# 3.1 Collision theory, measurement and mechanism  (Page 3/4)

 Page 3 / 4

## Experiment : measuring reaction rates

Aim:

To measure the effect of concentration on the rate of a reaction.

Apparatus:

• 300 cm ${}^{3}$ of sodium thiosulphate (Na ${}_{2}$ S ${}_{2}$ O ${}_{3}$ ) solution. Prepare a solution of sodium thiosulphate by adding 12 g of Na ${}_{2}$ S ${}_{2}$ O ${}_{3}$ to 300 cm ${}^{3}$ of water. This is solution 'A'.
• 300 cm ${}^{3}$ of water
• 100 cm ${}^{3}$ of 1:10 dilute hydrochloric acid. This is solution 'B'.
• Six 100 cm ${}^{3}$ glass beakers
• Measuring cylinders
• Paper and marking pen
• Stopwatch or timer

Method:

One way to measure the rate of this reaction is to place a piece of paper with a cross underneath the reaction beaker to see how quickly the cross is made invisible by the formation of the sulfur precipitate.

1. Set up six beakers on a flat surface and mark them from 1 to 6. Under each beaker you will need to place a piece of paper with a large black cross.
2. Pour 60 cm ${}^{3}$ solution A into the first beaker and add 20 cm ${}^{3}$ of water
3. Use the measuring cylinder to measure 10 cm ${}^{3}$ HCl. Now add this HCl to the solution that is already in the first beaker (NB: Make sure that you always clean out the measuring cylinder you have used before using it for another chemical).
4. Using a stopwatch with seconds, record the time it takes for the precipitate that forms to block out the cross.
5. Now measure 50 cm ${}^{3}$ of solution A into the second beaker and add 30 cm ${}^{3}$ of water. To this second beaker, add 10 cm ${}^{3}$ HCl, time the reaction and record the results as you did before.
6. Continue the experiment by diluting solution A as shown below.
 Beaker Solution A (cm ${}^{3}$ ) Water (cm ${}^{3}$ ) Solution B (cm ${}^{3}$ ) Time (s) 1 60 20 10 2 50 30 10 3 40 40 10 4 30 50 10 5 20 60 10 6 10 70 10

The equation for the reaction between sodium thiosulphate and hydrochloric acid is:

$N{a}_{2}{S}_{2}{O}_{3}\left(aq\right)+2HCl\left(aq\right)\to 2NaCl\left(aq\right)+S{O}_{2}\left(aq\right)+{H}_{2}O\left(l\right)+S\left(s\right)$

Results:

• Calculate the reaction rate in each beaker. This can be done using the following equation:
$Rate\phantom{\rule{4pt}{0ex}}of\phantom{\rule{4pt}{0ex}}reaction=\frac{1}{time}$
• Represent your results on a graph. Concentration will be on the x-axis and reaction rate on the y-axis. Note that the original volume of Na ${}_{2}$ S ${}_{2}$ O ${}_{3}$ can be used as a measure of concentration.
• Why was it important to keep the volume of HCl constant?
• Describe the relationship between concentration and reaction rate.

Conclusions:

The rate of the reaction is fastest when the concentration of the reactants was the highest.

## Mechanism of reaction and catalysis

Earlier it was mentioned that it is the collision of particles that causes reactions to occur and that only some of these collisions are 'successful'. This is because the reactant particles have a wide range of kinetic energy, and only a small fraction of the particles will have enough energy to actually break bonds so that a chemical reaction can take place. The minimum energy that is needed for a reaction to take place is called the activation energy . For more information on the energy of reactions, refer to Grade 11.

Activation energy

The energy that is needed to break the bonds in reactant molecules so that a chemical reaction can proceed.

Even at a fixed temperature, the energy of the particles varies, meaning that only some of them will have enough energy to be part of the chemical reaction, depending on the activation energy for that reaction. This is shown in [link] . Increasing the reaction temperature has the effect of increasing the number of particles with enough energy to take part in the reaction, and so the reaction rate increases.

#### Questions & Answers

can someone explain the advantages of alternating current?
During a reaction between magnesium sulfate and lead phosphate in a galvanic cell one of the electrode losses 2,4 grams of mass.What is the current that flows in the circuit in 1 second?
During the reaction of Lithium and oxygen where did they get the mass of one moles
Petrina
how to make the rice table in order to calculate Kc
what is a thermsl cracking and what happens in it?
how do you see a product if it is exothermic
When ∆H<0
Thuto
H<0
Dikeledi
does these circles shown show the observer ?
no the circles show the sound detected by the observer
Siphelele
can you mix kc nd pressure
I think KC is only associated with temperature
Siphelele
equation for dissociation
under which topic
Phila
acids and bases
Amanda
Newton's law
Anna
it the bases that dissociate
Amahle
How does a catalyst affect the rate of chemical reaction
it speeds up the reaction without being by the reaction. in other words it increases the Reaction rate by lowering the activation energy of a reaction
Keabetsoe
hey
Siphokazi
ey
Keabetsoe
🙄
Holy
it only speed up the reaction not to affect the reaction
John
and therefore at the end of reaction it is released .. meaning that it hasn't caused any changes
Siphelele
hey
Kedihileng
Phumla
it utters the rates of a chemical reaction
Young
what is a compound?
define Doppler effect
It is the change in frequency of a wave in relation to an observer who is moving relative to the wave source.
Junior
Doppler effect is the change in frequency or pitch detected by a listener because the velocity of the sound source is different from that of a listener relative to the medium of sound propagation
John
explain how color is an unreliable clue to.the identify minerals
Hi I want to know where the topic for electric circuits are?
hello.. How to deal with Reactions rate?. i dont Understand them
Firstly you must know how energy changes during chemical reactions...secondly the collision theory.... Rate and extent of reactions.... And factors that affect the rate of chemical reactions... If u capture all the topic then this chapter will be easy for you the is no way you can fail it...
Pearly
thank you
Petty
Heii.. I'm struggling with chemical equilibrium.
Ronny
how do I attempt chemical equilibrium?
Ronny
also understand the graphs
Siphelele
doppler effect question
How do I differentiate from the formula of a listener who is moving away and who is moving towards the source
Njabulo
if the its away you will subtract on the numerator and add in the denominator but if its towards its the opposite
Ashley