Date Section Name A Study of Reaction Rates Post Lab Questions The iodine clock

Question

Date Section Name A Study of Reaction Rates Post Lab Questions The iodine clock reaction you studied today is considered to be an irreversible reaction when the reactants are converted to products, there is no reverse reaction to re-form reactants from the products. What would happen to the color of the solution if the reaction were reversible? 1. Consider the generic reaction below, where a dilute aqueous solution of "A" reacts with water, the solvent. Explain why, even though water is a reactant, increasing the amount of water is likely to decrease the reaction rate. 2. A(aq) + H2O(I) B(aq) The "strike anywhere" type of matches usually have their tips coated with phosphorus, which makes it easier for them to light with less friction than regular matches. The phosphorus helps initiate the combustion reaction, but it should not be considered to be a catalyst. Why not? 3. 4. Considering the principles of collision theory a. Explain why increasing the concentration of reactant increased reaction rate. b. Explain why increasing temperature lead to increased reaction rates. Revised 1/17/1T

Explanation / Answer

1. As the reaction is irreversible, the color of the solution formed by Iodine clock reaction is purple. But if the reaction would have reversible. then it would lie in between purple and colorless, i.e. blue. The solution would have been blue.

2. In this reaction, water is acting as a solvent. So, if we increase the amount of water, the reactant molecules, i.e. A, will become farther from each other and thus, it would be difficult for them to react. There will be less collisions between them, according to collision theory, and thus the reaction rate will decrease.

3. Generally, catalyst is a substance which helps in fasten the reaction but does not take part in the reaction. The meaning is that the catalyst can be obtained back in its original identity once the reaction gets completed. In strike anywhere matches, phosphorus is initiating the reaction and can not be recovered back after the whole burning. This makes phosphorus as reactant and not catalyst, as it is being consumed in the reaction.

4. a. On increasing the reactant concentration, the rate of the reaction increases, because the probability of collisions between the reactants also increase. There are more chances, that the reactants will collide in right orientation to produce products. So, increase in reactant concentration increases the rate of reaction.

b. On increasing the temperature of the reaction, the thermal energy of the reactants increase. This ultimately increases the kinetic energy of the reactants and speed of the reactants increases. So, number of collisions will also increase in a specified time and thus more of products will be formed. Therefore, the rate of reaction increases with increase in temperature.

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