What is true about intermediates in a multi-step reaction mechanism?

What is true about intermediates in a multi-step reaction mechanism?

• A. They are produced in the middle of the reaction and consumed before the end
• B. They appear in the overall balanced equation
• C. They are always catalysts
• D. They accumulate throughout the reaction

Answer: (A)

Intermediates are transient species that show up in the individual steps of a mechanism, formed in one step and consumed in a later one. Because they are produced and then used up before the reaction finishes, they do not appear in the overall balanced equation. That makes the statement that they’re produced in the middle of the reaction and consumed before the end the best description. They aren’t catalysts—they’re not regenerated unchanged to appear again; catalysts appear in the mechanism but are present at the end of the reaction as well. Intermediates also don’t accumulate throughout the process; they’re continually formed and then consumed as the mechanism proceeds, leaving no lasting presence in the net equation.

Intermediates are transient species that show up in the individual steps of a mechanism, formed in one step and consumed in a later one. Because they are produced and then used up before the reaction finishes, they do not appear in the overall balanced equation. That makes the statement that they’re produced in the middle of the reaction and consumed before the end the best description.

They aren’t catalysts—they’re not regenerated unchanged to appear again; catalysts appear in the mechanism but are present at the end of the reaction as well. Intermediates also don’t accumulate throughout the process; they’re continually formed and then consumed as the mechanism proceeds, leaving no lasting presence in the net equation.