Rate-determining step 124-125

Question 1

Define reaction mechanism

Answer 1

A reaction mechanism is a series of steps that, together, make up the overall reaction.

Question 2

Define rate-determining step

Answer 2

The rate-determining step is the slowest step in the reaction mechanism of a multi-step reaction.

Question 3

Explain the rate-dermining step ( not asking for definition.).

Answer 3

Multi-step reactions often have one step that is much slower than the others.

• A slow step becomes an obstacle to the whole process - reactants can become products only as fast as the y can get through this slow step.
• The overall reaction can be no faster than the slowest step.

The rate of reaction is dominated by this slow step.

Question 4

Define intermediate.

Answer 4

An intermediate is a species formed in one step of a multi-step reaction that is used up in a subsequent step, and is not seen as either a reactant or a product of the overall equation.

Question 5

Explain how calculating the rate equation of a reaction allows the reaction mechanism to be calculated.

Answer 5

When you have have calculated the rate equation:

rate = k[NO₂]²

If a reactant appears in the rate equation, that reactant is involved in the rate-determining step.

The order with respect to the reactant tells you how many particles of the reactant are involved in the rate-determining step. For the above rate equation we know two molecules of NO₂ are involved.

Question 6

Predict the reaction mechanism for the reaction:

NO₂(g) + CO(g) → NO(g) + CO₂(g)

knowing the rate equation, rate =k[NO₂]²

Answer 6

The answer is on the worked example of page 124 of the chemistry book.