Study Notes: Chemical Reactions, Energy Changes, and Kinetics

Homework updates:
- Stoichiometry problems are key highlights for this week’s quiz.
- New homework on energy is due next Wednesday.
Exams and quizzes will be returned this Wednesday.

Definition:
- Gibbs Free Energy, denoted as ext{ΔG} , is a thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure.
Relevance:
- Determines spontaneity of chemical reactions.
- Related to three key concepts:
- ΔH: Change in enthalpy (heat absorbed or released).
  - Exothermic reactions (release heat) are favored, e.g., combustion (burning gasoline).
- ΔS: Change in entropy (disorder).
  - Positive ΔS: increased disorder (spontaneous processes, like gas escaping).
  - Negative ΔS: decreased disorder (non-spontaneous processes).
Favorability conditions:
- Both ΔH < 0 and ΔS > 0: always spontaneous.
- Both ΔH > 0 and ΔS < 0: always non-spontaneous.

Gibbs free energy equation: ext{ΔG} = ext{ΔH} - T ext{ΔS}
- Where:
- T: absolute temperature in Kelvin.
- Units: ext{Joules, ext{Kcal/mol}} for energy content.
Important notes:
- Low temperature: T ext{ΔS} becomes small, ext{ΔH} dominates.
- High temperature: T ext{ΔS} becomes larger than ext{ΔH} .

Low Temperature Scenario: Ice Freezing
- Freezing: Exothermic process (ΔH < 0) and negative change in disorder (ΔS < 0); favors formation of solid at low temperature.
High Temperature Scenario: Boiling Water
- Requires energy input (ΔG > 0) and entails an increase in disorder (ΔS > 0).
Importance of equilibrium: At equilibrium (ΔG = 0), forward and reverse reactions occur at equal rates.

ΔG > 0: Non-spontaneous (requires energy).
- Example: pushing a boulder uphill.
ΔG < 0: Spontaneous (natural progression toward product formation).
ΔG = 0: System at equilibrium (products and reactants at stable concentrations).

Exergonic vs. Endergonic:
- Exergonic: Negative ΔG, spontaneous; e.g., combustion, metabolism.
- Endergonic: Positive ΔG, non-spontaneous; e.g., charging a battery.
Algebra of Gibbs free energy allows mathematical evaluation of reactions.

Kinetics overview: Study of reaction rates and the changes that occur during reactions.
Activation Energy (Ea): Energy required to initiate a chemical reaction.
- The higher the activation energy, the slower the reaction (requires more energy to begin).

Temperature: Increased temperature generally increases reaction rate (10°C increase can double reaction rate).
Concentration:
- Higher concentration means more molecules available for collisions, thus increasing reaction rates.
Surface Area:
- More exposed surface area leads to faster reactions (e.g., small pieces of wood vs. large blocks).
Catalysts:
- Substances that speed up reactions without being consumed.
- They provide alternative reaction pathways with lower activation energy.

Concept of equilibrium: Reversible reactions can proceed in both directions.
- Dynamic equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction.
- Changes in concentration of reactants and products stabilize at a constant rate without changing overall quantities.
Visual representation: Charts and graphs depicting concentration increases for products and decreases for reactants until equilibrated.
Equilibrium constant (Kc): Ratio of concentration of products to reactants at equilibrium raised to their coefficients: K_c = rac{[Products]}{[Reactants]}
- Only includes gases and aqueous solutions; solids/liquids have concentration equal to one.
- Essential for determining reaction favorability and extent toward products or reactants.

Practical examples: Calculation exercises based on equilibrium constants and Gibbs free energy formulas to reinforce theoretical concepts.