Lesson Plans

Chemistry: The Central Science 9th Edition ©2003

by Brown, LeMay, and Bursten

Weeks 23–24: Chemical Thermodynamics

Chapter 19: Chemical Thermodynamics

This is a very important lesson, but it can probably be accomplished in less than the allotted two weeks.

College Board Performance Objectives:

• Define entropy in terms of randomness or disorder, and state the second law of thermodynamics.
• Predict the sign of the entropy of a given process, and state the third law of thermodynamics.
• Describe the effect of temperature and state changes on entropy.
• Calculate S° for a reaction using a table of absolute entropies, S°.
• Define free energy in terms of enthalpy and entropy and explain the relationship of the sign of G, and the spontaneity of a reaction.
• Calculate G° for a reaction using a table of G_f° for the reactants and products.
• Describe the conditions of "standard" state for standard free energy.
• Interconvert G° and K for a reaction.
• Describe the relationship between G and work.
• Calculate the free energy change for a reaction at nonstandard conditions, G, knowing G°, T, and the data needed to calculate Q.
• Predict how G changes with T, given the signs of H, and S.
• Estimate G° at any given temperature, given H° and S°.

College Board Lab Objectives:

Suggested Labs:

Resources:

• Instructor's Resource Manual, pp. 243–252
• Student's Guide, pp. 408–423
• Test Bank, pp. 639–674
• Instructor's Resource CD, Chapter 19

Pacing Guide:

• Spontaneity, Entropy and the Second Law—1 day
• Molecular Interpretation of Entropy—.5 day
• Calculation of S—.5 day
• Free Energy Change—.5 day
• Gibbs Free Energy and Its Calculation—.5 day
• G = H – TS—1 day
• G = G° + RT ln Q—1 day
• G = –RT ln K (K = e^–G°/RT)—1 day
• Block Scheduling
  Unlike acids and bases, this chapter should not take long to complete. Spontaneity, entropy, the second law, the molecular interpretation of entropy, and calculation of S could be covered in one block. Don't get too hung up on the molecular interpretation. Free energy and the Gibb's equation would take less than a block, whereas, the relationship between G, Q, and K will definitely take a whole block. Students must work suggested exercises!

Key Words:

Suggested Exercises:
Critical thinking questions and end-of-chapter activities are included in these exercises.

• pp. 768–775 , # 1, 3, 5, 13, 17, 19, 21, 23, 25, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 73, 77, 81, 83.
• eMedia Exercise: p. 775, # 101, 102, 104, 105.

Troubleshooting Tips/Error Traps:

• G_f° like H_f is relative to formation from elements, giving elements a zero value. S° is absolute entropy. A perfect crystal at absolute zero would have no entropy, thus have a zero value.
• The values given in the table of thermodynamic quantities are at 25°C (298.15 K). These values vary slightly with temperature.