Chemistry Chapter 17

1. Chemistry Chapter 17 Reaction Energy and Reaction Kinetics

2. A Bomb Calorimeter

3. A Cheaper Calorimeter

4. Specific Heat The amount of heat required to raise the temperature of one gram of substance by one degree Celsius.

5. Table of Specific Heats

6. Calculations involving Specific Heat cp = ___q__ m x T q = cp x m x T OR cp = Specific Heat q = Heat lost or gained T = Temperature change

7. Heat of Reaction The amount of heat released or absorbed during a chemical reaction. Endothermic: Reactions in which energy is absorbed as the reaction proceeds. Exothermic: Reactions in which energy is released as the reaction proceeds.

8. Endothermic Reactions

9. Exothermic Reactions

10. Enthalpy and Entropy Reactions tend to proceed in the direction that lowers the energy of the system (H, enthalpy). Reactions tend to proceed in the direction that increases the disorder of the system (S, entropy).

11. Spontaneity of Reactions Reactions proceed spontaneously in the direction that lowers their free energy, G. G = H - TS If G is negative, the reaction is spontaneous. If G is positive, the reaction is NOT spontaneous.

12. Chemical Kinetics The area of chemistry that concerns reaction rates.

13. Collision Model Key Idea: Molecules must collide to react. However, only a small fraction of collisions produces a reaction. Why?

14. Collision Model • Collisions must have enough energy to produce the reaction (must equal or exceed the activation energy). • Orientation of reactants must allow formation of new bonds.

15. Factors Affecting Rate • Temperature • Increasing temperature always increases the rate of a reaction. • Surface Area • Increasing surface area increases the rate of a reaction • Concentration • Increasing concentration USUALLY increases the rate of a reaction • Presence of Catalysts

16. Catalysis • Catalyst: A substance that speeds up a reaction without being consumed • Enzyme: A large molecule (usually a protein) that catalyzes biological reactions. • Homogeneous catalyst: Present in the same phase as the reacting molecules. • Heterogeneous catalyst: Present in a different phase than the reacting molecules.

17. Catalysts Increase the Number of Effective Collisions

18. Endothermic Reaction witha Catalyst

19. Exothermic Reaction with a Catalyst

20. Heterogeneous Catalysis Steps: • 1. Adsorption and activation of the reactants. • 2. Migration of the adsorbed reactants on the surface. • 3. Reaction of the adsorbed substances. • 4. Escape, or desorption, of the products.

21. Rate Laws Rate =k[NO2]n • k = rate constant • n = rate order

22. Reaction Mechanism • The series of stepsby which a chemical • reaction occurs. • A chemical equation does not tell us • howreactants become products • It is asummaryof theoverallprocess. Example: has many steps in the reaction mechanism

23. Rate-Determining Step In a multi-step reaction, the slowest stepis the rate-determining step. It therefore determines the rate of reaction.