waja chp.1rate of reaction

WAJA F5 Chemistry 2010 Chapter 1 : Rate of Reaction

CHAPTER 1 : RATE OF REACTIONS

A Rate of Reaction

Learning OutcomesYou should be able to :

state what rate of reaction is identify observable changes to reactants or products for determining rate of reaction determine the average rate of reaction determine the rate of reaction at any given time from a graph solve numerical problems involving average rate of reaction. solve numerical problems involving rate of reaction at any given time.

Activity 1 : What is rate of reaction?

Rate of reaction is the ……………… at which reactants are converted into .………………….

in a chemical reaction.

The rate of reaction is a measurement of the change in the quantity of …………………. or

…………………………. against time.

Rate of reaction = Change in quantity of reactant /Product

Time taken

Activity 2 : Fast (F) or Slow (S) reactions? Write F for the fast reaction and S for the slow reaction.

1. Fading of dyes on a shirt under hot sun

6. Striking a match

2. A piece of paper turning yellow 7. Rusting of a water pipe

3. Frying an egg 8. Ripening of tomatoes

4. The weathering of limestone by acid rain

9. Digesting food

5. Burning of petrol in a car engine 10. Cooking a chicken using microwave oven

Activity 3 : Observable changes for measuring the rate of reaction

The change in amount of reactant / product that can be measured by :

…………………………….. in the mass of reactant

…………………………….. in mass of product

…………………………….. in volume of gas released

…………………………….. of precipitate

Change in pH, temperature or electrical conductivity

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For each of the reactions below, write a chemical equation and state the observable change/changes can be used as selected quantities to measure the rate of reaction :

Example 1 : The reaction between marble chip with hydrochloric acid to produce carbon dioxide gas and chloride salt.

Chemical Equation : ……………………………………………………………………………….

Changes :

(i) ………...………………………………………………………………………... (reactants)

(ii) …………………………………………………………………………………….(product)

Example 2 : Reaction between sodium thiosulphate solution with sulphuric acid to produce

yellow precipitate of sulphur, water , sulphur dioxide and sodium sulphate solution.

Chemical equation : ………………………………………………………………………………..

Change :

(i) …………………………………………………………………………………… (product)

Example 3 : Decomposition of hydrogen peroxide to produce water and oxygen gas.

Chemical equation : ………………………………………………………………………………..

Change :

(i) …………………………………………………………………………………… (product)

Activity 4 : Determine the Rate of Reaction.4A1. Two ways to measure the rate of reaction.

Average rate of reaction = Increase in the amount of product/decrease in the amount of reactant Time taken for the change to occur

2. a) Determination of average rate of reaction from the graph:

2Time (s)

Volume of gas (cm3)

V3

V2

V1

60 120 240

180

V4Overall Average rate of reaction

Total Volume of gas collected = V4

Time taken for the reaction = 240 s

Average rate of reaction = cm3s-1


b) Instantaneous rate of reaction (Rate of reaction at any given time)

The rate of reaction at t sec

= gradient of the curve at t sec = a cm3s-1

b

c) Determining the rate of reaction at any given time

3

Average rate of reaction in the first two minutes

= volume of gas collected in the first 120 seconds (cm 3 ) time taken (s)

= cm3s-1

Average rate of reaction in the third minute

Volume of gas collected in the first 180 sec = V3

Volume of gas collected in the first 120 sec = V2

Volume of gas collected in the third minute = ____________ cm3

Time taken for the reaction = 180 – 120 = _______ s

Average rate of reaction in the third minute = m3s-1

Time (s)

Volume of gas (cm3)

V1

30120

160

V2 Instantaneous rate of reaction / the rate of reaction at 120 sec

= gradient of the curve at 120 sec = cm3s-1

WAJA F5 Chemistry 2010 Chapter 1 : Rate of Reaction4B

1. In the experiment to determine the rate of reaction between marble chips and hydrochloric acid, the volume of oxygen gas collected at intervals of 0.5 minutes is recorded in the table below :

Time (min) 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Volume of oxygen gas(cm3)

0.00 27.00 46.00 59.00 70.00 79.00 86.00 92.00 95.00 95.00 95.00

Plot a graph of the volume of gas collected against time.

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30

40

50

10

60

70

80

90

100

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Graph of volume of oxygen gas liberated against time

Volume of gas (cm3)

Time (min)

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0


2. Based on the graph plotted, determine

(i) the average rate of reaction in the first 3 minutes

(ii) the average rate of reaction in the third minutes

(iii) the overall average rate of reaction

(iv) the instantaneous rate of reaction at 1 minute

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Activity 5

1. The following figure shows the graph of carbon dioxide, CO2 gas produced when an excess of calcium carbonate, CaCO3 reacts with 40 cm3 of 0.1 moldm-3 hydrochloric acid, HCl.

(a) Calculate the

(i) Average rate of reaction in the first 10 sec

(ii) Average rate of reaction in the first 30 sec

(iii) Overall average rate of reaction

(b) Based on the results in (a), how does the rate of reaction change with time.

……………………………………………………………………………………………………………………..

(c) Explain your answer in part (b) with respect to the concentration of hydrochloric acid.

……………………………………………………………………………………………………………………..

………………………………………………………………………………………………………………………

2. The following table shows the volume of a gas collected from an experiment.

Time (s) 0 30 60 120 150Volume of gas (cm3) 0.00 17.00 29.00 36.00 36.00

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Calculate th average rate of reaction for

(a) the first 60 seconds (b) the overall reaction

3. The decrease in mass of a reaction mixture is recorded in the following table.

Time (min) 0 1 2 3 4 5Mass of reaction mixture (g) 2.90 1.90 1.25 0.75 0.40 0.10

(a) Draw a graph of mass of reaction mixture against time.

(b) Calculate the rate of reaction at the third minute.

B FACTORS AFFECTING THE RATE OF REACTION

Learning OutcomesYou should be able to : design experiments to investigate factors affecting the rate of reaction. give examples of reactions that are affected by size of reactant, concentration, temperature and catalyst. explain how each factor affects the rate of reaction. describe how factors affecting the rate of reaction are applied in daily life and in industrial processes. solve problems involving factors affecting the rate of reaction. apply knowledge on factors affecting the rate of reaction in everyday activities.

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Activity 6 : Factors affecting the rate of reaction.

State five factors that affect the rate of reaction :

(a) ……………………………………………. (b) …………………………………………..

(c) ……………………………………………. (d) …………………………………………..

(e) …………………………………………….

Activity 7 : Speeding up the Rates of reaction.

The following changes may speed up the rate of a chemical reaction between an acid and magnesium.Put a tick in the box next to each one that will speed up the reaction (assume that there is initially an excess of acid) and state the specific factors that affect the reaction.

Statement of factors that affect the rate of reaction Specific factor1. Heating the acid…………….

2. Shaking the flask………….

3. Using more-concentrated acid …………….

4. Using powdered metal, not metal ribbon ………….

5. Using twice the volume of acid ……………

6. Using a suitable catalyst …………….

7. Increasing the pressure …………..

8. Using larger flask ……………

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Activity 8 : Experiments to investigate the rate of reaction.

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(i) Effect of size of reactants

Aim : To investigate the effect of size of reactant in an experiment between marbles and hydrochloric acid on the rate of reaction.

Equation : ……………………………………………………………………………………………..

The curve of experiment 2 is ……………………………. than experiment 1.

The rate of reaction of experiment 2 is ………………… than experiment 1

The smaller the size of reactants, the …………………………. the total surface area,

the …………………………. the rate of reaction.

Volume of gas (cm3)

Time (s)

Experiment 1 : CaCO3 chipsExperiment 2 : CaCO3 powder

Expt 1

Expt 2

Diagram of an experiment (Refer the apparatus set-up for the experiment in page 7 Practical Book)


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(ii) Effect of concentration

Aim : To investigate the effect of concentration of sodium thiosulphate solution on the rate of reaction.

Equation : …………………………………………………………………………………………………..

* The higher the concentration of the sodium thiosulphate solution, the …………………………… the time taken.

* 1/ t is ………………………………

The …………………. the concentration of sodium thiosulphate solution, the

………………………..the time taken.

Concentration (moldm-3) of sodium thiosulphate solution

Time (s)

Concentration (moldm-3) of sodium thiosulphate solution

1/ time (s-1)


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(iii) Effect of catalyst

Aim : To investigate the effect of the presence of catalyst (Manganese (IV) oxide) on the rate of decomposition of hydrogen peroxide.

Equation : ……………………………………………………………………………………………………..

Draw the apparatus set-up for the experiment.

The curve of experiment 2 is ……………………………………………. than experiment 1.

The rate of reaction of experiment 2 is ………………………………….than experiment 1

The presence of catalyst, will …………………….................... the rate of reaction.

Volume of gas (cm3)

Time (s)

Experiment 1 : with catalystExperiment 2 : without catalyst

Expt 1

Expt 2

Diagram of an experiment


Activity 9

1.

Activity 9

1.

Activity 9

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(iv) Effect of temperature

Aim : To investigate the effect of temperature on the rate of reaction between sodium tiosulphate solution and sulphuric acid.

Equation : ………………………………………………………………………………………………………….

The higher the temperature, the ...………………………………. the time taken.

1/ time is ……………………………………………..

The ………………………….. the temperature, the …………………… the rate of reaction.

Temperature (oC)

Time (s)

Temperature (oC)

1 / time (s-1)


1

2.

Meat cut into small pieces, have ……………………….. size compare to the meat cut into big

pieces. The ……………………… the size, the bigger the ……………………………………….

of the meat, hence the …………………………………… the rate of reaction.

3. State and briefly discuss two industrial processes that make use catalyst. [8 marks ]

(i) Haber process is a chemical process to produce ……………………………… from nitrogen and

hydrogen gas. The equation of this process is …………………………………………………………...

The suitable condition of reaction are temperature : ………………………………………,

pressure : ………………………………….. and catalyst : ………………………………………………..

(ii) ……………………………… process is a chemical process of synthetisising sulphuric

acid. The equation of stage III for this process is……………………………………………..

The suitable condition of reaction are temperature : ………………………………………,

pressure : …………………………………….. and catalyst : ……………………………………………..

C COLLISION THEORY Learning Outcomes You should be able to :

relate reaction with energy produced by movement and effective collision of particles. describe activation energy. sketch and describe energy profile diagram relate the frequency of effective collisions with the rate of reaction relate the frequency of effective collisions with factors influencing the rate of reaction describe how a certain factor affects the collision of particles in a reaction

Activity 10 Understandings the Collision Theory

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[ Temperature in refrigerator is ……………………………. The lower temperature caused the bacteria

to be less ………………………. A little …………………… is released by the bacteria. The rate of the

food turns bad is …………………………. ] //

[ Temperature in kitchen cabinet is ………………………. The higher temperature caused the bacteria

to be ……………………reactive. A ………………………… toxic is released by the bacteria. The rate

of the food turns bad is ……………………………….]

Food store in a refrigerator lasts longer than food stored in a kitchen cabinet. Explain why. [4 marks]

One kilogramme of meat, cut into big pieces, takes a longer time to cook compared to one kilogramme of meat cut into small piece.

Explain the above statement based on the size of the particles. [2 marks]


1. What is collision theory ?

A theory used to explain chemical reactions in terms of

(i) ……………………………………………………………………………………………………………………

(ii) …………………………………………………………………………………………………………………..

(iii) ………………………………………………………………………………………………………………….

2. The collision theory states that :

(i) A chemical reaction occurs when the reactant particles ……………………….. each other.

(ii) Not all collision result in the formation of …………………………………

(iii) A collision is ……………………………. only when the reactant particles have enough

energy to overcome the ………………………………………………… of the reaction and

when they collide in the proper orientation.

3. What is activation energy ?

The …………………………………… energy which the colliding reactant particles must have that can result a chemical reaction.

4. Energy profile diagram

In the energy profile diagram, the activation energy is the difference in the energy between the energy of the ……………………. and the energy shown by the peak of the curve.

Activity 11

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On the diagram shown below, identify (i) the activation energy, Ea and (ii) the activation energy in the presence of catalyst, Ea’

Activity 12 Collision theory and factors affecting the rate of reactions..

(i) Effect of total surface area

When the size of a fixed mass of solid reactant is

smaller, the _____________________ exposed to

collision with the particles of the other reactants is

_____________. Thus, the frequency of collision

among the reacting particles at the surface of the

solid reactant ____________ ___. This leads to an

_________________ in the frequency of effective

collision and hence, a _____________ rate of

reactions.

(ii) Effect of catalyst

The presence of a catalyst in a chemical reaction

allows the reaction to take place through an

alternative path which requires a ______________

in activation energy which can be shown in the

energy profile diagram. Thus, the colliding

particles are able to achieve the activation energy.

This means that the frequency of effective collision

__________________and hence, a

_______________ rate of reaction

(iii) Effect of temperature

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An increase in temperature will increase the

_________________ of the reacting particles. This

leads to the following two changes. Firstly, the

particles move _________________ and collide

more often with one another. Thus, the frequency

of collision is ________________ Secondly, more

colliding particles have ____________ energy

which are enough to overcome the activation

energy. Both these factors contribute to the

_________________ frequency of effective

collision and hence, a _____________ rate of

reaction

(iv) Effect of concentration and pressure

An increase in the concentration of the solution of

a reactant or in the pressure of gaseous reactants

will result in an __________________ in the rate

of reaction. Why? When the concentration of the

solution of a reactant increases, the

_________________ of particles per unit volume

of this reactant also _______________. With more

particles per unit

volume of the solution, the frequency of collisions

per unit time between the reacting particles

__________________. Thus, the frequency of

effective collision ________________ and hence,

the rate of reaction becomes

___________________.

Use the words below to fill in the blank boxes in the diagram Bigger surface area more particles cold hot

slow less particles fast bigger size slow smaller size

Activity 13

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WAJA F5 Chemistry 2010 Chapter 1 : Rate of Reaction 1. A group of pupils carried out three experiments to investigate the factors affecting the rate of a reaction. Table below shows information about the reactants and the temperature used in each experiment.

Experiment Reactants Temperature / oC

A Excess magnesium ribbons and 25 cm3 of 0.5 mol dm-3 hydrochloric acid

25

B Excess magnesium ribbon and 25 cm3 of 0.5 mol dm-3 hydrochloric acid

35

C Excess magnesium powder and 25 cm3 of 0.5 mol dm-3 hydrochloric acid

35

Sketch a graph of these experiments on the same axes. [4 m]

2.. A student carried out three experiments to investigate the effects of the factors influencing the rate of reaction. Table below shows the results of the experiments.

Experiment I II IIISet-up of apparatus

Temperature / oC 30 40 40Time taken for all the magnesium to dissolve / s

50 20 15

Sketch the graphs for the volume of hydrogen gas against time for Experiments I, II and III using the same axes.

Activity 14

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0.2 g magnesium ribbon

Excess hydrochloric acid

Excess hydrochloric acid + copper(II) sulphate


1 The table below shows the volume of hydrogen gas released when 50.00 cm3 of sulphuric acid solution reacts with 5.0 g of granulated zinc.

Time/s 0 30 60 90 120 150 180 210Volume of hydrogen gas released/cm3

0.00 80.00 125.00 165.00 190.00 210.00 210.00 210.00

(a) Write the chemical equation for the reaction between zinc and sulphuric acid.

……………………………………………………………………………………………... [2 marks]

(b) Calculate the overall average rate of reaction of this experiment.

[1 mark](c) (i) Draw the graph of the volume of hydrogen gas released against time.

[4 marks]

(ii) From the graph , calculate the rate of reaction at the 80th seconds.

[2 marks](d) Instead of measuring the volume of hydrogen gas released, state another

method that can be used to calculate the rate of reaction in this experiment.

……………………………………………………………………………………………... [ 1 mark]

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WAJA F5 Chemistry 2010 Chapter 1 : Rate of Reaction2.

Based on the table and graph above, compare the rate of reaction between :(i) Experiment I and Experiment II(ii) Experiment II and Experiment III

Experiment I and Experiment II

The rate of reaction of experiment II is …………………………… compared to experiment I. The

temperature of experiment II is ………………………. The higher the temperature, the

……………………… the kinetic energy of the particles. The ………………………………… between

hydrogen ions, H+ and calsium carbonate happened. The frequency of collision ……………………. The

frequency of ……………………………… collision also increases. Hence, the rate of reaction

is……………………………….

Experiment II and Experiment III

The rate of reaction of experiment III is …………………………… compared to experiment II. The total

surface area of the reactants in experiment III is …………………………………………..

The ………………………………… between hydrogen ions, H+ and calsium carbonate happened. The

frequency of collision ……………………………. The frequency of ……………………………… collision

also increases. Hence, the rate of reaction …………………

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ANSWERActivity

1 speed , productreactants , products

2 1. S 2. S 3. F 4. S 5. F6. F 7. S 8. S 9. S 10. F

3 decrease , increase, increase, formingEq 1 : CaCO3 + 2HCl → CaCl2 + CO2 + H2OChanges : - decrease in the mass of CaCO3

- increase in volume of CO2 released

Eq 2 : Na2S2O3 + H2SO4 → Na2SO4 + SO2 + S + H2OChange : time taken for the yellow precipitate of sulphur formed

Eq 3 : 2H2O2 → 2H2O + O2

Change : increase in the volume of oxygen gas4 4A 2(a) V4 ; V2 ; V3 - V2 ; 60 ; V3 - V2

240 120 602(c) V2 - V1

160 - 30 4B 1 Plot a graph

2 (i) Average rate of reaction , V = 86 = 28.67 cm3min-1

in the first 3 min t 3(ii) V = V3 – V2 = 86 – 70 = 16 t = t3 – t2 = 3.0 – 2.0 = 1.0

Average rate of reaction , V = 16 = 16 cm3min-1

In the third min t 1.0

(iii) V = total volume of gas collected at 4.0 min (95 cm3) t = time taken for the reaction to be complete = 4.0 min Overall average rate of reaction , = V = 95 = 23.75 cm3min-1

t 4.0

(iv) Show a tangent at the 1 min of the graph The instantaneous rate of reaction at 1 min = gradient of the curve at 1 min = Y2 – Y1 = 70 – 30 = 40 = 26.67 cm3min-1

X2 – X1 1.55 – 0.5 1.55 1 (a) (i) Average rate of reaction in the first 10 sec

= 20 = 2 cm3 s-1

10(ii) Average rate of reaction in the first 30 sec

= 46 = 1.53 cm3 s-1 30

(iii) Overall average rate of reaction = 50 = 1.25 cm3 s-1

40(b) The rate of reaction decrease with time. (c) This is because the concentration of

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WAJA F5 Chemistry 2010 Chapter 1 : Rate of Reaction hydrochloric acid, HCl decreases. When there is no more hydrochloric acid, HCl remaining, the reaction is complete and the rate of reaction is zero.

2 (a) the first 60 seconds = 29 - 17 = 12 = 0.4 cm3s-1 60 - 30 30 (b) the overall reaction = 36 = 0.3 cm3s-1

1203 0.0036 g min-1

6 (a)(b)(c)(d)(e)

The size of solid reactant/ Total surface area of solid reactant TemperatureConcentration of reactantPresence of catalystPressure of gaseous reactant

7 12345678

√ TemperatureX√ Concentration√ Size of reactantX√ Presence of catalyst√ PressureX

8 (i) CaCO3 + 2HCl → CaCl2 + CO2 + H2O Steeper Higher Larger/bigger, higher

(ii) Na2S2O3 + 2HCl → 2NaCl + S + H2O + SO2. Shorter The rate of reaction Higher , higher

(iii) 2H2O2 → O2 + 2H2O Steeper Higher Increase

(iv) Na2S2O3 + 2HCl → 2NaCl + S + H2O + SO2. Shorter The rate of reaction Higher , higher

9 1 low (-30 – 10oC) , active , toxic , lower.high (25 – 40 oC) , more , lot of , higher

2 smaller , smaller , total surface area, higher3 (i) ammonia , N2 + 3H2 ↔ 2NH3 , 450 – 550oC , 200 – 400 atm, iron

(ii) contact , 2SO2 + O2 ↔ 2SO3 , 450 oC , 1 atm , vanadium(V) oxide10 1 (i) collision between particles

(ii) effective collisions(iii) activation energy

2 (i) collide(ii) product(iii) effective , activation energy

3 Minimum4 Reactant

11

21


Ea : Activation energyEa’ : Activation energy in the presence of catalyts

12 (i) total surface area , larger , increases , increase , higher (ii) lower , incrases , higher(iii) kinetic energy , faster , increase , more , increasing of , higher (iv) increase , number , increases , increases , higher

13 1

2

Volume of hydrogen gas /cm3

Volume of hydrogen gas /cm3

14 1

2

(a) Zn + H2SO4 → ZnSO4 + H2

(b) Overall average rate of reaction = 210 = ……………. cms-1

150(c) (i) (ii) [Draw a tangent at 80 s] [Rate of reaction = gradient of the tangent](d) The decreasing of the mass of zinc used.

(i) higher , higher , higher , collision , increases , effective , higher.(ii) higher , bigger.larger , collision, increases , effective , higher.

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ABC

15 5520

III II I

Time (s)

Time (s)

waja chp.1rate of reaction

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