Chemistry - A Molecular Science

Chapter 9 Reaction Energetics

formation of the transition state of the reac

tion. The frequency of collisions between two

particles is expressed in terms of the product of their molar concentrations. The fraction of these collisions that yield the transition stat

e depends upon the activation energy of the

reaction, the thermal energy of the reacting molecules, and the orientation of the reacting molecules when they collide

.

Equilibrium is established when the products

and reactants reach the transition state at

the same rate. Solute concentrations and

gas pressures in an equilibrium mixture are

dictated by the equilibrium constant for the

reaction, K. The effect of adding or removing

reactants, products, or heat on the equilibrium

concentrations can be predicted by Le

Châtelier’s principle.

After studying the material presented in this chapter, you should be able to: 1. define the thermodynamic system, surroundings, and universe (Section 9.1); 2. state the first law of thermodynamics (Section 9.1); 3. determine

ΔE from q and w (Section 9.1);

4. define enthalpy (Section 9.2); 5. define combustion and explai

n the importance of combustion reactions (Section 9.3);

6. use bond dissociation energies to approx

imate enthalpies of reaction (Section 9.4);

7. define entropy (Section 9.5); 8. predict the importance and the sign of

ΔS for a chemical reaction (Section 9.5);

9. state the second law of thermodynamics (Section 9.6); 10.

define Gibbs free energy (Section 9.7);

11.

determine spontaneity from the sign of

ΔG (Section 9.7);

12.

determine the extent of

reaction from the sign of

ΔG

o (Section 9.8);

13.

discuss how the extent of reaction varies with T (Section 9.8);

14.

sketch a reaction energy diagram showing the activation energies for the forward and reverse reactions (Section 9.9);

15.

write the rate law for a simple collision process (Section 9.10);

16.

describe and define chemical equilibrium from

the viewpoint of kinetics (Section 9.11);

17.

predict

relative

rate constants and extents of reaction from reaction energy diagrams

(Section 9.11);

18.

explain the meaning of single versus double

arrows in a chemical equation (Section 9.11);

19.

write the equilibrium constant expressi

on for a chemical equation (Sections 9.11);

20.

predict the temperature dependence of

ΔG

o and K (Sections 9.8 and 9.11); and

21.

predict the impact of a stress

on an equilibrium (Section 9.12).

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