A proposed mechanism for the reaction of NO2 and CO is Step 1 Slow, endothermic 2 NO2(g) ⟶NO(g)+

step 1 In this problem, we're given an elementary reaction mechanism and asked to determine if these fi

A proposed mechanism for the reaction of NO2 and CO is Step...

A proposed mechanism for the reaction of $\mathrm{NO}_{2}$ and $\mathrm{CO}$ is Step 1 Slow, endothermic $$2 \mathrm{NO}_{2}(\mathrm{g}) \longrightarrow \mathrm{NO}(\mathrm{g})+\mathrm{NO}_{3}(\mathrm{g})$$ Step 2 $\quad$ Fast, exothermic $$\mathrm{NO}_{3}(\mathrm{g})+\mathrm{CO}(\mathrm{g}) \longrightarrow \mathrm{NO}_{2}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{g})$$ Overall Reaction Exothermic $$\mathrm{NO}_{2}(\mathrm{g})+\mathrm{CO}(\mathrm{g}) \longrightarrow \mathrm{NO}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{g})$$ (a) Identify each of the following as a reactant, product, or intermediate: $\mathrm{NO}_{2}(\mathrm{g}), \mathrm{CO}(\mathrm{g}), \mathrm{NO}_{3}(\mathrm{g}), \mathrm{CO}_{2}(\mathrm{g})$ $\mathrm{NO}(\mathrm{g})$ (b) Draw a reaction coordinate diagram for this reaction. Indicate on this drawing the activation energy for each step and the overall reaction enthalpy.

A proposed mechanism for the reaction of $\mathrm{NO}_{2}$ and $\mathrm{CO}$ is Step 1 Slow, endothermic
$$2 \mathrm{NO}_{2}(\mathrm{g}) \longrightarrow \mathrm{NO}(\mathrm{g})+\mathrm{NO}_{3}(\mathrm{g})$$
Step 2 $\quad$ Fast, exothermic
$$\mathrm{NO}_{3}(\mathrm{g})+\mathrm{CO}(\mathrm{g}) \longrightarrow \mathrm{NO}_{2}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{g})$$
Overall Reaction Exothermic
$$\mathrm{NO}_{2}(\mathrm{g})+\mathrm{CO}(\mathrm{g}) \longrightarrow \mathrm{NO}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{g})$$
(a) Identify each of the following as a reactant, product, or intermediate: $\mathrm{NO}_{2}(\mathrm{g}), \mathrm{CO}(\mathrm{g}), \mathrm{NO}_{3}(\mathrm{g}), \mathrm{CO}_{2}(\mathrm{g})$ $\mathrm{NO}(\mathrm{g})$
(b) Draw a reaction coordinate diagram for this reaction. Indicate on this drawing the activation energy for each step and the overall reaction enthalpy.

Key Concepts

Enthalpy Change (Exothermic and Endothermic Processes)

Enthalpy change reflects the overall heat absorbed or released during a reaction. An endothermic process absorbs heat, typically associated with an increase in energy and a positive enthalpy change, while an exothermic process releases heat, leading to a decrease in energy and a negative enthalpy change. Analyzing the enthalpy changes in individual steps provides insights into the thermodynamics of the reaction mechanism.

Activation Energy

Activation energy is the minimum energy barrier that must be overcome for a chemical reaction to proceed. It is the energy difference between reactants and the highest energy transition state along the reaction path. Each elementary step in a mechanism has its own activation energy, which significantly influences the rate at which that step occurs.

Rate-Determining Step

The rate-determining step is the slowest elementary step in a reaction mechanism that limits the overall reaction rate. Since it has the highest activation energy barrier relative to the other steps, it controls the speed at which the overall reaction proceeds, and understanding it is essential for kinetics analysis.

Reaction Intermediates

Reaction intermediates are species that are produced and consumed during the course of a multi-step reaction mechanism. They do not appear in the overall balanced equation because they exist only transiently while the reaction proceeds. Their identification is key to understanding and controlling the pathway of a reaction.

Reaction Mechanism

A reaction mechanism is the detailed, step-by-step pathway by which reactants transform into products. It includes the identification of elementary steps, processes through which the overall reaction occurs, and can reveal the formation of short-lived intermediate species. Understanding the mechanism provides insight into the reaction kinetics and energy changes involved in each step.

Reaction Coordinate Diagram

A reaction coordinate diagram is a graphical representation that depicts the energy changes throughout the course of a chemical reaction. It plots the potential energy of the system against the progress of the reaction, illustrating the energy levels of reactants, intermediates, transition states, and products. Such diagrams help visualize activation energies and the overall reaction enthalpy change.

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