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# Entropy

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Sections
Spontaneous vs Nonspontaneous Reactions
Entropy
Entropy Calculations
Entropy Calculations: Phase Changes
Third Law of Thermodynamics
Gibbs Free Energy
Gibbs Free Energy Calculations
Gibbs Free Energy And Equilibrium

Entropy deals with the randomness, chaos and disorder in the universe

###### Understanding Entropy

Concept #1: Entropy represents the unused and lost energy during an energy transformation.

Example #1: The second law of thermodynamics leads us to conclude:

a) the total energy of the universe is constant

b) the disorder of the universe is increasing with the passage of time

c) the total energy of the universe is increasing with time

d) the total entropy of the universe is decreasing with time

Concept #2: Standard molar entropy examines a substance's randomness under standard conditions.

Concept #3: There are 3 main factors that can increase entropy.

Example #2: Select a substance with greatest molar entropy.

a) P4 (s)            b) H2O (l)          c) NH3 (g)          d) Li2 (s)            e) CO(g)         f) SO3 (g)

Concept #4: In terms of entropy, greater freedom of movement means greater entropy.

Example #3: Predict how the entropy of the system is affected in the following process:

1) CH(g, 125°C) →  CH(g, 200°C).

2) KClO3 (s) (7 L container) → KClO3 (l) (3 L container)

Concept #5: Under chemical changes, creating more products than reactants leads to greater entropies.

Example #4: Which one of the following reactions produces a decrease in the entropy of the system?

a) KCl (s) → K+ (aq) + Cl- (aq)

b) 2 CO (g) + O2 (g) → 2 CO2 (g)

c) CH3OH (l)  →  CO (g)  +  2 H2 (g)

d) C6H12O6 (s) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (l)

Practice: Which reaction is most likely to have a positive ∆S of reaction?

a) SiO2 (s)  +  3 C (s)  →  SiC (s)  +  2 CO (g)

b) 6 CO2 (g)  +  6 H2O (g)  → C6H12O6 (s)  +  6 O2 (g)

c) CO (g)  +  Cl2 (g)  → COCl2 (g)

d) 3 NO2 (g)  +  H2O (l)  → 2 HNO3 (l)  +  NO (g)

Practice: Identify sign of entropy changes for the following processes.

1) freezing water to form ice

2) ideal gas allowed to expand in a closed container at constant T

3) mixing of two gases into one container

4) NH2 (g) (1atm) → NH2 (g) (3 atm)

5) gas mixture transferred from larger to smaller container

Practice: Select correct statement(s) below:

a) gaseous CO2 has higher entropy in 2 L container compared to in 5 L container

b) N2O (g) contains higher standard molar entropy then HI (g)

c) NaHCO3 (aq) + HC2H3O2 (aq) → NaC2H3O2 (aq) + H2O (l) + CO2 (g) has a negative ∆S

d) evaporation of water at 100 °C involves greater ∆S than evaporation at 112 °C