Question

4. Kinetics: Suppose you are trying to create a demonstration for elementary school students. You have a particular reaction in mind: decomposing hydrogen peroxide in the presence of soapy water creates bubbles and fizzing. However, the reaction is very, very slow. Describe some ways that you could make this reaction go faster using the following criteria. [A] Concentration - how should you change the concentration of peroxide to speed the reaction up? Explain why you proposed what you did. (B) Temperature - at what temperature (hotter or colder) should you do this reaction? Explain why you proposed what you did. [C] Catalysis -Should a catalyst be used to speed up the reaction? Explain why you proposed what you did.

Answer 1

Hydrogen peroxide decomposes to produce oxygen and water in the presence of soapy water. However this is a very slow process and takes very long time.

The following are the some ways in which this reaction can be made faster:

[A] Increasing the Concentration of Hydrogen Peroxide

The decomposition reaction is as follows:

2 H₂O_{​​​​2}(aq) -> 2 H₂O(l) + O_{​​​​​​2}(g)

The rate law expression can be written as

rate= k[H_{​​​​​​2}​​​​​O_​2]^a

As tje concentration of the reactants is directly proportional to the rate of the reaction, increasing the concentration of Hydrogen Peroxide will increase the reaction rate.

[B] Increasing the temperature

At room temperature, this reaction happens at a rate so slow that, for practical purposes, it may as well not even exist. Therefore the temperature is increased to speed things up.

[C] Adding a Catalyst

The iodide ion (I-) present in potassium iodide or sodium iodide can be used as a catalyst to speed up the decomposition of hydrogen peroxide.

The catalysed reaction is,

H₂O_{​​​​2} (aq) + I-(aq) --> H₂O(l) + IO-(aq)

IO-(aq) + H₂O_{​​​​2} (aq) --> H₂O(l) + O_{​​​​​​2} (g)

The overall reaction is as follows:

2 H₂O_{​​​​2} (aq) --> 2 H₂O(l) + O_{​​​​​​2} (g)

The use of the catalyst increases the rate of the reaction and hence should be used.