2. Contents
1. Understanding of Rate of Reaction
2. Factors Affecting Rate of Reaction
3. Collision Theory
4. Scientific Knowledge to Enhance Quality
of Life
3. 1.1 Understanding of Rate of
Reaction
Rate of reaction is defined as the change in the amount
of reactants or products per unit time.
We usually use water displacement method to collect
gas
5. •
•
•
•
•
The reaction is fastest at the start when the reactants are
at a maximum (steepest gradient)
The gradient becomes progressively less as reactants
are used up and the reaction slows down.
Finally the graph levels out when one of the reactants is
used up and the reaction stops.
The amount of product depends on the amount of
reactants used.
The initial rate of reaction is obtained by measuring the
gradient at the start of the reaction. A tangent line is
drawn to measure rate of reaction at instantaneous time.
6. Different chemical reactions occur at different rates.
• Fast Reaction
• Slow Reaction
Fast Reaction Slow Reaction
The time taken for a fast reaction is
short.
The time taken for a slow reaction is
long.
The rate of reaction is said to be
high.
The rate of reaction for a slow
reaction is low.
Example:
•Fading of dyes on a shirt under hot
sun
•Burning of petrol in a car engine
•Striking a match
•Ripening of tomatoes
Example:
•A piece of newspaper turning yellow
•The weathering of limestone by acid
rain
•Rusting of a water pipe
12. Example:
In a chemical reaction, 2.5g of calcium carbonate react
completely with excess hydrochloric acid to produce
600cm³ of carbon dioxide gas in 1.5 minutes. Find the rate
of reaction in term of
a. decreasing mass of calcium carbonate
b. increasing volume of carbon dioxide gas produced
13. Finding Average Rate Of Reaction
From Measurable
Quantities
During a chemical reaction, two things happen
1. The quantities of reactants reduce.
2. The quantities of products increase.
Therefore, the rate of the reaction can be determined by
• measuring the decrease of the amount of the reactants over
time.
measuring the increase of the amount of the products over time.
•
However, the quantity (or change) of the
reactants/product may be measurable or immeasurable.
The easily measured quantity changes include
•
•
•
Mass
Concentration (Conductivity)
Volume of gas
14.
15. Example:
In a reaction, 5 g of calcium carbonate
takes 250 seconds to completely react
with solution of hydrochloric acid.
Calculate the average rate for this
reaction in units
a)g s-1 and
b)mol s-1
[ Relative atomic mass: C 12; O, 16; Ca,
40]
17. Example:
When the aqueous of ethanadioic is
mixed with acided potassium
manganate(VII) , the reaction happen
slowly at room temperature. The
purple colour of the solution is
bleached after 20 seconds. Calculate
the average rate of reaction.
18. Analysing Rate of Reaction from
Graph
Graph Of Product/Reactant Change Against Time
Ina chemical reaction,
•
•
the reactants will decrease over time
the product will increase over time
the rate of reaction will decrease over time because of
the decrease in concentration and total surface area of
reactants.
Ina graph of quantity of product/reactant over time, the
rate of reaction is equal to the gradient of the graph.
19. Example:
The reaction between dilute hydrochloric acid and excess
marble will produce calcium chloride and gas of carbon
dioxide. Sketch the graph of
1. the mass of the marble against time.
2. the volume of carbon dioxide against time.
3. the concentration of hydrochloric acid against time.
4. the concentration of calcium chloride against time.
20.
21. Finding The Average Rate Of Reaction From A Graph
Example:
Inareactionbetweencalciumcarbonateandliquidhydrochloricacid,
carbondioxidegasthatisreleasediscollectedinaburette.The graph
showsthevolumeof carbondioxidecollectedovertime.Find the
averagerateof reactioninthefirst 60s.
22. Finding Instantaneous Rate Of Reaction From A Graph
The rate of reaction changes from time to time as the
reaction happens.
The rate of reaction at a particular time is called the
instantaneous rate.
The instantaneous rate of a reaction is equal to the
gradient of tangent at a particular time.
23. Example:
The graph shows the volume of carbon dioxide gas
released over time in a chemical reaction. Find the
rateof reactionatt= 40s
25. 1. Size of Solid Reactants/Total Surface Area
The smaller the size of the particle, the bigger
the total surface area.
The bigger the total surface area, the higher the
rate of reaction.
26. Experiment 1
25 cm3of 0.5 mol dm–3hydrochloric acid + calcium carbonate chips. The
carbon dioxide gas released is collected in a burrete. The volume of
the gas released is recorded in every 30s. The result is plotted in a
graph.
27. Experiment 2
25 cm3of 0.5 mol dm–3hydrochloric acid + calcium carbonate powder.
As in experiment 1, the carbon dioxide gas released is collected in a
burrete and the volume of the gas released is recorded in every 30s.
The result is plotted in the same graph in experiment 1.
28. Conclusion
• The gradient of the curve for experiment 2 is greater than the curve for
experiment 1. This indicate that the rate of reaction in experiment 2 is
higher than experiment 1.
• Conclusion: the smaller the particle size of the reactant, the bigger the
total surface area, and the bigger the total surface area, the higher the
rate of the reaction will be.
29. 2. Concentration Of
Reactants
Experiment
By measuring the time taken for the formation of sulphur
precipitate (yellow solid) when sulphuric acid, H2SO4reacts
with sodium thiosulphate(VI), Na2S2O3of different
concentration , we can investigate the effect of
concentration of the reactant on the rate of reaction.
The higher the concentration of the solution, the higher
the rate of reaction.
30. Procedure:
•50 cm3of 0.2 mol dm-3sodium thiosulphate solution + 10 cm3of 0.5 mol
dm-3sulphuric acid.
•
from view is recorded.
•The experiment is repeated by using sodium thiosulphate solution with
concentration 0.4 mol dm-3, 0.6 mol dm-3, 0.8 mol dm-3and 1.0 mol dm-3.
32. 3. Temperature Of The Reactant
Experiment
By measuring the time taken for the formation of sulphur
precipitate (yellow solid) when sulphuric acid, H2SO4reacts
with sodium thiosulphate(VI), Na2S2O3of different
temperature, we can investigate the effect of temperature
of the reactant on the rate of reaction.
Thehigherthetemperatureof the
solution,thehighertherateofreaction.
33. Procedure:
•50 cm3of 0.2 mol dm-3sodium thiosulphate solution at 30ºC + 10 cm3 of
0.5 mol dm-3sulphuric acid.
•
from view is recorded.
•The experiment is repeated by using sodium thiosulphate solution with
temperature 35ºC, 40ºC, 45ºC and 50ºC.
34. Conclusion :
• The graph for temperatureof sodium thiosulphate(VI),
Na2S2O3againsttimetakenforthesulphurprecipitatetoformed is
plotted.
• Asthetemperatureof sodiumthiosulphatesolutiondecreases, the
35. Pressure Of Gas
For reactions involve gas, the rate of reaction is affected
by the pressure of the gas.
Pressure DOES NOT affect the rate of reaction where
the reactants are in the form of solids or liquids.
The higher the pressure of the gas, the higher the rate of
reaction
The higher the pressure of the gas, the higher
the rate of reaction
36. 4. Catalyst
Catalyst
Only a small amount of catalyst is
needed to increases the rate of
reaction. An increase in the
quantity of catalyst will increase
the rate of reaction slightly
During a reaction, catalyst remains
chemically unchanged but may
undergo physical changes. For
example, catalyst may turn into
powder during the reaction
Change the rate of
reaction
Does not change the
quantity of products formed
Catalyst is a chemical substance that change the rate of
chemical reaction
Characteristics of catalyst:
It is specific in its action. It can
only catalyse a particular
reaction
38. List of Reactions and the Catalyst
Chemical Reaction Catalyst
Decomposition of hydrogen peroxide:
2H2O2 → 2H2O + O2
Manganese(IV) oxide, MnO2
Haber Process
N2 + 3H2 → 2NH3
Iron, Fe
Contact Process
2SO2 + O2 → 2SO3
Vanadium(V) oxide, V2O5
Ostwald Process
4NH3 + 5O2 → 4NO + 6H2O
Platinum, Pt
39. Factors Affecting
Catalyst
Acatalyst is a substance which can
change the rate of reaction.
There are 2 types of catalyst:
• Positive catalyst – Increase the rate of
reaction.
• Negative catalyst – Reduce the rate of
reaction.
42. Application of Catalysts in Industry
a) Haber Process (Produces Ammonia)
• In the Haber process, a mixture of nitrogen and hydrogen in
the ratio 1:3 is conducted through the powdered iron as
catalyst at a temperature of 450°- 550°C and a pressure of 200
-300 atmospheres.
Powdered iron is used as the catalyst to raise the rate of
reaction.
Also, the reaction is conducted at high temperature to increase
the rate of reaction.
•
•
43.
44.
45. 1.3 Collision Theory
The collision theory states
that:
•
•
• The particles of the reacting
need to touch to enable bond
formation or breaking to
happen.
Collisions of particles of a
reacting substance need to
achieve a certain minimum
energy (Activation Energy) in
order to produce a reaction.
Particles that collide also need
to have the correct orientation
of collision.
46. According to collision theory, atoms, ions, and molecules
can react to form products when they collide with one
another, provided that the colliding particles have
enough kinetic energy.
Effective Collision
Ineffective Collision
47. Activation Energy
• The minimum energy that the reactants particles must achieve at
the time of collision in order for a chemical reaction to take
place.
• The value of the activation energy is different for different
reactions.
• A reaction with high activation energy occurs slowly whereas a
reaction with a low activation energy occurs fast.
48. Energy Profile Diagram
In this diagram, the activation energy is shown by the difference in
energy between the peak of the graph and the level of the energy
of the reacting substance.
Exothermic Reaction Endothermic Reaction
49. Factors Affecting Rate Of
Reaction - Explanation By
Collision Theory
Total Surface Area of Reactants
• When the size of the solid substance that reacts is smaller, its total
surface area exposed becomes larger.
• This causes the collisions frequency between the reactants increases.
• As a result, the frequency of effective collisions also increases and
hence increases the rate of reaction.
50. Presence of Catalyst
• When a positive catalyst is used in a reaction, the catalyst
prepares an alternative path with lower activation energy for the
reaction.
• As a result, the frequency of effective collisions increases and
hence increases the rate of reaction.
51. Concentration
• Solution with higher concentration has more particles per unit
volume in the solution.
• As a result, the collisions frequency between the reactants
increases.
• Consequently, the frequency of effective collisions also
increases and hence the rate of reaction increases.
52. Temperature
•
• When the temperature of a reaction increases, the particles of
the reacting substances move faster.
This causes the collisions frequency between the reactants
increases.
• As a result, the frequency of effective collisions also increases
and hence increases the rate of reaction.
53. Pressure of Gas
•
•
• For a reaction that involves a gas, when pressure increases,
the particles of gas are compressed to fill the spaces which are
small. This makes the number of particles of gas per unit of
volume to increase.
This causes the collisions frequency between the reactants
increases.
As a result, the frequency of effective collisions also increases
and hence increases the rate of reaction
54. 1.4 Scientific Knowledge
to Enhance
Quality of Life
1. Keeping food in a refrigerator
• If food is kept in the fridge, the food will keep longer
because the low temperature will slow down the
rate of the chemical reaction which destroys food.
2. Cooking food in a pressure cooker
•
• In a pressure cooker, the high pressure causes the
water in the cooker to boil at a temperature of more
than 100°C.
At a higher temperature, the time for the food to get
cooked is decreased.
55. 3. Cooking Food in Small Pieces
Vegetable oil is an organic compound that is not
saturated and exists in liquid state at room
temperature.
Vegetable oil can be changed to margarine through
the process of hydrogenation using nickel as catalyst
at a temperature of 180°C
• Food in the shape of big pieces has a surface area
per volume which is small, so the heat takes a longer
time to reach the inside of the food. So, to cook
faster, the food needs to be cut into smaller pieces.
4. Making Margarine
•
56. 5. Burning of Coal
• Coal contains the element carbon.
• A big piece of coal takes a long time to burn because the total
surface area that is touched by the fire is small.
• The rate of burning pieces of coal which are small is higher
because the total surface area is bigger. With this, it provides a
lot of heat energy in a short period of time.
