Textbook Question
Consider the two reactions:
O + N2 → NO + N Ea = 315 kJ/mol
Cl + H2 → HCl + H Ea = 23 kJ/mol
a. Why is the activation barrier for the first reaction so much higher than that for the second?
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Ch.15 - Chemical Kinetics
Chapter 15, Problem 111a
Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g) The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms. Proposed mechanism I: H2(g) + I2(g) → 2 HI(g) Single step Proposed mechanism II: I2(g) Δk1k-12 I(g) Fast H2( g) + 2 I( g) → k22 HI( g) Slow a. Show that both of the proposed mechanisms are valid.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reaction Order
Reaction order refers to the power to which the concentration of a reactant is raised in the rate law of a chemical reaction. In this case, the reaction is first order in both H2 and I2, meaning that the rate of reaction is directly proportional to the concentration of each reactant. Understanding reaction order is crucial for analyzing how changes in concentration affect the reaction rate.
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00:36
Average Bond Order
Mechanism of Reaction
A reaction mechanism is a step-by-step description of the pathway taken by reactants to form products. It includes elementary steps that detail how bonds are broken and formed. Evaluating proposed mechanisms involves determining if they can account for the observed reaction order and rate, which is essential for validating their correctness.
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03:06Reaction Mechanism Overview
Rate Law and Rate Constants
The rate law expresses the relationship between the rate of a chemical reaction and the concentration of its reactants, often incorporating rate constants for each step in a mechanism. For the proposed mechanisms, the rate constants (k1, k-1, k2) play a critical role in determining the overall rate of the reaction and validating the mechanisms based on the experimental data provided.
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00:45Rate Constant Units
Related Practice
Textbook Question
Consider the two reactions:
O + N2 → NO + N Ea = 315 kJ/mol
Cl + H2 → HCl + H Ea = 23 kJ/mol
b. The frequency factors for these two reactions are very close to each other in value. Assuming that they are the same, calculate the ratio of the reaction rate constants for these two reactions at 25 °C.
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Textbook Question
Anthropologists can estimate the age of a bone or other sample of organic matter by its carbon-14 content. The carbon-14 in a living organism is constant until the organism dies, after which carbon- 14 decays with first-order kinetics and a half-life of 5730 years. Suppose a bone from an ancient human contains 19.5% of the C-14 found in living organisms. How old is the bone?
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Textbook Question
Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g) The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms. Proposed mechanism I: H2(g) + I2(g) → 2 HI(g) Single step Proposed mechanism II: I2(g) Δk1k-12 I(g) Fast H2( g) + 2 I( g) → k22 HI( g) Slow b. What kind of experimental evidence might lead you to favor mechanism II over mechanism I?
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Textbook Question
Phosgene (Cl2CO), a poison gas used in World War I, is formed
by the reaction of Cl2 and CO. The proposed mechanism for the
reaction is:
Cl2Δ2 Cl (fast, equilibrium)
Cl + COΔClCO (fast, equilibrium)
ClCO + Cl2¡Cl2CO + Cl (slow)
Textbook Question
A certain substance X decomposes. Fifty percent of X remains after 100 minutes. How much X remains after 200 minutes if the reaction order with respect to X is (c) second order?
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