University:
York University
Course:
CHEM 1001 | Chemical Dynamics
Academic year:

2022
Views:

112

Pages:

3
Author:

Niklas

03/30/2022 Chapter 15 04/01/2022 04/04/2022 •Determining the rate law •Differential rate law: rate==[A] •Integrated rate law: [A]: [A]ekt; In[A]: In[A]o-kt graphical analysis -plot of In[A] vs. t first onder Slope:-k • intercept = In [A] • In of plot of [A]: [A] e** - plot of skt-cag = second order reaction Slope: k • intercept: - plot of [A]=-kt+[A]: zero order reaction • Slope -k • intercapt = CAD Half Lifetime it takes for concentration of reactant to drop to half its initial value -1st order reactions • independent of concentration 0.643 -constant half life implies first-order reaction Akt -Inta -kt -2nd order reactions -half life depends on [A]。 •# of transition states = # of steps in reaction Beaction Coordinate Diagram Transition Transition state Transition stale Product tranution state Intermediate Energr Intermediate Intermediate Reactant 04/04/2022 Chapter 15 •breaking of bonds/steps of formation -Ex. 2H2+O2→ 2H20 DH-HHH 2) H+0=0H-٥٠ HO-OH٤( ١-٥-٥ 0-0 4) H-O-OHH-OO-H 5) H HOHOH Η 6) H-HO H • first step is the one that determines the reaction in this example •Chemical reaction mechanisms -reaction mechanism molecular-level process by which a reaction occurs - elementary reaction Steps •rate law exponents are the stoichiomakic coefficients -most reactions do not occur in a single step but instead in multiple elementary reactions multi-step mechanisms - intermediate a molecule that is procluced in the reaction but doesn't appear in the overalا Stoichiometry •typically higher in energy than the products. •cletection of intermediates is important for confirming proposed mechanisms Multi-step example: NO, +CC NO+CO, Mechanism: NO₂+ NO NO + NO NOCO NO CO NOCO NO CO (1) (2) overall -rate law depends on the slowest stop •if step 1 is slow, then rate = k, [No,]" if step 2 is slow, then raterk, [No] [CO] •compare with experiment to figure out which is correct • intermediates don't appear in rate law •step with the highest activation energy = rale determining step 04/04/2022 Chapter 15 04/06/2022 Reaction Coordinate Diagram with Intermediates - equilibrium develops at low temperatures determining rate law 1) measure experimental rate law 2) postulate the elementary Steps 3) determine the rate law implied by the proposed mechanism & compare it with the experimental rate law •Seroral possible mechanisms can fit an observed rate law. Determining the rate a 3 body collisions are highly unlikely -unless in Solvent only 1 or 2 molecules collide at 1 time Temperature dependence of reaction rates -as temp increases, reaction rate increases •reactants must collide with enough energy for the reaction to occur For a reaction to occur: - collision concentration dependence in rate laws -sufficient kinetic energy to overcome activation energy relates to temperature -Correct orientation for the molecules to react