Rate of chemical reactions

1.  The rate of chemical reactions can be affected
four factors
1. Concentrations
2. Contact area
3. Temperature
4. Present of catalyst
Author: Mr Lam

2. Chemical reaction between two chemicals
can be imagined as if boys and girls seeking
for their soulmates.
They are being very happy when they
find their better halves.
In this presentation, we are going to study
the ways of increasing the chance that
chemicals react with each other.

3. Low concentrations, particles are more difficult or at least more time to find
the right partners.

4.  Higher concentrations can increase the chance
that they meet each other, i.e. increase the
reaction rate

5. Only the ones in the middle are
in contact with the other
particles even the
concentrations are high

6. Break up the buck materials so that each will have more
chance to have the right partners around them, e.g. cut
calcium metals into smaller pieces before adding water

7. At low temperature, particles do not have much energy move
around and overcome some barriers. Even though they do meet
the ones they wants, they do not have enough resources to form a
relationship. (Think about having a girl friend does cost you a lot
of money and time. )

9.  Generally speaking, most of the chemical
reactions that happen in room temperature or
even a couple of hundreds degree Celsius:
 When the temperature increases by 10ᵒC, the reaction
rate doubles.
 In other word, if you increase the temperature by 30ᵒC,
the reaction rate will be 8 folds faster.
This “increase 10ᵒC in temperatre, reaction rate double” rule does not
applicable when the temperature is over 1000ᵒC, esp in metallurgical
reactions

10. Catalyst acts like a matchmaker. Imagine a
boy and a girl do not know how to start their
conversation, it would be much better to
have someone they know in common to start
the “ice-breaking” phrase. However, once
they start to react, the catalyst (matchmaker)
leaves and goes to help other couples.
Although the catalyst may change its
physical form after the reaction. For
example, a big piece of platinum (catalyst)
before the reaction can transform into
powder form after the reaction finishes.
Therefore, a catalyst does not involved in the
final products even through the catalyst
participates in the intermediate steps.

11. Another analogy is sewing. Sewing in
principle is to attach a thread to a piece
of cloth
Without the help of a needle, it is very or
almost impossible to sew.
However, after the thread is being
attached to cloth, there is no need to
leave the needle with the cloth or thread.
The needle is then removed and moves
on help other sewing jobs.
From this analogy, in a chemical reaction,
we do not need a lot of catalyst (same as
we do not need a lot of needles). A small
amount of catalyst can already do a lot of
sewing jobs.

12. Technically, in chemistry, we say catalyst lower the “activation
energy”. It is some sort of energy required to start a reaction. If
reactants do not have enough energy (e.g. heat) to overcome this
activation energy barrier, it cannot start a reaction and hence no
products. Catalyst is to lower this barrier. Therefore, with the help
of a catalyst, reactions can take place in a less strict condition.

13.  To increase a chemical reaction rate, we can
1. Increase the concentration
2. Increase the temperature
3. Increase contact area
4. Add catalyst