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Answers to Practise Questions (Basic) – Rate of Reaction
Practise questions (Basic) are designed to ensure that students are aware of the basic
concepts of the topic. This should be the first step that students undertake while
revising for their chemistry examination. For the O Level examination, these basic
concepts will be tested although questions will not be straight forward and students
will need to be able to apply these concepts to solve the questions.
(1): Explain why increasing the (i) concentration (ii) temperature of reacting
particles increases the rate of reaction.
Increasing the concentration increases the number of reacting particles per unit
volume. This increases the number of collisions between reacting particles. As a
result, the number of effective collisions increases. Thus, rate of reaction increases
with increasing concentration.
When the temperature is increased, the reacting particles have more energy and
move faster. They collide more frequently and with energy greater than the activation
energy. This increases the number of effective collision. Thus, rate of reaction
increases when the temperature is increased.
(2): Explain why decreasing the particle size of the reactants increases the rate of
reaction.
When the particle size is decreased, there is an increased surface area exposed to
collision with other reactants. Thus, the number of collisions and effective collisions
between reacting particles increase. This increases the rate of reaction.
(3): Explain why the usage of catalyst increases the rate of reaction.
The usage of catalyst decreases the activation energy of the reaction. As a result, there
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are more reacting particles with energy greater than the activation energy. Thus, the
frequency of effective collisions increase. This increases the rate of reaction.
(4): State whether addition of catalyst increases the amount of energy release during
a chemical reaction.
Catalyst does not alter the enthalpy change of a chemical reaction.
(5): Describe briefly how the rate the below reactions could be monitored:
(a): Calcium carbonate with hydrochloric acid
Carbon dioxide is produced during the reaction. The mass of the reacting mixture
could be monitored during the reaction. As carbon dioxide is released during the
reaction, the mass of the reacting mixture would decrease. By monitoring, the change
in mass of the reacting mixture, the rate of reaction could be monitored.
(b): Sodium thiosulfate with hydrochloric acid producing sodium chloride, water,
sulfur dioxide and sulfur
Sulfur is produced during the reaction and this could produce a suspension which
could make the flask opaque when view from the top. By monitoring the time taken
for the view to be blocked, the rate of reaction could be monitored.
(c): Decomposition of hydrogen peroxide producing water and oxygen gas
As oxygen gas is produced during the reaction; the reaction could be monitored by
measuring the volume of gas that is released.
(6): Give two examples of catalysts and their uses in industry
Iron is used in the production of ammonia in the Haber process
Nickel is used in the addition reaction of alkene producing alkane
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About Breeze Education:
Breeze Education offers chemistry tuition to O Level Students. Tuition classes are
conducted in small group to facilitate active discussion and consultation. Chemistry is
taught in a way to facilitate easy understanding of the topic. Students are also honed
on their revision techniques so that they can improve faster over a shorter period of
time. Tuition sessions are planned and taught by Dr Francis who has a PhD in
Biomedical Science from National University of Singapore. Lesson is conducted in
Yishun with direct bus connecting to Sembawang and Woodlands.
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