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Reaction Rates and Stoichiometry PowerPoint Presentation

Reaction Rates and Stoichiometry

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Reaction Rates and Stoichiometry

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-[C4H9Cl]

t

Rate =

=

[C4H9OH]

t

C4H9Cl(aq) + H2O(l) C4H9OH(aq) + HCl(aq)

- 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 ofC4H9OH.

1

2

[HI]

t

Rate = −

=

[I2]

t

What if the ratio is not 1:1?

2 HI(g) H2(g) + I2(g)

aA + bB

cC + dD

= −

=

=

Rate = −

1

b

1

a

1

c

1

d

[D]

t

[C]

t

[A]

t

[B]

t

- To generalize, then, for the reaction

Sample Exercise 14.3 p. 563

One can gain information about the rate of a reaction by seeing how the rate changes with changes in concentration.

N2(g) + 2 H2O(l)

NH4+(aq) + NO2−(aq)

If we compare Experiments 1 and 2, we see that when [NH4+] doubles, the initial rate doubles.

N2(g) + 2 H2O(l)

NH4+(aq) + NO2−(aq)

Likewise, when we compare Experiments 5 and 6, we see that when [NO2−] doubles, the initial rate doubles.

aA + bB

products

- This means theRate [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,
andkis the rate constant.

mandnare calledreaction orders.

Therefore,

- Exponents indicate how the rate is affected by each reactant concentration – termed reaction orders.
- Rate Law must be determined experimentally.

Rate = 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.

- Reveals how fast or slow rxn proceeds.
- LARGE k (~ 109 ) = FAST
- small k (< or = 10 ) = SLOW

- Homework Chemical Kinetics: Rate Laws WS