increase, as 1 mole of gas is formed from 0 moles of gas

Question 15

How is the temperature for reaction feasibility determined?

Answer 15

Set ΔG to be zero, and rearrange to;

T = ΔH / ΔS

Question 16

Define ‘Enthalpy change of atomisation’, ΔatHϑ:

Answer 16

The enthalpy change when the one mole of gaseous atoms is formed from its element, under standard conditions

Question 17

Answer 17

A

Question 18

What is the Gibbs equation?

Answer 18

ΔG = ΔH – TΔS

ΔG < 0 (-ve) Reaction is feasible
ΔG > 0 (+ve) Reaction is not feasible

Question 19

When is a reaction feasible/spontaneous in terms of ΔG ?

Answer 19

Only when ΔG is negative in value

Question 20

Write an equation to represent the second electron affinity of oxygen.

Answer 20

O-(g) + e- 🡪 O2- (g)

Question 21

Define ‘Standard Enthalpy Change of Solution’, ΔsolHϑ (1)

Answer 21

Enthalpy change that takes place when one mole of compound (solute) is completely dissolved in water under standard conditions (1)

Question 22

Write an equation to represent the first electron affinity for chlorine (1)

Answer 22

Cl(g) + e- 🡪 Cl-(g)

Question 23

Define ‘Lattice Enthalpy’, ΔLEH (1)

Answer 23

Enthalpy change when one mole of an ionic compound is formed from its gaseous ions (1)

Question 24

Answer 24

D

Question 25

Define ‘Standard Enthalpy Change of Hydration’, ΔhydHϑ (1)

Answer 25

The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions (1)

Question 26

What is meat by ‘Entropy’, S?

Answer 26

A measure of the dispersal of energy in a system. The entropy is greater when the system is more disordered. A system becomes energetically more stable when it becomes more disordered