Chapter16:

  However, there are still questions that we need to answer…   How fast will the reaction take?   Will the reactants react to completion?   Will the reaction proceed by itself and release

energy? or does it need an input of energy to drive it forward?

  How fast will the reaction proceed?   It is the study of reaction rates.   REACTION RATES is the change in the

concentration of a reactant or product with time (M/s) AB

time

  Concentration of reactants

  Temperature

  Physical State: Surface Area

  Catalysis

Concentration Rateofreaction

Temperature

Surfaceareaofsolidorliquid

Presenceofcatalyst(light,compounds)

Rateofreaction

Rateofreaction

Rateofreaction

€

Rate of reaction =change in concentration of A

change in time

Rate of reaction =A[ ]2 − A[ ]1

t2 − t1= −

Δ A[ ]Δt

€

Rate of reaction =change in concentration of A

change in time

Rate of reaction =A[ ]2 − A[ ]1

t2 − t1= −

Δ A[ ]Δt

€

Rate of reaction =change in concentration of B

change in time

Rate of reaction =B[ ]2 − B[ ]1

t2 − t1=Δ B[ ]Δt

C2H4 (g) + O3 (g) C2H4O (g) + O2 (g)

  Rate between specific intervals

  t=0.0 and t=30.0   t=10.0 and t=60.0   t=0.0 and t=50.0

  Rateataspecifictime

  Δt0  Slopeofthelinetangenttothepoint

Br2(aq)+HCOOH(aq)2Br‐(aq)+2H+(aq)+CO2(g)

averagerate=‐Δ[Br2]Δt

=‐[Br2]final–[Br2]initial

tfinal‐tinitial

slopeoftangent

slopeoftangent slopeof

tangent

instantaneousrate=rateataspecifictime

  Initial Rate is the instantaneous rate at the beginning of the reaction

  This is usually measured to avoid complications as the reaction proceeds.

  Two moles of HI disappears for every mole of H2 and I2 that appears

2HIH2+I2

  In general aA+bBcC+dD

rate=‐Δ[A]Δt

1a

=‐Δ[B]Δt

1b

=Δ[C]Δt

1c

=Δ[D]Δt

1d

Write the rate expression for the following reaction:

CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)

  Spectrometric Formation of colored products

  Conductometric Formation of charged species

NO(g) + O3(g) O2(g) + NO2 (g) colorless colorless colorless brown

(CH3)3C-Br(l) + H2O(l) (CH3)3C-OH (l) + H+(aq) +Br –(aq)

  Manometric Formation of gases

  Direct Chemical formation of reactive species (can be further reacted via titration, gravimmetry, etc.)

Zn(s)+ 2 CH3COOH(aq) Zn2+(aq) + 2 CH3COO– (aq) + H2(g)

> 2x > 2x4x 4x

> 2x > 2x4x 4x

For the reaction,

•  With [NO2-], Rate α [NH4

+] •  With [NH4

+], Rate α [NO2-],

Rate α [NH4+][NO2

-] Rate = k[NH4

+][NO2-]

  Or Rate Equation expresses the rate as a function of reactant concentrations, product concentrations and temperature…

  The order of the reaction tells you by how much rate changes as you change a particular concentration

€

Rate = k A[ ]m B[ ]n

  Can be zero, first, second, etc.   Can be fractions   Can be negative

Experiment Initial Reactant Concentration (M)

Initial Rate (M/s)

O2 NO 1 1.10 x 10–2 1.30 x 10–2 3.21 x 10–3

2 2.20 x 10–2 1.30 x 10–2 6.40 x 10–3 3 1.10 x 10–2 2.60 x 10–2 12.8 x 10–3 4 3.30 x 10–2 1.30 x 10–2 9.60 x 10–3 5 1.10 x 10–2 3.90 x 10–2 28.8 x 10–3

Experiment Initial Reactant Concentration (M)

Initial Rate (M/s)

NO2 CO 1 0.10 0.10 0.0050

2 0.40 0.10 0.080 3 0.10 0.20 0.0050

F2(g)+2ClO2(g)2FClO2(g)

  Rate laws are always determined experimentally

  Reaction order shows how the reaction depends on reactant concentration

  Reaction order is always defined in terms of reactant (not product) concentrations

  The order is not related to stoichiometric coefficient

F2(g)+2ClO2(g)2FClO2(g)

rate=k[F2][ClO2]1

  January 14, 2009, Wednesday   6:00-8:00 PM   SEC A 210/214/215

  Bring 2 blue books   Calculator

  3, 4, 5, 11, 12, 13, 17, 18, 22, 23 – Due Wed January 21

  32, 34, 35, 37, 39, 41, 42, 43, 48, 49, 76, 79 – Due Mon, January 26

  83, 87, 93, 97, 99, 104, 119 – Due Friday, January 30