Factors Affecting the Rate of Reaction: An Iodine Clock Reaction The rate of a r

Question

Factors Affecting the Rate of Reaction: An Iodine Clock Reaction The rate of a reaction describes how fast a reactant decomposes to form a product or how fast the product forms. Factors that affect the rate of reaction are concentration, temperature, surface area, and the addition of a catalysis. In today's lab, the reaction between potassium persulfate (K2S20s "A") with sodium iodide (Nal "B") to form iodine D') will be studied. This reaction is called the lodine Clock Reaction. S20's 21 2SOA A 2B 20 D Then in a second reaction: L+ 2s2012- 21 Do 2E 2B F Overall A, 2E 2C +F A starch solution serves as an indicator of the end of the 2nd reaction after all the S203 ("E") is used up, forming a dark-blue colored starch-iodine complex in the presence of iodine. (D) starch dark blue colored starch-iodine complex When this is used up, the Iodine reacts with Starch. Starch Blue Complex This color appears so abruptly that it can be as startling as the sudden sound of the alarm bell of a clock. As the concentration changes, the time it takes for the appearance of the dark blue color will change.

Explanation / Answer

I am providing an explanation of how to solve for the questions, which should make it wasy for you to solve.

(1)

Order of reaction for a particular reactant ( say 'A' ) is determined by holding the conc. of other reactants constant and changing the conc. of A by a constant factor. Lets say we double the conc. of A, keeping other reactant conc. unaffected. If the rate also doubles, then the reaction is of order 1 with respect to A. If rate remains constant, then reaction is of order zero with respect to A. In this way we check for the reaction order for other reactants as well.

(2)

Let's assume that reaction is of order 'm' with respect to A, and of order 'n' with respect to B.

The rate equation is thus:

r = k*[A]m*[B]n

(3)

Consider the case of the reaction is above part. For this case, overall reaction order is sum of reaction orders for all reactant species. Thus for this reaction overall order is (m+n).

(4)

For calculating the rate constants, just plug in the values in the rate equations. This will give the value of 'k'

(5) & (6) have to be done in a similar way as described above.

(7)

Arrhenius equation is used to determine the activation energy:

k = A*e(-E/RT)

Here A is a constant called Arrhenius constant.

E is the activation energy, R = gas constant = 8.314 J/(mol.K) , T = absolute temp. in Kelvins

Switch in the values to calculate E.

(9)

Addition of a catalyst lowers the activation energy required for the reaction. It does so by providing an alternative pathway for the reaction to take place which has lesser threshold energy requirement.

Hope this helps. Revert back if you have any queries.

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