Chemical Energetics II

Question 1

Factors affecting entropy

Answer 1

• Temperature
• Change in phase
• Change in no. of gaseous particles [Dominating]
• Mixing of particles (Gas, liquid, Dissolving ionic solid)

Question 2

Temperature (increase)

Answer 2

• Average KE of particles increase

- Move more randomly + vigorously

Question 3

Change in phase (Solid to liquid)) (Liquid to gas)

Answer 3

• Order of solid destroyed, liquid particles able to move freely + increased speeds
• Move more freely in larger volume of space

Question 4

Change in no. of gaseous particles (Products>Reactants)

Answer 4

Δn gas = n(gaseous products) - n(gaseous reactants)

…(g)

More gaseous products than gaseous reactants, more gas particles moving randomly

Question 5

Mixing of particles (Gas, liquid, Dissolving ionic solid)

Answer 5

Gas –> Expansion of gas to occupy container

Liquid –> Greater volume for molecule to move about

Dissolving ionic solid
- Giant ionic lattice break down to free moving ions (ΔS>0 )

• Free ions form ion-dipole attraction with water molecules (ΔS<0)

Question 6

Template to explain ΔS, entropy

Answer 6

• Factor responsible for change
• Leads to more ways of distributing particles and energies
• Results in greater disorder in system
• Entropy increase

Question 7

Gibbs Free Energy Change of Reaction

Answer 7

Refer to Image 1

Question 8

How Gibbs Free Energy Change of Reaction used to predict spontaneity of reaction?

Answer 8

Refer to Image 2

Question 9

Effects of temp. on spontaneity of reaction

Answer 9

Refer to Image 3

Question 10

Assumption made when seeing effects of temp. on spontaneity of reaction

Answer 10

• ΔH and ΔS relatively constant over small temperature range

- Not valid if change if phase of reactants or products when temp. varied

Question 11

Determining temp. for spontaneous rxn

Answer 11

ΔG < 0
ΔH - TΔS < 0
…