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Edexcel A-Level Chemistry A2 11.1 The Terms I Rate of Reaction Ii Rate Equation Rate K a M B N Where M and N Are 0 1 Or 2 Iii Order with Respect to Questions

Read each exponent as the order for that reactant, add exponents for overall order and rearrange the rate equation before deriving the units of k.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Write a rate equation from individual orders and state the overall reaction order.
  • Calculate k and derive its units from the rate units and overall order.
  • Predict a rate factor when one or more reactant concentrations are multiplied.

Edexcel A-Level Chemistry A2 11.1 The Terms I Rate of Reaction Ii Rate Equation Rate K a M B N Where M and N Are 0 1 Or 2 Iii Order with Respect to Questions question 1

[Maximum number: 3]

A group of students investigated the kinetics of a 'clock' reaction.
The reaction investigated was that between hydrogen peroxide and iodide ions in the presence of acid.

Reaction 1H2O2(aq)+2H+(aq)+2I−(aq)→2H2O(l)+I2(aq)1 \quad \mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+2 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{I}^{-}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{I}_{2}(\mathrm{aq})

In this 'clock' reaction, a fixed volume of aqueous sodium thiosulfate, Na2 S2O3\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}, and a small amount of starch were added to the reaction mixture.

The added thiosulfate ions react with the iodine produced in Reaction 1.

Reaction 22 S2O32−(aq)+I2(aq)→S4O62−(aq)+2I−(aq)22 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-}(\mathrm{aq})+\mathrm{I}_{2}(\mathrm{aq}) \rightarrow \mathrm{S}_{4} \mathrm{O}_{6}^{2-}(\mathrm{aq})+2 \mathrm{I}^{-}(\mathrm{aq})

When all the thiosulfate ions have reacted, the presence of iodine is detected by the formation of a starch-iodine complex. The students recorded the time taken for this complex to form.

Question (a)

(a)

Four reaction mixtures, with different initial concentrations of hydrogen peroxide, hydrogen ions and iodide ions, were prepared.

Each mixture had the same volume and contained the same amount of sodium thiosulfate and starch.

Table for Question (a) — Edexcel A-Level Chemistry A2
[ 3 ]

Question (i)

(i)

Write the overall rate equation for Reaction 1 using your answers to (b)(i).

[ 1 ]

Question (ii)

(ii)

Calculate a value for the rate constant of Reaction 1 using data from Mixture 1 and your answers to (b)(ii) and (b)(iv).
Include the units of the rate constant.

[ 2 ]
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