Increase In The Reaction Rate example essay topic

Investigating Rate of Reaction between Iodide ions and Peroxodisulphate ions with respect to Temperature and use of a Catalyst Introduction The aim of this experiment was to investigate the affect of the use of a catalyst and temperature on the rate of reaction while keeping all the other factors that affect the reaction rate constant. In the reaction, potassium and potassium iodide will be used to provide the ions and iodide ions respectively. The ionic formula for the reaction is as follows: S 2 O 82- (aq) + 2 I- (aq) 2 SO 42- (aq) + I 2 (aq) However, in order to measure the rates of reaction, sodium and starch are added. Sodium is added to react with a certain amount of iodine as it is made.

Without the, the solution would turn blue / black immediately, due to the iodine and starch. The ions allow the rate of reaction to be determined by delaying the reaction so that it is practical to measure the time it takes for the iodine to react with the. After the all the has reacted with the iodine, the free iodine displays a dark blue / black colour with the starch. If t is the time for the blue / black colour to appear, then 1/t is a measure of the initial rate.

While measuring the effect of the use of a catalyst and temperature on the reaction rate, several factors must be kept constant. During the reaction with a catalyst, the temperature will be kept constant (at room temperature), concentration, pressure and since the reaction involves liquids, the surface area will be kept constant at all times, however they must be mixed the same. Predictions may be made about the suitability of possible catalysts by assuming that the mechanism of catalysis consists of two stages, either of which can be first: o The higher oxidation state of the catalyst oxidizes I- (aq) o The lower oxidation state of the catalyst reduces S 2 O 82- Hypothesi so The use of a catalyst will speed up the reaction as long as the catalysts electrode potentials are feasible for each step in the reaction. Since a catalyst lowers the activation energy and takes the reaction through a different route, according to the Maxwell-Boltzmann diagram, at a constant temperature more particles are able to react as demonstrated by the diagrams below: T = Temperature An increase in the temperature of the system will increase the rate of reaction. Again, using the Maxwell-Boltzmann distribution diagram, we can see how the temperature affects the reaction rate by seeing that an increase in temperature increases the average amount of energy of the reacting particles, thus giving more particles sufficient energy to react. In general, an increase in temperature of 10 K leads to a double the reaction rate.

T = Temperature Method and ApparatusApparatuso Four Burettes Conical flask o Boiling tube o 0.20 M Potassium Iodide solution 0.01 M Sodium Thiosulphate solution 0.20 M Potassium Peroxodisulphateo Starch Solution (0.2%) o Water bath (30 oC- 50 oC) o Thermometer Catalysts: o Cr (VI) and Cr ( ) ion so Mn (VII) and Mn (II) ion so Fe ( ) and Fe (II) ions Method 1: Testing the catalysts 1. In a test tube, mix a few drops of potassium iodide solution with a few drops of dilute sulphuric acid. Add a few drops of one of the transition metal in a higher oxidation state and look for the evidence of a reaction. Repeat this for all the transition metals with a higher oxidation state. 2.

In a test tube mix a few drops potassium solution with a few drops of a solution containing the same transition metal in a lower oxidation state and look for the evidence of a reaction. Repeat with the other transition metals with a lower oxidation state. Method 2: Investigating the rate of reaction 1. Fill the four burettes with one of each of the following solutions: o 0.20 M potassium iodide solution 0.01 M Sodium solution 0.20 M potassium Starch solution (0.2%) 2.

From the burettes, run into a conical flask these volumes: o 10 cm 3 of potassium iodide solution 10 cm 3 of sodium solution 5 cm 3 of starch solution 3. Run 20 cm 3 of potassium solution into a boiling tube. 4. Quickly pour the contents of the boiling tube into the flask and start timing. Swirl the flask a few times to mix the solutions evenly and wait for the first sign of a blue / black colour to appear. Record the time for the reaction.

5. Repeat this process, however, add a few drops of a catalyst to the first three reagents, or increase the temperature of the system by putting the solutions in a water bath of a fixed temperature before mixing (check the temperature of the water baths and the solutions with a thermometer to ensure accuracy). 6. Repeat the procedure to obtain reliable results. Data Collection and Results Experiment 1: The effect of temperature Temp. (K) 293 303 313 323 Time (s) 94 50 27 15 Experiment 2: The use of a catalyst Transition metal Cr Mn Fe Time (s) (Higher oxidation State) 105 96 27 Time (s) (Lower oxidation state) 79 80 29 As predicted, an increase in temperature led to an increase in the reaction rate.

Furthermore, an increase of 10 K doubled the rate of reaction, which is concordant with the Maxwell-Boltzmann distribution diagram.