Ch. 6 - Thermodynamics and KineticsSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

You might have heard of the terms thermodynamics and kinetics before, but in chemistry they mean something very specific. Free energy diagrams are going to give us a snapshot of what these terms mean. 

Concept #1: Introduction to free energy diagrams. 

Atoms save energy by forming bonds. Free energy diagrams show overall changes in potential energy during reactions.

Free energy diagrams give us information on the spontaneity and rate of reactions:

  • Thermodynamics describes favorability. Determined by Gibbs Free Energy (ΔG° = ΔH° - TΔS).
  • Kinetics describes rate. Determined by the activation energy of the rate determining step (Ea).

Example #1: Describe the favorability and rate of the following free energy diagram.

Example #2: Describe the favorability and rate of the following free energy diagram.

Example #3: Describe the favorability and rate of the following free energy diagram.

Example #4: Describe the favorability and rate of the following free energy diagram.

Additional Problems
Draw the following energy diagram with the following requirements: A reaction that has 3 steps and overall is exergonic. Steps 1 and 2 are endergonic, Step 3 is exergonic. Step 2 is the rate determining step.  
The accompanying diagram, which describes the fate of the intermediate in a reversible reaction, implies that: A) the less stable product forms more rapidly. B) the more stable product forms more rapidly. C) product B will predominate at equilibrium. D) the intermediate has a short lifetime. E) No conclusions can be drawn as to either reaction rate or product stability.
For a 2 step reaction represented by the following reaction energy diagram which of the following statements is true? A)        Reaction is fast, product is in high yields B)        Reaction is fast, product is in low yields C)        The second step is fast and product is formed in low yields D)        The forward reaction has better yields than the reverse reaction 
Which of the following energy diagrams is of a reaction with one transition state?
Draw an energy diagram of a reaction with the following characteristics: A one-step reaction with a negative ΔG.
Draw an energy diagram of a reaction with the following characteristics: A one-step reaction with a positive ΔG.
Draw an energy diagram of a reaction with the following characteristics: A two-step reaction with an overall negative ΔG, where the intermediate is higher in energy than the reactants and the first transition state is higher in energy than the second transition state.  
Consider the following four energy diagrams: Which diagrams correspond with a two-step mechanism?
Consider the following four energy diagrams: Which diagrams correspond with a one-step mechanism?
Consider the following four energy diagrams: Compare energy diagrams A and C. Which has a relatively larger E a?
Consider the following four energy diagrams: Compare diagrams A and C. Which has a negative ΔG?
Consider the following four energy diagrams: Compare diagrams A and D. Which has a positive ΔG?  
Consider the following four energy diagrams: Compare all four energy diagrams. Which one exhibits the largest E a?
Consider the following four energy diagrams: Which processes will have a value of K eq that is greater than 1?
Consider the following four energy diagrams: Which process will have a value of K eq that is roughly equal to 1?
Identify all transition states and intermediates on the following energy diagram:
For the one step transformation shown below, draw a potential energy level diagram. Indicate transition states as “TS”. You need not draw the transition state structure or indicate if the TS is early or late along the reaction coordinate.
The activation energy of a slow reaction is A. negative.  B. low.  C. high.  D. dependent on temperature. 
For the following reaction, answer the following questions: a. Estimate the activation energy (provide both value and unit) b. Does the graph represent an endothermic or exothermic reaction? c. Determine the enthalpy (ΔH) for the reaction product.
The activation energy for this step is 76 kJ/mol (18.3 kcal/mol). Sketch a potential energy diagram for this step, labeling reactants, products, and transition state. 
According to the diagram, the activation energy of the slow step is given by the energy difference between statesA. 1 and 2B. 2 and 3C. 3 and 4D. 1 and 5 
Transition states have partially formed bonds whereas intermediates have fully formed bonds ( True or False )
Which of the following would not typically be true for a reaction after adding a catalyst? a. The reaction rate would increase. b. The time to complete the reaction would decrease.c. The activation energy would decrease.d. The reaction would proceed by an alternate pathway.e. The catalyst would be consumed at the same rate that reactants are consumed.