Drill: Calculate the osmotic

pressure of 5.0 g NaOH in 7500

mL soln at 27oC.

Drill: Calculate the heat change when 25.0 g of H2O goes from 66.3oC

to 26.3oC.Cwater = 4.18 J/gK

Chemical Kinetics or

Reaction Rates

Reaction Rate•The speed at which reactants become products in a chemical reaction

•M/s = mole/Ls

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

• Collisions (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

Drill:List & describe at least 5 factors that will affect reaction

rates

Rate Expression•An equation showing how rate depends on the number 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:

H2(g) + N2(g) NH3(g)

Rate = k(PH2)3(PN2)

Write Rate Expressions for:

2HCl(aq) + 1Ba(OH)2(aq)

1BaCl2(aq) + 2H2O (l)

Rate =

k[HCl]2[Ba(OH)2]

Write Rate Expressions for:

1 Cl2(g) + 1 HOOH (aq)

2 HOCl(aq)

Write Rate Expressions for:

1 Cl2(g) + 1 HOOH (aq)

2 HOCl(aq)

Rate = k(PCl2) or

Rate = k[HOOH]

Write the Rate Law for:

2A(aq) + B(aq) + 3C(s)

Products

Write the Rate Law for:

2A(aq)+ B(aq)+ 3C(s) P

Rate = k[A]2[B]

Reaction Order•The total number of reactants (coefficients)

•Equals total exponents in rate expression

Drill: Write the rate expression & determine

rxn order for:

SO2(g) + O2 (g)

SO3(g)

Drill: Write the rate expression & determine rxn order for:

2 SO2(g) + 1 O2 (g)

2 SO3(g)

Rate = k(PSO2)2(PO2)

Determining Rxn Order

• Find rate expression ratios

• (Ratio of concentrations)x = rate ratio

• x = exponent

Write the rate expression for:

aA + bB

Products

All aqueous

The next slide includes data from an experiment where various concentrations of A & B were added together, and the rates of product

formation was measured.

Experimental ResultsExp [A] [B] Rate

1 1.0 1.0 2

2 2.0 1.0 4

3 1.0 2.0 8

Experimental ResultsExp [A] [B] Rate

1 1.0 1.0 2

2 2.0 1.0 4

3 1.0 2.0 8

Write the rate expression for:

aA + bB + cC

Products

All aqueous

Experimental ResultsExp # [A] [B] [C] Rate

1 0.1 0.1 0.1 3

2 0.3 0.1 0.1 81

3 0.1 0.3 0.1 27

4 0.1 0.1 0.3 3

Experimental ResultsExp # [A] [B] [C] Rate

1 0.1 0.1 0.1 3

2 0.3 0.1 0.1 81

3 0.1 0.3 0.1 27

4 0.1 0.1 0.3 3

Solve All: Exp Data:Exp # [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

Solve All: Exp Data:Exp # [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

Drill: Solve AllExp Data:

Exp # [R] [S] Rate

1) 0.25 0.20 2

2) 0.25 0.60 18

3) 0.50 0.20 4

Solve All: Exp Data:

Exp # [R] [S] Rate

1) 0.25 0.20 2

2) 0.25 0.60 18

3) 0.50 0.20 4

Solving exponents with a calculator.

Ax = B

Ax = B

Log Ax = log B

xLog A = log B

Thus:

x =Log BLog A

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:

Drill:List & describe at least 5 factors that will affect reaction

rates

Half-Life•The time required for one half of the reactants to change into products

in a reaction

Useful RelationshipsRxn Order Rate Exp

0 Rate = k

1 Rate = k[A]

2 Rate = k[A]2

1st Order Age Dating Formula t = ln(Ai/Af)t1/2

0.693

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 All: Exp DataExp # 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

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160

Time (s)

Tem

per

atu

re (

C)

Solving Rxn ExponentRate2 k [IO3

-]x[S2O5-2]y

Rate2 k [IO3-]x[S2O5

-2]y

M/31 s k(0.10M)x(0.10M)y

M/66 s k(0.10M)x(0.05M)y

=

=

Plot of Absorbance vs Wavelength

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

400 450 500 550 600 650 700

Wavelength (nm)

Ab

sorb

ance

[Z]Abs 640

0.1 0.66

0.075 0.495

0.05 0.33

0.025 0.165

0.01 0.066

Plot of Abs vs Concentration

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.02 0.04 0.06 0.08 0.1 0.12

Concentration (M)

Ab

sorb

ance

Drill: Solve Rate Expr:

X + Y M + N fast

3M + N 2G fast

2N K fast

2G + K Prod. slow

Rate Law & Net RxnA + B C + D fast

4C + A 2G fast

4D + B 2K fast

G + K Q + W slow

Q + 2 W Prod. fast

Review

Drill: Determine AllExp # T [A] [B] Rate

1) 27oC 0.10 0.10 2

2) 27oC 0.30 0.10 54

3) 27oC 0.10 0.20 8

4) 77oC 0.10 0.10 200

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