INTRODUCTION
Chemical kinetics is defined as the study of chemical reactions in terms of their
reaction rates and the various factors that affect them. The rate at which the reaction
occurs can be altered by changing the set of conditions such as: temperature,
concentration, pressure, surface area and the use of catalysts (Lister and Renshaw,
2008). Simple collision theory highlights the way in which these factors affect the
reaction rate on a molecular level. In order for a reaction to occur, the particles must
collide with sufficient energy to break bonds and must also be in the correct
orientation. The collision must take place between the area of the molecule that is
going to react together especially with unsymmetrical species as repulsion may cause
molecules to bounce off each other. Moreover, even with the correct orientation a
reaction cannot occur unless the reactant particles collide with the minimum energy
called the activation energy (Ea). The activation energy is the barrier in which a
reaction can take place and so only those collisions which have energies equal to or
greater than the activation energy can result in a reaction. Therefore, the rate of rate of
reaction is dependent upon the rate of successful collisions between the reactant
particles (The Editors of Encyclopædia Britannica, 1998). Altering certain factors
affecting reaction rates will determine the speed of a chemical reaction. For instance,
by increasing the temperature of the reaction the kinetic energy of the particles also
increases and so a greater proportion of colliding particles will have the sufficient
energy to overcome the activation energy and react. By studying the kinetics of a
reaction, chemists gain insights into how to control reaction conditions to achieve a
desired outcome.
OBJECTIVES
1. To determine how the concentration of a species can affect reaction rate in the
determination of rate law and rate constant.
2. To determine how temperature affects reaction rate.
APPARATUS

Stopwatch

250 mL conical flask

Burette

Pipette
CHEMICALS

0.20M

0.0050M

0.10M
Potassium Iodide (KI Solution)
Sodium Thiosulfate (Na₂S₂O₃ containing 0.4% starch indicator)
Potassium Peroxydisulfate
PROCEDURE
Part I: Finding The Rate Law And Rate Constant
1. The most accurate glassware that allows for variable volumes to be dispensed for
all volume additions was used. The experiment was planned well and carried out in
pairs. Trial 1 to 4 was done by one person while the others have done Trial 1,5 to 7.
2. The solution for each trial was prepared based on the volume as stated in Table 3.1
3. The first solution that was made was a solution containing the iodide (I⁻),
thiosulfate (S₂O₃²⁻) and any water (H₂O) needed since we must time the reaction. The
peroxydisulfate (S₂O₈²⁻) was then added. The timing was soon began as the
peroxydisulfate was added and the reaction was immediately swirled to ensure good
mixing. The timing was stopped when the solution changed to blue.
4. The trials was performed at least two runs for each trials, or until the reproductible
reaction times was obtained. The concentration of KI and K₂S₂O₈ are such that a
stoichiometric mixture for Reaction (Eq. 2) would result from equal volumes.
5. We used a constant total volume of 50.00 mL in a 250 mL conical flask to ensure
uniform conditions for all runs. In addition, the initial [S₂O₃²⁻]₀ = 0.0010 M for each
run was maintained.
Table 3.1: Volume Used For The Preparation Of Each Trial
Trial
Volume I⁻
(ml)
Volume
S₂O₃²⁻ (mL)
Volume
H₂O (mL)
Volume
S₂O₈²⁻ (mL)
1
2
3
4
5
6
7
20
15
10
5
20
20
20
10
10
10
10
10
10
10
0
5
10
15
5
10
15
20
20
20
20
15
10
5
Total
Volume
(mL)
50
50
50
50
50
50
50
6. Trial 1 serves as a reference reaction mixture - it has the stoichiometric amount of
each reactant.
Part II: Temperature Dependence Of The Rate Constant
1. The reference reaction mixture was used in this run. The mixture containing
I⁻-S₂O₃²⁻ was warmed using a hotplate or cooled using an ice bath before adding the
peroxydisulfate.
2. The timing was begun as soon as the peroxydisulfate (S₂O₈²⁻) was added and the
reaction was swirled immediately to ensure good mixing. The temperature was
recorded just after timing the reaction. The timing was stopped when the solution
changes to blue.
3. The non ambient temperature was done at least for two runs. The boiling or very
high temperature was avoided since the I₂⁻ starch complex becomes unstable and
difficult to form in high temperature.
RESULT
Part I : Finding the rate law and rate constant
Trial
1
2
3
4
Temperature of the experiment: 27°C
Volume Volume Volume Volume
I-(mL)
S2
O82- S2O32H2O
(mL)
(mL)
(mL)
Total
volume
(mL)
20
20
10
0
50
15
20
10
5
50
10
20
10
10
5
20
10
15
[I-] Time
(mol) (Run
1)
Time
(Run2)
Time
AVE
Rate
(mol/s
-1
)
5.14
7.16
6.15
0.03
0.2
6.52
8.54
7.53
0.03
50
0.2
10.38
11.11
10.75
0.02
50
0.2
11.35
16.85
14.1
0.01
0.2
2.Varying the concentration of [S2 O82- ] and keeping [I-] constant
Volume Volume Volume Volume Total
Trial I-(mL)
S2 O82S2O32H2O
volume
(mL)
(mL)
(mL)
(mL)
[S2O82-]
(mol)
Time
Time
(Run 1) (Run 2)
Time
AVE
Rate
(mol/s-1
)
1
20
20
10
0
50
0.1
5.14
5.19
5.17
0.02
5
20
15
10
5
50
0.1
6.39
6.41
6.4
0.02
6
20
10
10
10
50
0.1
9.30
9.74
9.52
0.01
7
20
5
10
15
50
0.1
16.25
16.37
16.31
0.006
Part II: Temperature dependence of the rate constant
Volume
I-(mL)
Volume
S2 O82(mL)
Volume
S2O32(mL)
Volume
H2O (mL)
Total
volume
(mL)
Temp,
T
(°C)
Time
(s)
Rate
(°Cs-1)
1
(ambient T)
20
20
10
0
50
22
40
0.55
2
(non ambient
T)
20
20
10
0
50
10
30
0.33
3
(non ambient
T)
20
20
10
0
50
55
15
3.67
Trial
1. Varying the concentration of [ Iˉ ] and keeping [ S₂O₈²ˉ ] constant
- The slope of the graph showing that as the concentration of iodide increases,the rate
of reacion increases too.
2. Varying the concentration of [S₂O₈²ˉ] and keeping [Iˉ] constant.
- The slope of the graph showing that as the concentration of [S₂O₈²ˉ] increases,the rate
of reaction increases too.
DISCUSSIONS
1. Describe the rate of reaction.
a.
Part Ⅰ
After potassium iodide, KI is added with sodium thiosulfate, Na₂S₂O₃ and
water, H₂O (except trial 1) in a conical flask, potassium peroxydisulfate, K₂S₂O₈
will be added by using burette and the colour of the solution from white will turn
to yellowish and at last brown after a period of time.
b.
Part ⅠⅠ
Potassium iodide, KI is added with sodium thiosulfate, Na₂S₂O₃ in a conical
flask and the solution was warmed or cooled until it reach the specific temperature.
After the solution reached the specific temperature, potassium peroxydisulfate will
be added to the solution and it will be heat or cool again until the white colour of
the solution turns to yellow and at last brown after a period of time.
2. What is the function of potassium peroxydisulfate, K₂S₂O₈?
Peroxydisulfate ion in potassium peroxydisulfate is a powerful oxidising agent but the
reaction will be slow at room temperature in the absence of catalyst.
3. What is the relationship between the temperature of the solution and the rate of
reaction?
Rate of reaction increases when the temperature increases.
QUESTION
No question in manual.
CONCLUSION
When the volume of iodide is low and the volume of water is high, the concentration
of the solution decrease thus the rate of reaction is low. When the temperature of
solution increases, the rate of reaction increases
REFERENCE
1. https://www.studocu.com/en-gb/document/university-of-sussex/introductory-chem
istry-for-biosciences-foundation-year/essays/lab-report-on-rate-of-reaction/1546141/v
iew
2. https://ocw.mit.edu/courses/chemistry/5-302-introduction-to-experi
mental-chemistry-january-iap-2005/labs/3_kinetics_2005b.pdf
3.https://www.chemguide.co.uk/physical/basicrates/temperature.html