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Ch.14 - Chemical Kinetics
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 15th EditionCh.14 - Chemical KineticsProblema 13
Capitolo 14, Problema 13

Based on the following reaction profile, how many intermediates are formed in the reaction A⟶C? How many transition states are there? Which step, A⟶B or B⟶C, is the faster? For the reaction A⟶C, is Δ𝐸 positive, negative, or zero? [Section 14.5]

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insert step 1> Identify the number of peaks and valleys in the reaction profile. Each peak represents a transition state, and each valley represents an intermediate.
insert step 2> Count the number of valleys to determine the number of intermediates formed in the reaction A⟶C.
insert step 3> Count the number of peaks to determine the number of transition states in the reaction A⟶C.
insert step 4> Compare the activation energies of the steps A⟶B and B⟶C. The step with the lower activation energy is the faster step.
insert step 5> Determine the overall change in energy (Δ𝐸) for the reaction A⟶C by comparing the energy of the reactants (A) and the products (C). If the energy of C is lower than A, Δ𝐸 is negative; if higher, Δ𝐸 is positive; if the same, Δ𝐸 is zero.

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Reaction Profile

A reaction profile is a graphical representation of the energy changes that occur during a chemical reaction. It typically shows the energy of reactants, products, intermediates, and transition states as the reaction progresses. Understanding the profile helps identify the energy barriers and the overall energy change (ΔE) of the reaction, which is crucial for determining the number of intermediates and transition states.
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Intermediates and Transition States

Intermediates are species that are formed during the reaction but are not present in the final products; they exist at local energy minima on the reaction profile. Transition states, on the other hand, are high-energy states that occur at the peaks of the energy profile, representing the point of maximum energy along the reaction pathway. The number of each can be determined by analyzing the reaction profile.
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Activation Energy and Reaction Rate

Activation energy is the minimum energy required for a reaction to occur, influencing the rate of the reaction. The step with the lower activation energy is typically the faster step. By comparing the energy barriers of the steps A⟶B and B⟶C on the reaction profile, one can determine which step is faster and infer the sign of ΔE based on the overall energy difference between reactants and products.
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Domanda del libro di testo

The following graph shows two different reaction pathways for the same overall reaction at the same temperature. Is each of the following statements true or false? (b) For both paths, the rate of the reverse reaction is slower than the rate of the forward reaction.

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(b) Name three factors that can affect the rate of a chemical reaction.

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The accompanying graph shows plots of ln k versus 1/𝑇 for two different reactions. The plots have been extrapolated to the y-intercepts. Which reaction (red or blue) has b. the larger value for the frequency factor, A? [Section 14.4]

Domanda del libro di testo

Consider the diagram that follows, which represents two steps in an overall reaction. The red spheres are oxygen, the blue ones are nitrogen, and the green ones are fluorine. d. Write the rate law for the overall reaction if the first step is the slow, rate-determining step. [Section 14.5]

Domanda del libro di testo

(a) What are the units usually used to express the rates of reactions occurring in solution?

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