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Ch.14 - Chemical Kinetics
All textbooksBrown 14th EditionCh.14 - Chemical KineticsProblem 78
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Chapter 14, Problem 78

In solution, chemical species as simple as H+ and OH- can serve as catalysts for reactions. Imagine you could measure the [H+] of a solution containing an acid-catalyzed reaction as it occurs. Assume the reactants and products themselves are neither acids nor bases. Sketch the [H+] concentration profile you would measure as a function of time for the reaction, assuming t = 0 is when you add a drop of acid to the reaction.

Verified step by step guidance
1
Step 1: Understand that the addition of an acid to the reaction at t = 0 will increase the concentration of hydrogen ions, [H+], in the solution.
Step 2: Recognize that as the acid-catalyzed reaction proceeds, the [H+] may initially remain relatively constant if the acid is in excess and the reaction is slow compared to the rate of acid consumption.
Step 3: Consider that as the reaction progresses, the [H+] may start to decrease if the acid is consumed faster than it is replenished, or if the reaction reaches completion.
Step 4: Sketch a graph with time on the x-axis and [H+] on the y-axis, starting with a high [H+] at t = 0, then showing a plateau if the acid is in excess, followed by a potential decrease as the reaction consumes the acid.
Step 5: Label the graph to indicate the initial increase in [H+], the plateau phase, and any decrease in [H+] as the reaction proceeds and the acid is consumed.
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Related Practice
Textbook Question

You have studied the gas-phase oxidation of HBr by O2: 4 HBr(g) + O2(g) → 2 H2O(g) + 2 Br2(g)

You find the reaction to be first order with respect to HBr and first order with respect to O2. You propose the following mechanism:

HBr(g) + O2(g) → HOOBr(g)

HOOBr(g) + HBr(g) → 2 HOBr(g)

HOBr(g) + HBr(g) → H2O(g) + Br2(g)

(b) Based on the experimentally determined rate law, which step is rate determining?

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Textbook Question

(c) Do catalysts affect the overall enthalpy change for a reaction, the activation energy, or both?

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Textbook Question

(a) Most commercial heterogeneous catalysts are extremely finely divided solid materials. Why is particle size important?

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Open Question
The oxidation of SO2 to SO3 is accelerated by NO2. The reaction proceeds according to: NO2(g) + SO2(g) → NO(g) + SO3(g) 2 NO(g) + O2(g) → 2 NO2(g) (a) Show that, with appropriate coefficients, the two reactions can be summed to give the overall oxidation of SO2 by O2 to give SO3. (d) Is this an example of homogeneous catalysis or heterogeneous catalysis?
Textbook Question

The addition of NO accelerates the decomposition of N2O, possibly by the following mechanism: NO1g2 + N2O1g2¡N21g2 + NO21g2 2 NO21g2¡2 NO1g2 + O21g2 (b) Is NO serving as a catalyst or an intermediate in this reaction?

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Textbook Question

Many metallic catalysts, particularly the precious-metal ones, are often deposited as very thin films on a substance of high surface area per unit mass, such as alumina 1Al2O32 or silica 1SiO22. (b) How does the surface area affect the rate of reaction?

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