Unit 9: “Thermodynamics and Kinetics” – Ch. 17 & 18

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INTRODUCTION:  When considering chemical reactions we are interested in two issues:  will the reaction occur and how fast will it occur.  The first question is a question of thermodynamics, the second question involves the kinetics of the reaction.  In this unit we will expand our understanding of chemical reactions to include the energy interactions and the factors that affect a reaction’s rate.  Energy in the form of heat, stored energy or energy gained from work done is essential when we consider whether two substances will react.  The difference between the stored energy (technically called internal energy or “enthalpy”) of reactants and products is observed and measured for chemical reactions.  A reaction, such as combustion, produces heat.  We use such reactions every day for cooking, for our automobiles, for electricity production.  Other reactions absorb heat and will feel cold to the touch when they occur.  Such reactions are used in such items as sports cold packs.  Other reactions produce heat in the form of light such as the glow sticks.  We will conclude our study of thermodynamics with a look at all the energy sources that contribute to the total amount of energy available for a chemical reaction.  This total amount of energy is called “free energy.”  The rate at which a reaction occurs is of tremendous interest for all chemists.  If a chemist wants to produce energy quickly, then the reaction must be rapid or the energy will dissipate before it can be of any use.  For example, the rusting of iron releases heat, but none of us have ever used the heat released by the rusting of our cars.  However, soldiers use the rapid rusting of iron to heat their food in MRE’s.  The question of rate is also very important for biological functions in our bodies.  Most of the reactions, which take place in our bodies, would occur so slowly that we would die before they did their job.  However, there is an important class of compounds in our bodies, which enables the life-essential reactions to occur rapidly.  This group of compounds is called enzymes and they are biological catalysts.  We will conclude this unit with a discussion of reaction kinetics including discussing catalysts.

OBJECTIVES: As you study this unit, you should learn and do the following:

  1. Distinguish between exothermic and endothermic reactions in terms of enthalpy change and how energy moves between a system and its surroundings.  (17.1)

  2. Describe how a calorimeter determines the heats of reactions and use one in an experiment.  (17.1 and lab exercise)

  3. Construct thermochemical equations and solve for enthalpy changes (DH) using the heats of reaction. (17.1)

  4. Define standard DH and how it is used. (17.2)

  5. Relate DH to changes of state and solve for energy changes in these reactions. (17.3)

  6. State Hess’ Law and apply it to determine DH for a reaction.  (17.4)

  7. Define what chemists mean by calling a chemical or physical process “spontaneous” or “non-spontaneous.”  (18.4)

  8. Identify two characteristics of spontaneous reactions and two factors that determine spontaneity of a reaction. (18.4)

  9. Define entropy and relate entropy changes to spontaneity.  Calculate entropy changes based on given data  (18.4 and Chem Activities)

  10. State the criterion for spontaneity in terms of free energy change.  (18.4) 

  11. Interpret and express the meaning of the rate of a chemical reaction.  (18.1)

  12. Explain how the temperature, concentration, particle size of reactants and catalysts influence the rate of a chemical reaction using collision theory.  (18.1)

  13. Discuss the relationship of a mechanism to a chemical reaction and relate the mechanism to the potential energy diagram of the reaction.  (18.5)

  14. Identify an intermediate, catalyst and the rate-determining step from a reaction mechanism and potential energy diagram. (18.5)

LEARNING ACTIVITIES:

To learn about objectives 1- 6:

To learn about objectives 7-10:

To learn about objectives 11-14:

To make sure you understand the objectives for this unit:

Deadlines:

            Quiz on Ch. 17:

            TEST on Unit 9:

GO TO SELF-TEST