U1.4: Entropy and Spontaneity

Question 1

Formula for entropy (∆ S) and units?

Answer 1

Delta S (J K^-1 mol^-1) = SUM(Products - Reactants)
- Same as enthalpy change of formation formula

Question 2

Define entropy (∆ S)

Answer 2

• the distribution of available energy among the particles

Question 3

Start the relationship between order and the entropy

Answer 3

• The greater the disorder of the system the higher the entropy, and the more spread out the particles are

Question 4

What is the level of entropy in gases and solids

Answer 4

• Gases have high enthalpy (highly disordered)
• Solids have low enthalpy (lowly disordered)

Question 5

State the 2nd law of thermodynamics

Answer 5

The total entropy of the universe tends to increase; Chaos, preferred by nature, is spontaneous whist order requires effort.

Question 6

State the 3 ways a chemical reaction can have high entropy

Answer 6

1. Exothermic
2. Number of particles (moles)
3. Change of state (if same state and same # of particles, entropy is the same)

Question 7

What is the relationship between number of particles in products and reactants and entropy?

Answer 7

products > # of reactants = + Entropy (greater disorder)
# products < # of reactants = - Entropy (less disorder)

Question 8

Define standard free energy change (Gibbs free energy)

Answer 8

A measure of the quality of the energy available

Question 9

Formula for standard free energy change and units?

Answer 9

∆ G (in kJ mol -^1) = ∆ H - Total ∆ S

Question 10

State the value at which ∆ G has to be in for a reaction to start

Answer 10

∆ G = 0 (Equlibrium)
∆ G = - (for a reaction to start)

Question 11

State what reaction is favoured when ∆G<0, ∆ G>0 and when ∆ G=0

Answer 11

∆G<0
- Reaction is spontaneous in the forward direction (Favours formation of products)

∆G>0
- Reaction is non-spontaneous in the forward reaction (Favours formation of reactants)

∆G=0
- Reaction is at equilibrium (constant formation of reactants and products)

Question 12

Formula for ∆Gfø, ∆Hfø and ∆Sø

Answer 12

• ∆Gø = ∑∆Gøf(P-R)
• ∆Hø = ∑∆Høf(P-R)
• ∆Sø = ∑SGøf(P-R)