reaction rates and stoichiometry
DESCRIPTION
- [C 4 H 9 Cl] t. Rate =. =. [C 4 H 9 OH] t. Reaction Rates and Stoichiometry. C 4 H 9 Cl( aq ) + H 2 O( l ) C 4 H 9 OH ( aq ) + HCl( aq ). In this reaction, the ratio of C 4 H 9 Cl to C 4 H 9 OH is 1:1 . - PowerPoint PPT PresentationTRANSCRIPT
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Reaction Rates and Stoichiometry
• In this reaction, the ratio of C4H9Cl to C4H9OH is 1:1.
• Thus, the rate of disappearance of C4H9Cl is the same as the rate of appearance of C4H9OH.
C4H9Cl(aq) + H2O(l) C4H9OH(aq) + HCl(aq)
Rate = -[C4H9Cl]t
= [C4H9OH]t
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Reaction Rates and Stoichiometry
What if the ratio is not 1:1?
2 HI(g) H2(g) + I2(g)
Rate = − 12
[HI]t
= [I2]t
[H2]t
=
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Reaction Rates and Stoichiometry• To generalize, then, for the reaction
aA + bB cC + dD
Rate = −1a
[A]t = −
1b
[B]t =
1c
[C]t
1d
[D]t=
Sample Exercise 14.3 p. 563
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Concentration and RateOne can gain information about the rate of a reaction by seeing how the rate changes with changes in concentration.
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Sulfur Clock Demonstration Data
FLASK LABEL REACTION TIME (SECONDS)
A
B
C
D
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Concentration and Rate
If we compare Experiments 1 and 2, we see that when [NH4
+] doubles, the initial rate doubles.
NH4+(aq) + NO2
−(aq) N2(g) + 2 H2O(l)
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Concentration and Rate
Likewise, when we compare Experiments 5 and 6, we
see that when [NO2−] doubles, the initial rate doubles.
NH4+(aq) + NO2
−(aq) N2(g) + 2 H2O(l)
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What is Rate Law?
aA + bB products
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Concentration and Rate
• This means the Rate [NH4+] & Rate [NO2
−]
Rate [NH4+] [NO2
−]
which, when written as an equation, becomes
Rate Law Eqn = k [NH4+]m [NO2
−]n
• This equation is called the rate law, and k is the rate constant.
m and n are called reaction orders.
Therefore,
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What are m and n exponents?• Exponents indicate how the rate is affected by
each reactant concentration – termed reaction orders.
• Rate Law must be determined experimentally.
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Overall Reaction OrderRate = k [NH4
+]m [NO2−]n
• The overall reaction order can be found by adding the exponents on the reactants in the rate law … so m + n = ? 1 + 1 = 2
• This reaction is second-order overall.
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Rate Constant (k)• Reveals how fast or
slow rxn proceeds.
• LARGE k (~ 109 ) = FAST RATE
• small k ( < or = 101 ) = SLOW RATE
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Sample Exercise 14.6 p.568
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Sample Exercise 14.6 p.568
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Sample Exercise 14.6 p.568
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HOMEWORK INVOLVES PRACTICE