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Chemistry Essay, Research Paper

Rates of Chemical Reactions 1:


The rate of a chemical reaction is the derivative of the extent of the reaction with respect to time, to measure the effect of concentration upon the rate of the reaction of peroxydisulfate ion with iodine ion; to determine the order of the reaction with respect to the reactant concentrations; and to obtain the rate law for the chemical reaction.

II-Material and :

Four reaction solutions are prepare as:

-solution 1:

25.0 mL KI solution

1.0mL starch solution

1.0mL Na2S2O3 solution

1 drop of EDTA solution

Total volume = 75.0 mL

-solution 2:

25.0 mL KI solution

1.0mL starch solution

1.0mL Na2S2O3

23.0 mL KNO3

1 drop EDTA solution

Total volume = 50.0 mL

-solution 3:

50.0 mL KI solution

1.0mL starch solution

1.0mL Na2S2O3 solution

23.0 mL KNO3 solution

1 drop EDTA solution

Total volume = 75.0 mL

- solution 4:

12.5 mL KI solution

1.0mL starch solution

1.0mL Na2S2O3 solution

35.5 mL KNO3 solution

1 drop EDTA solution

Total volume = 50.0 mL


1-Dilute 5 mL of 0.2 M KI solution with 10 mL of distilled water in a test tube, add 3 drops of starch solution and mix thoroughly, and then add 5 mL of 0.2 M (NH4)S2O8 solution. Mix. Wait a while and observe color changes.

2-Repeat the procedure in (1), but when the solution changes color add 4 drops of 0.4 M Na2S2O3, mix the solution, and note the effect that the addition of Na2S2O3 has on the color.

Rate Measurements:

Prepare solution 1 in a 250-mL Erlenmeyer flask that has been scrupulously cleaned and dried. Pipet 25.0 mL of (NH4)2S2O8 solution into a clean, dry 100-mL beaker. Be ready to begin timing the reaction when the solutions are mixed. The reaction starts the moment the solutions are mixed! Be prepare! ZERO TIME! Quickly pour the 25.0mL of (NH4)2S2O8 solution into solution 1 and swirl vigorously note the time you begine mixing to the nearest second. At the instant when the blue black color appears,

2 x10-4 mole of S2O8 -4 has reacted. IMMEDIATELY ( be prepare!) add a 1-mL aliquot of Na2S2O3 solution from the pipet and swirl the solution; the color will disappear.

Record the time for the reappearance of the blue black color. Add an other 1 mL aliquot of Na2S2O3 solution and note the time for the reappearance of the color. The time interval being measured is that between the appearance of the black color. For good results, these aliquots of Na2S2O3 must measured as quickly, accurately, and reproducibly as possible. Continue this procedure until you have added seven (7) aliquots to solution 1.

You are finished with solution 1 when you have recorded all your times on the report sheet. ( the time intervals are cumlative.)

Solution 2, 3, 4 should be treated in exactly the same manner except that 50.0 mL portions of ( NH4)2S2O8 solution should be added to solution 3. (CAUTION: Be on guard- solution 3 will react much more rapidly than solution 1.) In each of these reactions the final total solution volume is 100 mL.


Solution 1solution 2solution 3solution 4

Time 3.23 2.26 1.27 4.55

(sec) 6.49 6.01 3.06 9.55

interval 10.30 9.41 4.48 15.08

14.19 13.29 6.34 20.35

18.17 17.29 8.26 26.17

22.30 21.51 10.20 32.05

26.54 26.35 12.16 38.30

31.36 45.13

V- calculation:

I2 + 2S3O3-2 ——–* 2I- + S4O6-2

Slope of solution 1:

(10-4) x 10-4 mole

slope= ————————— = 2.0 x 10-5 mole/sec

(250 ? 220 ) sec

Slope of solution 2:

(7.3 ? 2.0) x 10-4mole

slope= ————————— = 1.06 x 10-5 mole/sec

(250 ? 200) sec

slope of solution 3:

(8.0-2.0) x 10-4mole

Slope= ————————— = 2.0 x 10-5 mole/sec

(110-100) sec

slope of solution 4:

(10.0 ? 6.0) x 10-4mole

slope= ——————————– =1.3 x 10-5 mole/sec

(365 ? 355) sec


Since temperature is really a measure of the average kinetic energy of the molecules of a substance, a higher temperature translates into higher kinetic energy which leads to faster moving molecules. Since the molecules are moving faster, they have a higher chance of successfully colliding and completing a chemical reaction. Thus, a higher temperature allows for a faster rate of chemical reaction.

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