chemical kinetics or reaction rates
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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 = kPAaPB
b
Write Rate Expressions for:
H2(g) + N2(g) NH3(g)
HCl(aq) + Ba(OH)2(aq)
BaCl2(aq) + H2O (l)
Write Rate Expressions for:
Cl2(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 ResultsExp [A] [B] [C] Rate
1 1.0 1.0 1.0 2
2 2.0 1.0 1.0 4
3 1.0 2.0 1.0 8
4 1.0 1.0 2.0 4
Experimental ResultsExp # [A] [B] [C] Rate
1 0.1 0.1 0.1 3
2 0.3 0.1 0.1 9
3 0.1 0.3 0.1 27
4 0.1 0.1 0.3 3
Half-Life•The time required for one half of a reactant
to be decomposed in a reaction
Useful RelationshipsRxn Order Rate Exp
0 R=k
1 R=k[A]
2 R=k[A]2
Useful RelationshipsRxn Order Half Life
0 [Ao]/2k
1 0.693/k
2 1/k[A]
Useful RelationshipsRxn Order Lin Plot
0 [A] vs k
1 ln[A] vs k
2 1/[A] vs k
Useful Relationships• Rxn Order Calc R E
• 0 -d[A]/dt = k
• 1 -d[A]/dt = k[A]
• 2 -d[A]/dt = k[A]2
Experimental ResultsExp # [R] [S] [T] Rate
1) 0.25 0.20 0.10 2
2) 0.25 0.60 0.10 18
3) 0.50 0.20 0.10 4
4) 0.25 0.20 0.40 32
Clausius-Claperon Eq
Ea= R ln(T2)(T1) k2
(T2 – T1) k1
Calculate the activation energy of a reaction
whose rate constant is 2.0 x 103 at 27oC and is
2.0 x 106 at 77oC:
Experimental ResultsExp # T [A] [B] Rate
1) 27oC 0.10 0.10 2
2) 27oC 0.30 0.10 18
3) 27oC 0.10 0.20 4
4) 77oC 0.10 0.10 20
Reaction Mechanism
•The sequence of steps that make up
the reaction process
Reaction Mechanism
Step 1 A <--> B fast
Step 2 B ---> C slow
Step 3 C <--> D fast
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 ExpressionA + B C + D fast
4C + A 2G fast
4D + B 2K fast
G + K Q + W slow
Q + W Prod. fast
Review
Experimental ResultsExp # T [A] [B] Rate
1) 27oC 0.10 0.10 2
2) 27oC 0.30 0.10 18
3) 27oC 0.10 0.20 8
4) 77oC 0.10 0.10 20
Solve Rate ExpressionA + B C + D fast
4 C + A 2G fast
2 K 4D + B fast
G + K Q + W fast
2Q + 2W Prod. slow