Chemical Kinetics or Reaction Rates

You have 6 ball bearings with identical magnetic strength but different diameters where A > B > C > D > E > K. Which two will hold together the most & the least.

Reaction Rate The speed at which reactants become products in a chemical reaction M/s

Kinetic Theory All matter is made up of tiny particles The particles are in constant motion All collisions are elastic ?

Elastic Collisions Collisions in which there is no energy change

Particles Reacting For particles to react, they must collide Reaction rate is dependent on collision rate

Particles Reacting When a reaction takes place, an energy change occurs Collision in which reactions occur are not elastic

Reaction Rate Rate = - d[Reactant]/dt Rate = +d[Product]/dt M/s

Factors Affecting Rxn Rate Concentration, Temperature, Agitation, Process, Orientation, Catalyst, SA of Solid, Pressure of Gas, Reaction Mechanism

List & describe all of the factors affecting rxn rates.

Drill: List at least 5 factors that will affect reaction rates

Rate Expression An equation showing how rate depends on the amount of reactants in a rate determining reaction

Rate Expression Rxn: aA (aq) + bB (aq) P Expr: Rate = k[A] a [B] b [A] = molarity of A

Rate Expression Rxn: aA (g) + bB (g) Product Exp: Rate = kP A a P B b

Write Rate Expressions for: H 2(g) + N 2(g) NH 3(g) HCl (aq) + Ba(OH) 2(aq) BaCl 2(aq) + H 2 O (l)

Write Rate Expressions for: Cl 2(g) + HOOH (aq) P (aq)

Reaction Order The total number of reactants Equals total of all of the coeffecients of R in the rxn Equals total exponents in rate expression

Determining Rxn Rate Find rate expression ratios (Ratio of concentrations) x = rate ratio x = exponent

Experimental Results Exp [A] [B] [C] Rate

Experimental Results Exp # [A] [B] [C] Rate

Half-Life The time required for one half of a reactant to be decomposed in a reaction

Useful Relationships Rxn OrderRate Exp 0 R=k 1 R=k[A] 2 R=k[A] 2

Useful Relationships Rxn OrderHalf Life 0 [A o ]/2k /k 2 1/k[A]

Useful Relationships Rxn OrderLin Plot 0[A] vs k 1 ln[A] vs k 2 1/[A] vs k

Useful Relationships Rxn OrderCalc R E 0 -d[A]/dt = k 1 -d[A]/dt = k[A] 2 -d[A]/dt = k[A] 2

Experimental Results Exp # [R] [S] [T] Rate 1) ) ) )

Clausius-Claperon Eq E a = R ln (T 2 )(T 1 ) k 2 (T 2 – T 1 ) k 1

Calculate the activation energy of a reaction whose rate constant is 2.0 x 10 3 at 27 o C and is 2.0 x 10 6 at 77 o C:

Experimental Results Exp # T [A] [B] Rate 1) 27 o C ) 27 o C ) 27 o C ) 77 o C

Reaction Mechanism The sequence of steps that make up the reaction process

Reaction Mechanism Step 1A Bfast Step 2B ---> Cslow Step 3C Dfast Total A ---> D

Reaction Mechanism The rate determining step in a reaction mechanism is the slowest step

Reaction Mechanism To solve the rate expression, you must use the slowest step

Solve Rate Expression A + B C + D fast 2C + A G fast 2D + B K fast 2G + 2K Prod. slow

Solve Rate Expression X + Y M + N fast M + N 2G slow 2N + G K fast 2G + 2K Prod. fast

Solve Rate Expression X + Y M + N fast 3M + N 2G fast 2N K fast 4G + 2K Prod. slow

Solve Rate Expression A + B C + Dfast 4C + A 2Gfast 4D + B 2Kfast G + K Q + Wslow Q + WProd.fast

Review

Experimental Results Exp # T [A] [B] Rate 1) 27 o C ) 27 o C ) 27 o C ) 77 o C

Solve Rate Expression A + B C + Dfast 4 C + A 2Gfast 2 K 4D + B fast G + K Q + Wfast 2Q + 2W Prod.slow