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
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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
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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