# Chapter 10 Self Test

## Finding the Mechanism

The following data were obtained for the oxidation of CO over a catalyst. All rates are initial rates

 .020 0.01 1 .035 0.01 3 .049 .01 6 .060 .01 9 .196 .1 1 .384 .2 1 .902 .5 1 1.653 1 1 4.44 5 1 5.00 10 1 4.44 20 1 2.77 50 1

The initial rate was found to be independent of CO2.

a)   Suggest a rate law consistent with the data

Hint 1  Sketch versus CO2.

Hint 2  Sketch versus CCO at low concentration.

Hint 3  Sketch versus CCO at high concentration.

Full Solution What is the rate law?

b)   Suggest mechanisms consistent with the rate law

Hint 1 What do the trends suggest?

Hint 2 What is the mechanism?

## Hint 1

Use only the data points for which the concentration of CO is the same.

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## Hint 2: Low concentration

For constant CO2

We see at low concentration the rate is linear in CO and

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## Hint 3: High concentration

At high concentrations the rate decreases with increasing concentration

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## Full Solution: Part A

Combining

For fixed concentration of O2 and low concentration of CO and

High concentration

Consequently the rate law

Satisfies the data

Back to Part b

## Hint 1

From the denominator of the rate law, we see that CO is adsorbed and that O2 is either weakly adsorbed (KO2PO21/2 << 1) or not adsorbed at all.

The 1/2 order with respect to oxygen suggests dissociative adsorption.

Because the initial rate is independent of CO2, it is either not adsorbed on the surface or weakly adsorbed.

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## Hint 2

The following mechanism is consistent with the rate law

Surface Reaction

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## Full Solution: Part B

The following mechanism is consistent with the rate law

Surface Reaction

Assume surface reaction limits

1)

2)

3)

4)

5)

We see that oxygen is weakly adsorbed (very small) such that

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