Chem 162 - Ch 12 - Entropy

Chapter 1: Introduction to Entropy

• Thermodynamics Overview: Review of enthalpy (Delta H) as a state function indicating changes in energy.

  • Enthalpy is defined as the heat (Q) of a chemical reaction.

  • Positive Delta H indicates endothermic reactions; negative Delta H indicates exothermic reactions.

• Transition to Entropy: Moving from enthalpy to entropy definitions.

  • Entropy: Not a measure of energy, but of energy dispersal—how spread out energy is.

  • Relationship to Chapters 9 & 12: Both chapters cover thermodynamic principles.

  • Chapter 9 focuses on enthalpy, while Chapter 12 introduces entropy.

Chapter 2: Positive Entropy Change

• Second Law of Thermodynamics: Total entropy in a system and its surroundings increases in spontaneous processes.

• Understanding Entropy Change: Example of phase change from solid to liquid:

  • Solid water (ice) has low molecular motion compared to liquid water, which has increased motion.

  • Positive entropy change occurs as solid transitions to liquid.

  • Reverse process (liquid to solid) denotes negative entropy change.

Chapter 3: Phases of Liquid and Gas

• Situations of Increasing Entropy:

  1. Phase change from solid to liquid or gas.

  2. Phase change from liquid to gas.

• Mole Relationships:

  • Increase in the number of gas moles during a reaction results in increased entropy.

  • More gas moles means increased energy dispersal.

Chapter 4: Delta S and Gas Moles

• Entropy Calculations: Evaluating changes in entropy for reactions.

  • Positive Delta S signifies increasing entropy; negative Delta S signifies decreasing entropy.

• Example of Gas Mole Change:

  • Reaction with zero moles of gas as reactants producing one mole of gas; results in positive Delta S.

Chapter 5: Overall Entropy Change with Reactions

• Cellular Respiration Example: Uses chemical potential energy for biological functions.

  • Reaction Formula: C6H12O6 + 6O2 (reactants) ➔ 6CO2 + 6H2O + ATP (products).

  • Initial reactants (7 molecules): Glucose + O2; Products (12 molecules): CO2 + H2O increases energy dispersal.

• Visualizing Entropy: Comparing ball count in a container before and after the reaction to see increased disorder.

Chapter 6: Conclusion

• Homework Resources: Guidelines in SmartWorks, PowerPoint lectures, and textbooks to practice predicting entropy change signs.

  • Increasing disorder/dispersal corresponds with positive entropy change.

  • Decreasing disorder/dispersal corresponds with negative entropy change.

• Future Topics: Upcoming calculations for determining absolute entropy values.