Outline:2/9/07 n n Physics Seminar – 3pm n n Exam 1 – one week from today… n Outline Finish Chapter 15 - Kinetics: - Arrhenius Rate equation & temperature dependence

  k = A e  E a /RT k = Rate law constant A = constant (frequency factor) E a = Arrhenius Activation Energy R = J/mol K T = Temperature n k also depends on temperature and Arrhenius Activation energy…. 15-6

What does Ea mean in terms of rate?   k = A e  E a /RT e.g. big E a  e  (big) = small k = small rate! e.g. small E a  e  (small) = big k = big rate!

The temperature dependence of a rate of reaction is used to determine the Activation Energy: Example: (eq on page ) Where does this come from? Algebra ….  Rate 2 = k 2 = A e  E a /RT 2  Rate 1 = k 1 = A e  E a /RT 1 divide these equations

Algebra ….  Rate 2 = k 2 = A e  E a /RT 2  Rate 1 = k 1 = A e  E a /RT 1 divide these equations

An example: The colorless gas N 2 O 2 decomposes to the brown gas NO 2 in a first-order reaction. The rate constant k = 4.5  10 3 s  at 274 K and 1.0  10 4 s  at 283 K. What is the activation energy E a ?  Use the correct equation: (eq. 15-8)  ln(k 2 /k 1 ) =  E a /R [1 /T 2  1/T 1 ]  ln(4.5/10) =  E a /8.315 [1 /283  1/274 ] E a = J = 57.2 kJ Example p. 651

How to study for this exam? Practice lots of examples….

Problems to try: Chapter 15 n 15.13, 15.17, 15.19, 15.21, 15.23, 15.25, 15.27, 15.29, 15.31, 15.33, 15.39, 15.45, 15.47, 15.51, 15.57, 15.59, 15.61, 15.63, 15.65, 15.67, 15.69, 15.73, 15.77, 15.81, 15.85, 15.87, 15.89, 15.91, 15.95,

Practice Problems: Chapter 14 n 14.11, 14.15, 14.17, 14.19, 14.23, 14.25, 14.27, 14.31, 14.35, 14.37, 14.38, 14.41, 14.43, 14.49, 14.51, 14.53, 14.55, 14.57, 14.61, 14.65, 14.67, 14.71, 14.75, 14.77, 14.79, 14.81, 14.91, ,

Problems to try: Chapter 13 n 13.1, 13.3, 13.5, 13.7, 13.9, 13.11, 13.15, 13.19, 13.21, 13.35, 13.43, 13.45, 13.47, Problems to try: Chapter 12 n 12.3, 12.5, 12.7, 12.9, 12.11, 12.17, 12.19, 12.29, 12.31, 12.33, 12.35, 12.39, 12.41, 12.43, 12.49, 12.51, 12.53, 12.55, 12.63

Activation Energy The rearrangement of methyl isonitrile: –The energy required for the above twist and break is the activation energy, E a. –Once the C-N bond is broken, the N  C portion can continue to rotate forming a C-C  N bond. What exactly is E a ?

The  E for the reaction is the difference in energy between CH 3 NC and CH 3 CN. The activation energy is the difference in energy between reactants, CH 3 NC and transition state. The rate of reaction depends on E a. k = A e  E a /RT Activation Energy

How can a catalyst affect the rate of reaction? It lowers the E a …. And E a appears in the exponent!!!  k = A e  Ea/RT

A catalyst lowers E a

DEMO: Catalytic Converters

change the rate of a chemical reaction there are two types of catalyst: –homogeneous (all in same phase) –heterogeneous (in different phases) typically lower the E a for a reactionCatalysts

Enzymes are biological catalysts. Most enzymes are proteins with large molar masses (10 4  10 6 amu). Enzymes have very specific shapes and catalyze very specific reactions. Another Example of Catalysis

Only substrates that fit into the enzyme lock can be involved in the reaction. If a molecule binds tightly to an enzyme so that another substrate cannot displace it, then the active site is blocked and the catalyst is inhibited (enzyme inhibitors). The number of events catalyzed (turnover number) is large for enzymes: 10 3  10 7 sec -1.Enzymes

Quiz #4 n Please put away your books and notes…. n When you are finished, you may turn it in to me and leave… Have a great Winter Break!