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Ch.14 - Chemical Kinetics
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
All textbooksBrown 15th EditionCh.14 - Chemical KineticsProblem 112f
Chapter 14, Problem 112f

In a hydrocarbon solution, the gold compound (CH3)3AuPH3 decomposes into ethane (C2H6) and a different gold compound, (CH3)AuPH3. The following mechanism has been proposed for the decomposition of (CH3)3AuPH3:
Step 1: (CH3)3AuPH3 k1⇌k-1 (CH3)3Au + PH3 (fast)
Step 2: (CH3)3Au k2→ C2H6 + (CH3)Au (slow)
Step 3: (CH3)Au + PH3 k3→ (CH3)AuPH3 (fast)
(f) What would be the effect on the reaction rate of adding PH3 to the solution of (CH3)3AuPH3?

Verified step by step guidance
1
Identify the rate-determining step in the mechanism, which is the slowest step. In this case, it is Step 2: (CH_3)_3Au -> C_2H_6 + (CH_3)Au.
Recognize that the rate of the overall reaction is determined by the rate of the slowest step, Step 2.
Consider the role of PH_3 in the mechanism. PH_3 is involved in Step 1 and Step 3, both of which are fast steps.
Understand that since PH_3 is not involved in the rate-determining step (Step 2), adding more PH_3 will not affect the rate of the slow step.
Conclude that adding PH_3 to the solution will not change the overall reaction rate, as it does not influence the rate-determining step.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reaction Mechanism

A reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. Understanding the individual steps, including their rates and intermediates, is crucial for predicting how changes in conditions, such as concentration, will affect the overall reaction rate.
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Reaction Mechanism Overview

Rate Law

The rate law expresses the relationship between the rate of a chemical reaction and the concentration of its reactants. It is determined by the slowest step in the reaction mechanism, which dictates how the reaction rate changes with varying concentrations of reactants, such as the effect of adding PH<sub>3</sub> in this case.
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Rate Law Fundamentals

Catalysis and Inhibition

Catalysis involves the acceleration of a chemical reaction by a substance (catalyst) that is not consumed in the reaction. Conversely, the addition of certain substances can inhibit the reaction rate. Understanding how PH<sub>3</sub> interacts with the reactants can clarify whether it acts as a catalyst or an inhibitor in the decomposition of (CH<sub>3</sub>)<sub>3</sub>AuPH<sub>3</sub>.
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Related Practice
Textbook Question

One of the many remarkable enzymes in the human body is carbonic anhydrase, which catalyzes the interconversion of carbon dioxide and water with bicarbonate ion and protons. If it were not for this enzyme, the body could not rid itself rapidly enough of the CO2 accumulated by cell metabolism. The enzyme catalyzes the dehydration (release to air) of up to 107 CO2 molecules per second. Which components of this description correspond to the terms enzyme, substrate, and turnover number?

Textbook Question

Platinum nanoparticles of diameter 2 nm are important catalysts in carbon monoxide oxidation to carbon dioxide. Platinum crystallizes in a face-centered cubic arrangement with an edge length of 3.924 Å. (c) Using your results from (a) and (b), calculate the percentage of Pt atoms that are on the surface of a 2.0-nm nanoparticle. (d) Repeat these calculations for a 5.0-nm platinum nanoparticle.

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Textbook Question

In a hydrocarbon solution, the gold compound (CH3)3AuPH3 decomposes into ethane (C2H6) and a different gold compound, (CH3)AuPH3. The following mechanism has been proposed for the decomposition of (CH3)3AuPH3:

Step 1: (CH3)3AuPH3 k1⇌k-1 (CH3)3Au + PH3 (fast)

Step 2: (CH3)3Au k2→ C2H6 + (CH3)Au (slow)

Step 3: (CH3)Au + PH3 k3→ (CH3)AuPH3 (fast)

(c) What is the molecularity of each of the elementary steps?

Textbook Question

Platinum nanoparticles of diameter 2 nm are important catalysts in carbon monoxide oxidation to carbon dioxide. Platinum crystallizes in a face-centered cubic arrangement with an edge length of 3.924 Å. (b) Estimate how many platinum atoms are on the surface of a 2.0-nm Pt sphere, using the surface area of a sphere (4πr2) and assuming that the 'footprint' of one Pt atom can be estimated from its atomic diameter of 2.8 A .

Textbook Question

In a hydrocarbon solution, the gold compound (CH3)3AuPH3 decomposes into ethane (C2H6) and a different gold compound, (CH3)AuPH3. The following mechanism has been proposed for the decomposition of (CH3)3AuPH3:

Step 1: (CH3)3AuPH3 k1⇌k-1 (CH3)3Au + PH3 (fast)

Step 2: (CH3)3Au k2→ C2H6 + (CH3)Au (slow)

Step 3: (CH3)Au + PH3 k3→ (CH3)AuPH3 (fast)

(a) What is the overall reaction?

(b) What are the intermediates in the mechanism?

Textbook Question

In a hydrocarbon solution, the gold compound (CH3)3AuPH3 decomposes into ethane (C2H6) and a different gold compound, (CH3)AuPH3. The following mechanism has been proposed for the decomposition of (CH3)3AuPH3:

Step 1: (CH3)3AuPH3 k1⇌k-1 (CH3)3Au + PH3 (fast)

Step 2: (CH3)3Au k2→ C2H6 + (CH3)Au (slow)

Step 3: (CH3)Au + PH3 k3→ (CH3)AuPH3 (fast)

(e) What is the rate law predicted by this mechanism?