Chemistry Notes on Chapters 18 and 19

Chapter 18 Summary

• Key Topics:
  • Completion of Chapter 18, covering dissolution reactions and equilibrium constants.
  • Introduction to Chapter 19 focusing on the first three laws of thermodynamics.
• Mastering Chemistry and Quizzes:
  • Chapter 18 Assignment: Due on Saturday.
  • Quiz 5: Scheduled for Sunday.
• Insoluble Salts:
  • Discussed how to write dissolution reactions for salts.
  • Ksp (Solubility Product Constant):
  • General formula:
    $K<em>{sp} = [ ext{Ag}^+]^2 imes [ ext{CrO}</em>4^{2-}]$
  • Only products are included as reactants are solids.
  • Relationship between molar solubility (s) and Ksp:
  • $K_{sp} = 4s^3$ for 1:1 salts.
• Common Ion Effect:
  • The presence of a common ion (e.g., $ext{Ag}^+$ from $ext{AgNO}_3$) shifts equilibrium, decreasing molar solubility.
• Dissolving in Different Solutions:
  • Dissolution in aqueous solutions vs. common ions affecting solubility (use ICE tables to find new equilibrium concentrations).
  • Example: Dissolution of silver chromate in silver nitrate leading to a reduced solubility.

Chapter 19 Introduction: Thermodynamics

• Spontaneity and Thermodynamics:
  • Reactions with negative ΔH (exothermic) generally tend to be spontaneous but entropy (ΔS) also influences this tendency.
• First Law of Thermodynamics:
  • Total energy is conserved; energy in equals energy out (
    $ext{Energy}<em>{ ext{in}} = ext{Energy}</em>{ ext{out}}$).
  • Example with formation reactions (e.g., water). Standard states for hydrogen and oxygen must be defined.
• Calculating ΔH of Reactions:
  • Use:
    $ΔH<em>{reaction} = ext{Σ}(ΔH</em>f ext{products}) - ext{Σ}(ΔH_f ext{reactants})$
  • Example of water freezing: Calculate ΔH_f using standard enthalpy values.

Entropy and Gibbs Free Energy

• Entropy Change (ΔS):
  • Determine from energy change at a given temperature:
    ext{ΔS} = rac{ ext{ΔH}}{T}
  • Relationships to determine spontaneity of the reaction based on system and surroundings.
• Second Law of Thermodynamics:
  • Entropy of the universe increases for spontaneous reactions; thus, ΔS of universe must be greater than zero.
  • Relation to process: freezing of water leads to a decrease in entropy of the system (negative ΔS), but has a higher entropy in surroundings due to heat released.
• Gibbs Free Energy (ΔG):
  • Defined as:
    $ΔG = ΔH - TΔS$
  • Insights on spontaneity:
  • Favorable Conditions:
    • ΔH < 0 (exothermic), ΔS > 0 (increase in disorder), ΔG < 0 (spontaneous).
• Third Law of Thermodynamics:
  • Entropy of a pure crystalline substance is zero at absolute zero (0 K).

Exam Preparation Notes

• Review Ksp expressions for various dissociation reactions.
• Practice using ICE tables for solubility problems with common ions.
• Understand and apply Gibbs free energy equations for predicting spontaneity in chemical reactions.