DK014

DETERMINATION THE ORDER OF REACTION BY INITIAL RATE METHOD

1. Use concentration measurement to find initial rate.
2. Use initial rates from several experiments to find reaction orders.
3. Use these values to calculate rate constant.

EXAMPLE 8
Determine the rate law and calculate the rate constant for the following reaction from the
following data:

F2 (g) + 2ClO2 (g) → 2FClO2 (g)

Experiment [F2] M [ClO2] M Initial Rate (M/s)
1 0.10 0.010 1.2 x 10-3
2 0.10 0.040 4.8 x 10-3
3 0.20 0.010 2.4 x 10-3

Solution

We assume that the rate law has the following form:

Rate = k[F2]x[ClO2]y

Find order in F2 with [ClO2] constant (Use experiment 1 and 3):

Rate 3 = k[F2]x[ClO2]y 2.4 X 10-3 Ms-1 = k (0.20 M)x (0.010)y
Rate 1 = k[F2]x[ClO2]y 1.2 X 10-3Ms-1 k (0.10 M)x (0.010)y

2.4 X 10-3 = (0.20)x
1.2 X 10-3 (0.10)x

(2.0)1 = (2.0)x

x = 1 (first order with respect to F2)

Find order in ClO2 with [F2] constant (Use experiment 1 and 2):

Rate 2 = k[F2]x[ClO2]y 4.8 X 10-3 Ms-1 = k (0.10 M)x (0.040)y
Rate 1 = k[F2]x[ClO2]y 1.2 X 10-3Ms-1 k (0.10 M)x (0.010)y

4.8 X 10-3 = (0.040)y
1.2 X 10-3 (0.010)y

(4.0)1 = (4.0)y

y = 1 (first order with respect to ClO2)

Thus, rate law:
rate = k[F2][ClO2]

Use any experiment data (example Exp. 1) to find k

1.2 x 10-3 M s–1 = k(0.1 M) (0.01 M)
k = 1.2 M–1s–1

147 | Chapter 9 Chemistry 1 DK014

EXERCISE 6
In the combustion of hexane:

2C6H14(g) + 19O2(g) → 12CO2(g) + 14H2O(g)

It was found that the rate of reaction of C6H14 was 1.20 molL–1s–1.

(a) What was the rate of reaction of O2?
(b) What was the rate of formation of CO2?
(c) What was the rate of formation of H2O?

Answer:
(a) 11.4 molL–1s–1
(b) 7.20 molL–1s–1
(c) 8.40 molL–1s–1

EXERCISE 7

The rate law for decomposition of HI to I2 and H2 is

Rate = k[HI]2

At 508oC, the rate of the reaction of HI was found to 2.5 x 10–4 molL–1s–1 when the HI
concentration was 0.0558 M. What the value of k?

Answer:
0.080 M–1s–1

EXERCISE 8

Consider the reaction between nitrogen dioxide, NO and carbon monoxide, CO :
NO2(g) + CO(g) → NO(g) + CO2(g)

The initial rate of the reaction is measured at several different concentrations of the
reactants with the following results :

Experiment [ NO2 ] / M [ CO ] / M Initial rate (Ms-1)

1 0.10 0.10 0.0021

2 0.20 0.10 0.0082

3 0.20 0.20 0.0083

4 0.40 0.10 0.033

From the data, determine the rate law and rate constant for the reaction.

Answer:
rate = k[NO2]2[CO]0
k = 0.21 M–1s–1

148 | Chapter 9 Chemistry 1 DK014

EXERCISE 9
The reaction of iodide ion with hypochlorite ion, OCl– (the active ingredient in a “chlorine
bleach” such as Clorox), follow the equation:

OCl–(aq) + I–(aq) → OI–(aq) + Cl–(aq).

It is a rapid reaction that give the following data:

Exp. Initial [OCl–] Initial [I–] Initial Rate
1 (mol/L) (mol/L) (molL–1s–1)
1.7 x 10–3
1.7 x 10–3 1.75 x 104

2 3.4 x 10–3 1.7 x 10–3 3.50 x 104

3 1.7 x 10–3 3.4 x 10–3 3.50 x 104

What is the rate law for the reaction? Determine the value of reaction constant with it

correct unit.

Answer:
rate = k[OCl–][I–]
k = 6.1 x 109 molL–1s–1

9.2 FACTOR AFFECTING REACTION RATE

On a molecular level, reaction rates depend on the frequency of the collisions between
molecules. The greater the frequency of collisions, the higher the reaction rates. The
The collision theory (based on the kinetic-molecular theory), state that:

i. Molecules of reactants must collide in order to form products.
ii. Products are formed only when effective collisions occur between molecules.

Effective collision is a collision in which the particle meet with sufficient energy and an
orientation that allow them to react. So, effective collisions require the followings :

i. The colliding molecules must have a total kinetic energy equal to or greater than
the activation energy, Ea.

ii. Collisions occur at the correct orientation.

ACTIVATION ENERGY (Ea)

The activation energy, Ea is the minimum energy required to initiate a chemical
reaction. In 1888, the Swedish chemist Svante Arrhenius, suggested that molecules must
possess a certain minumum energy to react. According to the collision theory, this energy
comes from the kinetic energies of the colliding molecules. Upon collision, the kinetic energy
of the molecules can be used to stretch, bend, and ultimately break bonds, leading to the
chemical reactions and will form new bonds in the product. That is, the kinetics energy is
used to change the potential energy of the molecule. If molecules are moving too slow, in
other words, with too little kinetics energy, they merely bounce off one another without
changing. So, the minimum energy required to initiate a chemical reaction is called Ea, and
its value varies from reaction to reaction.

149 | Chapter 9 Chemistry 1 DK014

THE ORIENTATION OF COLLISIONS
In most reactions, collision between molecules results in chemical reaction only if the
molecules are oriented in a certan way when they collide. The correct orientation means
that the collision of molecules occur at the correct angle that favors the formation of products.
For example,

Cl + NOCl → NO + Cl2

The reaction which take place if the collision brings Cl atom together to form Cl2 as shown
in top diagram. In contrast, in the collision show in lower diagram, the two Cl atoms are not
colliding directly with another, and no product form.

FACTOR AFFECTING REACTION RATE
Under any given set of condition, each reaction has its own characteristic rate, which is
determined by chemical nature of the reactants. So, there are four(4) factors can affect the
rate at which any particular reaction occurs.
i. Concentration or Pressure.
Most chemical reaction proceed more quickly if the concentration of one or more reactant is
increased. As concentration of reactant increases, the number of quantity of reactants
increase , the number of collisions between particles also increases. So, the frequency

150 | Chapter 9 Chemistry 1 DK014

of effective collision increases leading to increased the rate of reaction. For example,
steel wools burn slowly in air which contain 20% of O2, but burst into flame in pure oxygen.
For gasses reactant, if pressure increased (reducing the volume of the container),
concentration of reactant increases, the number of molecule per unit volume of reactants
increase , the number of collisions between particles also increases. So, the frequency of
effective collision increases leading to increased the rate of reaction.

ii. Temperature
Reaction rate generally increase as temperature increase. The effect of temperature on
the reaction rate can be explained in terms of kinetic theory. Increasing the temperature
increases the kinetic energies of molecules. The number of molecules with energy
equal or greater than Ea also increase. As molecules move rapidly, they collide more
frequently and with higher energy, so the effective collision also increase, leading to
increased the rate of reaction. For example, the bacterial reactions spoil milk, for instance,
proceed more rapidly at room temperature than at lower temperature of a refrigerator.

iii. Particle Size
Reactant must come together to react. The more readily react molecules collide with one
another, the more rapidly they react. A reaction is limited by the area of contact of the
reactants.The reaction that involve solids tend to proceed more rapidly if the surface area of
the solid increased. When the size of reacting particles decrease, total surface area
exposed for reaction increases. The number of collisions between particles increases.
So, frequency of effective collisions increases, leading to the increased the rate of
reaction. For example, a medicine in the form of fine powder, dissolves in the stomach and
enter the blood quickly than the same medicine in the form of tablet.

151 | Chapter 9 Chemistry 1 DK014

iv. Catalyst
Catalyst are agents that increase reaction rates without themselves being used up. A
catalyst provides an alternative pathway which has a lower activation energy compared to
the one without catalyst. For example, the uses of MnO2 in the decomposition of H2O2 will
make the process become faster.

152 | Chapter 9 Chemistry 1 DK014

TUTORIAL 9

SECTION A
1. The rate of a chemical reaction can be expressed in

A. Grams per mole
B. Energy consumed per mole
C. Volume of gas per unit time
D. Molarity per second

2. Which of these is not a sign that a chemical reaction has taken place?
A. Changing size
B. Changing color
C. A gas being formed
D. Formation of a precipitate

3. The rate law for a reaction is k [A][B]2 .Which one of the following statements is false?
A. The reaction is first order in A
B. The reaction is second order in B
C. The reaction is second order overall
D. k is the reaction rate constant

4. For a reaction 2A + B → 2C, with the rate equation: Rate = k[A]2[B]
A. The order with respect to A is 1 and the order overall is 1
B. The order with respect to A is 2 and the order overall is 3
C. The order with respect to B is 2 and the order overall is 2
D. The order with respect to B is 2 and the order overall is 3

5. The rate of a reaction depends on __________. C. Collision orientation
A. Collision frequency D. All of the above
B. Collision energy

6. The rate law of the overall reaction is k [A][B]0. Which of the following will not increase the
rate of the reaction?

A. Increasing the concentration of reactant A
B. Increasing the concentration of reactant B
C. Increasing the temperature of the reaction
D. Adding a catalyst for the reaction

153 | Chapter 9 Chemistry 1 DK014

7. Crushing a solid into a powder will increase reaction rate because:

A. the particles will collide with more energy
B. the orientation of colliding particles will be improved
C. the activation energy barrier will be lowered
D. the powdered form has more surface area

8. When the concentration of reactant molecules is increased, the rate of reaction increases.
The best explanation is: As the reactant concentration increases,

A. The average kinetic energy of molecules increases
B. The frequency of molecular collisions increases
C. The rate constant increases
D. The activation energy increases

9. Which one of the following statements concerning rates of reactions is FALSE?
A. The higher the activation energy barrier, the faster the reaction
B. Increasing the concentration of a reactant may increase the rate of a reaction
C. Adding a catalyst speeds up the rate of reaction for both the forward and reverse
reactions
D. Increasing the concentration increases the rate of a reaction, because it increases
the number of collisions

10. The rate of reaction that does not involve gases is not dependent on:
A. Pressure
B. Temperature
C. Concentration
D. Catalyst

SECTION B
1. Define the following term.

(a) rate of reaction:
(b) rate law
(c) rate constant
(d) activation energy

2. A study of the rate of the reaction represented as 2A⟶B gave the following data:

Time (s) 0.0 5.0 10.0 15.0 20.0 25.0 30.0

[A] (M) 1.00 0.952 0.625 0.465 0.370 0.308 0.230

154 | Chapter 9 Chemistry 1 DK014

By plotting a graph;
(a) Determine the average rate of disappearance of A between 0.0 s and 10.0 s, and

between 10.0 s and 20.0 s.
(b) Estimate the instantaneous rate of disappearance of A at 15.0 s from a graph of

time versus [A]. What are the units of this rate?
(c) Use the rates found in parts (a) and (b) to determine the average rate of formation

of B between 0.00 s and 10.0 s, and the instantaneous rate of formation of B at
15.0 s.

3. Write the differential rate equation for the following reactions.
i. I-(aq) + OCl-(aq) → Cl-(aq) + OI-(aq)
ii. 3O2(g) → 2O3(g)
iii. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)

[ ]
4. For the reaction: A + 2B → C + 2D, the reaction rate, − is 2.610−2 M s−1. What is

[ ]
the value for reaction rate of − ?

5. Consider the reaction:
N2(g) + 3H2(g) → 2NH3(g)

Suppose that at a particular moment during the reaction, molecule of hydrogen is
reacting at the rate of 0.074 M s–1. Calculate the rate of

(a) Formation of ammonia.
(b) Depletion of nitrogen.

6. The reaction A + 2B → products was found to have the rate law, rate = k [A] [B]2. Predict
by what factor the rate of reaction will increase when the concentration of B is doubled
and the concentration of A remained unchanged.

7. The reaction of nitric oxide with hydrogen at 1280C is

2NO(g) + 2H2(g) → N2(g) + 2H2O(l)

The following data was collected at this temperature :

Experimen [NO]/M [H2]/M Initial rate /Ms−1
t
1.25×10−5
1 5.00×10−3 2.00×10−3 5.00×10−5
10.00×10−5
2 10.00×10−3 2.00×10−3

3 10.00×10−3 4.00×10−3

155 | Chapter 9 Chemistry 1 DK014

Based on the data, determine

(a) The rate law.
(b) The rate constant.

8. The data below were obtained from the following reaction at 27oC .

CH3CH(Cl)CH3 + NaOH→ CH3CH(OH)CH3 + NaCl

Exp. [CH3CH(Cl)CH3]/M [NaOH]/M Reaction rate
1 0.15 0.25 (M min−1)
3.0×10−3

2 0.15 0.50 6.0×10−3

3 0.45 0.25 9.0×10−3

(a) What is the order with respect to each reactant?
(b) Write the rate equation.

9. The following data were measured for the reaction:

2NO(g) + Cl2(g) → 2NOCl(g)

Reaction rate Concentration (mol dm−3)
(mol dm−3 hr −1) NO Cl2
0.50 0.50
1.19

4.79 1.00 0.50

9.59 1.00 1.00

Write the rate law for the reaction.

10 The following equation shows the decomposition of HI(g):

. Pt ΔH = -ve
2HI(g) H2(g) + I2(g)

(a) What is the function of platinum?

(b) Give another two factors that can influence the reaction rate and explain your
answer.

Revised by,
Farhana Binti Umanan
Zanarina Binti Sapiai

156 | Chapter 9 Chemistry 1 DK014

DK014
Pre-Lab Module

EXPERIMENT 1
DETERMINATION OF THE DENSITY OF WATER

Course Learning Outcome:

Solve chemistry related problems by applying basic concepts and principles in physical and
organic chemistry. (C3, PLO4, CTPS2, MQF LOD6)

Learning Outcomes:

At the end of this lesson, students should be able to :
1. chose the correct apparatus to determine the density of water
2. calculate the density of water
3. compare the accuracy of the density of water using different apparatus

Student Learning Time:

Face-to-face Non face-to-face
1 hour 1 hour

Direction: Read over the lab manual and then answer the following question.

Introduction:
1. Define density.

2. Give one example of the unit of density.

3. What is the density of water at 25oC.

Procedure
1. List down the apparatus in laboratory that possible to be used to measure volume of

water.

157 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

DK014
Pre-Lab Module

2. Suggest the procedure to determine the density of water by using different apparatus to
measure a volume of water in laboratory

Experiment 1 : Data Analysis

1. A group of students carried out an experiment how to determine the density of 10 mL
water using different apparatus and the data is shown in the table below. Calculate
the density of water.

Data Burette Pipette Measuring
cylinder
Mass of empty beaker / g 21.4125 21.3455 21.3831
Mass of beaker + water / g 31.2535 31.3377
Mass of water transferred / g 31.0141
Density of water / g mL-1

2. Compare the accuracy of apparatus to measure the volume by using the density of
water value.

158 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

DK014
Pre-Lab Module

EXPERIMENT 2
STANDARD SOLUTION AND DETERMINING
OF THE CONCENTRATION OF ACID SOLUTION.

Course Learning Outcome:

Solve chemistry related problems by applying basic concepts and principles in physical and
organic chemistry. (C3, PLO4, CTPS2, MQF LOD6)

Learning Outcomes:

At the end of this lesson, students should be able to :

1. define molarity and standard solution
2. state the use of standard solution
3. describe the preparation of a standard solution of sodium carbonate, Na2CO3.
4. calculate the concentration of HCl solution in an acid-base titration

Student Learning Time:

Face-to-face Non face-to-face
1 hour 1 hour

Direction: Read over the lab manual and then answer the following question.

Introduction:
1. Define molarity.

2. What is a standard solution and give the use of a standard solution

Procedure

1. What is the possible error that might be occur during preparation of a standard
solution by using volumetric flask and State the precaution step to avoid the error
mentioned .

159 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

DK014
Pre-Lab Module

2. What are the decimal places for burette reading? If the burette is fully filled, what is
the initial reading?

3. State three precautions that must be taken during titration to ensure the accuracy of
the results.

160 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

DK014
Pre-Lab Module

Experiment 2 : Data Analysis

1. The data for a titration of HCl solution with KOH solution are as follows:

Volume of HCl used 25.0mL
Initial burette reading 0.50mL
Final burette reading
Concentration of KOH 25.60mL
1.0M

a. State the titrant and analyte respectively

b. Calculate the volume of KOH dispensed.

c. Calculate the number of mole of KOH

d. Write the balance equation for the neutralisation reaction.
e. Write the stoichiometric relation between KOH and HCl.
f. Calculate the molarity of HCl solution.

161 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

DK014
Pre-Lab Module

EXPERIMENT 3
QUANTITATIVE ANALYSIS OF BAKING SODA

Course Learning Outcome:

Solve chemistry related problems by applying basic concepts and principles in physical and
organic chemistry. (C3, PLO4, CTPS2, MQF LOD6)

Learning Outcomes:

At the end of this lesson, students should be able to :

1. determine mass of a solution by using volume data and density.
2. calculate the percentage by mass of NaHCO3 in baking soda

Student Learning Time:

Face-to-face Non face-to-face
1 hour 1 hour

Direction: Read over the lab manual and then answer the following question.

Introduction:
1. Define percentage by mass.

2. What is the use of density in the calculation of percentage by mass?

Procedure
1. What is the standard solution used in this experiment?

2. What is the indicator used in this experiment? State the colour change when the
endpoint during the titration.

162 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

DK014
Pre-Lab Module

3. Why the gross reading is needed when doing the titration?
4. State two precautions that must be taken during titration to ensure the accuracy

of the results.

Experiment 3 : Data Analysis
1. A 100 mL aqueous solution of NaOH with density of 1.515 gmL-1 at 20° C was
prepared by adding 3.8 g solid NaOH.
i. Calculate the mass of NaOH solution.

ii. Calculate the percentage by mass of NaOH solution

163 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

DK014
Pre-Lab Module

EXPERIMENT 4
MOLECULAR GEOMETRY

Course Learning Outcome:

Solve chemistry related problems by applying basic concepts and principles in physical and
organic chemistry. (C3, PLO4, CTPS2, MQF LOD6)

Learning Outcomes:

At the end of this lesson, students should be able to :

1. draw the Lewis structure of a molecules and polyatomic ions
2. apply VSEPR theory to determine the molecular shape.
3. draw the basic molecular geometry of the molecules and polyatomic ions

Student Learning Time:

Face-to-face Non face-to-face
1 hour 1 hour

Direction: Read over the lab manual and then answer the following question.

Introduction
1. Write the steps how to draw a Lewis structure

2. What is the abbreviation of VSEPR stand for?
3. List down the general formula of the 5 basic shape.

164 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

DK014
Pre-Lab Module

Procedure
1. Draw the Lewis structure of the following molecules.

MOLECULE LEWIS STRUCTURE
BeCl2

AlCl3

CCl4

PCl5

Experiment 4 : Data Analysis

1. Draw the basic shape and its bond angle for the following molecules.

MOLECULE MOLECULAR BOND ANGLE GENERAL
GEOMETRY FORMULA

BeCl2

AlCl3

CCl4

PCl5

165 | P r e - L a b C h e m i s t r y 1 D K 0 1 4

©chemistryunitkmkt2021