Aim for FiveChemistry

Short free-response question

Decomposition of hydrogen peroxide

  • Unit 5
  • 4 points
  • About 9 minutes

You can use a calculator on this question, just like on exam day.

A shorter multipart question that sticks to one or two topics. Each part usually asks for one calculation, claim or explanation. On the exam: 4 questions (Questions 4–7), part of the 1-hour-45-minute free-response section; calculator allowed.

The question and its sources

Hydrogen peroxide decomposes according to the equation 2 H₂O₂(aq) → 2 H₂O(l) + O₂(g). A student measured [H₂O₂] over time at constant temperature.

Table 1. Concentration of H₂O₂ over time

Time (min)[H₂O₂] (M)
00.640
150.422
300.279
450.184
600.121

Source: Hypothetical data

Suggested time: 9 minutes

Your answers are saved in this browser as you type.

Part (a)

1 point

The reaction is first order with respect to H₂O₂. Describe the graph you would plot using the data in Table 1 to confirm this. Include what is plotted on each axis, the shape that would confirm first order, and what the slope represents.

0 / 2,500 characters

Part (b)

1 point

Calculate the value of the rate constant, k. Include units with your answer.

0 / 2,500 characters

Part (c)

1 point

Calculate [H₂O₂] at t = 100. minutes.

0 / 2,500 characters

Part (d)

1 point

When a small amount of KI(aq) is added, O₂ is produced much faster; I⁻ acts as a catalyst. Explain how a catalyst increases the rate of the reaction, and state how the half-life of H₂O₂ changes.

0 / 2,500 characters

Checking scoring…

Scoring it yourself shows you the rubric, examples and a model answer. Try writing your answer first.