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RATE OF REACTION Aplication 1. Explain why potatoes fried in boiling oil cook faster than potatoes boiled in boiling water? Answer: - Boiling point of oil is higher than boiling point of water - At higher temperature potatoes is faster to cook 2. Based on the collision theory, explain why we need to store fresh milk in refrigerator. Answer:

(i) the temperature inside the refrigerator is lower (ii) bacteria are not active at low temperature (iii) decomposition of milk caused by bacteria will slow down (iv) this will keep the milk fresh for along time

Collision theory 1. as temperature increases , the kinetic energy of the particles ( H+, S2O32- ) increases / the smaller the size of particles , the larger the total surface area / the higher the concentration of the solution , the greater the number of particles per volume 2. frequency of collision between particles increases 3. frequency of effective collision increases 4. rate of reaction increases

1.The presence of catalyst provide an alternative pathway / route 2. with a lower activation energy 3. frequency of effective collision increases 4. rate of reaction increases Note :

1. Catalyst a substance which alters the rate of chemical reaction while remains chemically unchanged at the end of reaction.

2. Observable changes for measuring the rate of reaction. - volume of gas liberated - precipitate formation - change in mass during reaction, co lour ,temperature, pressure

Efective collision - collision which achieve activation energy (minimum amount) and with correct orientation. 1. Catalyst (Manganese (IV) oxide)

1. Decomposition of sodium chlorate (V), 2NaClO3 2NaCl + 3O2 2. Decomposition hydrogen peroxide , 2H2O2 2H2O + O2

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Experiment 1.3 Aim : To investigate the effect of temperature of sodium thiosulphate Na2S2O3 solution on the rate of reaction Problem Statement: How does temperature of sodium thiosulphate Na2S2O3 solution affect the rate of reaction? Hypothesis: When the temperature of sodium thiosulphate Na2S2O3 solution increases, the rate of reaction increases.// the higher the temperature of sodium thiosulphate solution, the higher the rate of reaction. Variables: Manipulated : Temperature of sodium thiosulphate solution. Responding : Rate of reaction/ Time taken for the cross X to disappear from the sight. Fixed: Concentration and volume of sulphuric acid, concentration and volume of sodium thiosulphate solution. Apparatus : 100 cm3 connical flask, 50 cm3 measuring cylinder,10cm3 measuring cylinder, stopwatch, thermometer, Bunsen burner, tripod stand, wire gauze. Materials: 0.2 mol dm-3 sodium thioulphate solution, 1.0 mol dm-3 sulphuric acid, white paper marked X at the centre. Procedure:

1. 50 cm3 of 0.2 mol dm-3 sodium thiosulphate solution is measured using measuring cylinder and poured into a conical flask. 2. The temperature of the solution is measured with a thermometer. 3. The conical flask is placed on a white paper marked`X`. 4. 5 cm3 of 1 mol dm-3 sulphuric acid is measured using measuring cylinder. 5. The acid is quickly and carefully poured into the sodium thiosulphate solution. 6. The stopwatch is started immediately and the conical flask is swirled. 7. The mark `X` is viewed / observed vertically from above. 8.The stopwatch is stopped as soon the mark disappear from sight. 9.Time taken is recorded. 10. Steps 1 to 9 are repeated by using the different temperature of sodium thiosulphate solution

at 400C,500C, 550C and 600C. Other conditions were kept unchanged.

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Data and Observation Experiment Temperature ,

(oC) Time taken for the X mark to disappear from view, t (s)

1/ time taken , 1/t ( s-1)

1 28 55 0.018 2 35 36 0.028 3 40 23 0.043 4 45 17 0.059 5 50 13 0.077

Discussion Based on plotted graph: [ calculation ] The higher the temperature of sodium thiosulphate, the shorter the time taken for crossX to disappear from the sight. The rate of reaction directly proportional to the temperature of sodium thiosulphate solution used. // As the temperature sodium thiosulphate solution increases, the time taken decreases. Therefore the rate of reaction increases. Conclusion : The rate of reaction increases as the temperature sodium thioulphate solution increases.

Energy profile diagram Aim: to investigate effect of catalyst on the rate of decomposition hydrogen peroxide. Problem statement: how does a catalyst affect the rate of decomposition hydrogen peroxide Hypothesis: manganese (IV) oxide, MnO2 increases the rate of decomposition of hydrogen peroxide

Variables:

Manipulated : presence of manganese (IV) oxide (MnO2) Responding : rate of reaction Fixed : concentration of H2O2, initial temperature of H2O2 solution.

Apparatus: test tube, 10 cm3 measuring cylinder, test tube rack, spatula. Materials: 20 volume of H2O2 solution, manganese (IV) oxide (MnO2) powder, wooden splinter

1. Ea activation energy without catalyst 2. Ea - activation energy with catalyst 3. Exothermic reaction heat released /given out 4. Energy content in reactants higher than products 5. ^ H is the energy difference in reactants and products 6. Heat given out during bond formation is greater than heat absorbed during bond breaking

- ^ H

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Procedures: 1. label two test tube as A and B 2. Using a measuring cylinder measure 5 cm3 of 20 volume of H2O2 solution and pour

into test tube A. 3. Repeat the same procedure for test tube B. 4. Add 1 spatula of manganese (IV) oxide powder into test tube B. 5. Shake the two test tubes and place them in a test tube rack. 6. immediately hold a glowing splinter separately at the open edge of each the two test

tubes 7. Observe and record the changes.

Observation:

Test tube Observation A No effervescence. the glowing wooden splinter did not relight B Effervescence occurred. The glowing wooden splinter relight and burn brightly

Discussion:

Manganese (IV) oxide (MnO2) increases the rate of decomposition of hydrogen peroxide. Decomposition of hydrogen peroxide produces oxygen gas. 2H2O2 2H2O + O2