Chemical Kinetics Chapter 14

TRANSITION STATE

Activated Complex

Kinetics vs Thermodynamics

Catalysts

Collision Theory Particles must collide before they can react The collision must be properly oriented for the necessary arrangement of atoms and electrons Forceful enough – possessing enough energy to form products

Collision Theory Particles must collide before they can react The collision must be properly oriented for the necessary arrangement of atoms and electrons Forceful enough – possessing enough energy to form products

Rates of Reactions Reaction rates tell how fast reactants change into products Nature of reactants Concentration Temperature Surface Area Presence of a Catalyst

Elementary Steps Step 1: X + Y  M (slow) Step 2: X + M  Z (fast) What is the rate determining step? What are the intermediates? Is there a catalyst present? What is the net reaction?

Elementary Steps Step 1: 2NO  N2O2 Step 2: N2O2 + H2  N2O + H2O (slow) Step 3: N2O + H2  N2 + H2O What is the rate determining step? What are the intermediates? Is there a catalyst present? What is the net reaction?

Elementary Steps Step 1: Ce4+ + Mn2+  Ce3+ + Mn3+ Step 3: Tl+ + Mn4+  Tl3+ + Mn2+ What are the intermediates? Is there a catalyst present? What is the net reaction?

Rate Laws must be determined experimentally. Rate = k[A]x[B]y Rate Laws must be determined experimentally. The ONLY time you do NOT need to use the experimental trial is for a one step reaction.

Reaction Order xA(aq) + yB(aq)  AB(s) Rate = k[A]x[B]y It is order x with respect to A. It is order y with respect to B *The net reaction order = x + y.

What is the reaction order? Rate = k[A][B]2 What is the reaction order? Rate = k[A]3[B]2

Reaction Order Determine the rate law for the following one step reactions: 2NO + O2  2NO2 2NO + Br2  2NOBr

Determining Rate Laws Experimentally

Determining Rate Laws Experientially

Determining Rate Laws Experimentally Initial Rate Method: Rate1 [A]x1[B]y1 [A]1 x [B]1 y Rate2 [A]x2[B]y2 [A]2 [B]2