1. Unit 1 - Chemical Changes and Structure Section 1 – Rates of Reaction
National 5
Unit 1 - Chemical Changes and Structure
Section 1 – Rates of Reaction

2. We will be learning…
To follow the course of a reaction through change in mass, volume and other quantities that can be measured.
To draw graphs to represent; end-point of a reaction, quantity of product and reactant and the effect of changing conditions.
In terms of Collision Theory be able to describe how the rate of reaction can be increased by increasing the temperature
In terms of Collision Theory be able to describe how the rate of reaction can be increased by increasing the concentration of a reactant
In terms of Collision Theory be able to describe how the rate of reaction can be increased by increasing the surface area/decreasing particle size
In terms of Collision Theory be able to describe how the rate of reaction can be increased by using a catalyst
To calculate average rate of reaction with appropriate units at different stages in the reaction

3. What are the Signs of a Chemical Reaction?
Colour Change
Solid Forming (Precipitate)
Energy Change (heat or light)
Gas Released (see, smell, hear)

4. Speed of Chemical Reactions
Chemical reactions are taking place around us all the time. They happen at a wide range of ________ from millions of __________ to a fraction of a _________ in the case of an explosion.
speeds
years
second
Slow
Fast

5. How can we Measure how fast a Reaction is going?
Rate is the speed at which a chemical reaction proceeds per unit of time.
There are two ways to find the rate of a reaction:
Measure the rate at which a reactant is used up
Measure the rate at which a product is formed.
The method chosen depends on the reaction being studied.

6. Measuring Mass of Reactants Lost
Method
Pour 50cm3 of Hydrochloric acid into a conical flask, put a piece of cotton wool in its mouth and place on a balance.
Using a small beaker, weigh out 10g of marble chips and place it on the balance as well.
Record the initial mass in the following table.
Take out the cotton wool and pour in the marble chips, start the stop watch and replace the cotton wool.
Measure the mass every 30 seconds, calculate the mass lost, and put your results in the table.

7. Results Draw a graph of your results Write a conclusion and evaluation
Time (s)
Mass (g)
Mass Lost (g)
330 30 60
Draw a graph of your results
Write a conclusion and evaluation
Answer the questions in sentences

8. Choose one of the methods for collecting gas.
Measuring the volume of a gas
Choose one of the methods for collecting gas.
Use the same reaction conditions to measure the volume of gas produced.
Measuring the volume of gas using a syringe

9. Results Draw a graph of your results Write a conclusion and evaluation
Time (s)
Mass (g)
Mass Lost (g)
330 30 60
Draw a graph of your results
Write a conclusion and evaluation

10. Particle Size
A lump of coal or wood will burn slowly in air. This means that the chemical reaction is taking place slowly. We can speed up the reaction by using smaller pieces.
For example wood shavings burn faster than logs. If we use a powder then the reaction is even faster. Powdered coal is often used in some power stations.
The speed of burning depends on the size of the particles and how large a surface area can be in contact with the air at one time.
Decreasing the particle size increases the rate of reaction by increasing the surface area.

11. Results: Beaker 1 Beaker 2
Aim: to find out what effect decreasing the particle size has on a reaction with marble chips.
Collect: 1 lumps of marble and a spatula full calcium carbonate of relative size, 2 200ml beakers and 40ml 1 mol l-1 hydrochloric acid.
Results: Beaker 1
Beaker 2
Conclusion: Using smaller particles will ________ the speed of a reaction.
increase

12. Particle Size and Collisions
1M acid 25˚C
1g marble
48 Marble Ions on Surface
28 Marble Ions on Surface
Increased Rate of Collision
Smaller Particles
Faster Rate of Reaction
Greater Surface Area for Collision

13. Concentration
Generally, when we increase the concentration of the reactants we increase the speed of a reaction.
Now try experiment 2, which looks at increasing the concentration of hydrochloric acid.
Copy the diagrams below showing how a concentrated acid and a dilute acid react with a piece of magnesium.

14. Results – complete the table with your results Concentration of Acid
Time to react (Mins/Secs)
Conclusion – Copy and complete the following:
When we add the magnesium to the ______ acid we only see a ______ bubbles forming. However, when we add the magnesium to the ___________________ acid we see ________ of bubbles forming.
dilute
few
concentrated
lots
Increasing the concentration will _____________ the speed of a reaction.
increase

15. Concentration and Collisions
Collision Theory
Substances React only if they Collide with Sufficient Energy to Break Existing Bonds
1g marble lump 25C
Greater Concentration of Acid Ions in 4M HCl
More Collisions/sec with Marble Ions
Faster Rate of Reaction

16. Temperature
When a reaction mixture is heated up the particles in the mixture are given more energy and therefore move around faster. This means that the particles collide more often, which makes the reactions go faster.
Now try experiment 3, which looks at increasing the temperature of the reaction mixture.
Record your results on the following diagram and then complete the results table and conclusion.

17. Increasing the temperature will _____________ the speed of a reaction.
Results – complete the table with your results
Test Tube
Result
Cold Water
Warm Water (40-50٥C)
Hot Water (90-100٥C)
Conclusion – Copy and complete the following:
Increasing the temperature will _____________ the speed of a reaction.
increase

18. Temperature and Collisions
1g marble lump in 1M acid
Particles Move Faster
Collisions More Frequent
Higher Temperature
Faster Rate of Reaction
Much More Important
Particles have More Energy
Collisions More Successful

19. Catalyst Hydrogen peroxide and Manganese dioxide
Chemists use special substances called catalysts to speed up reactions. Catalysts remain unchanged and do not get used up in reactions.
Now try experiment 4, which looks at using a catalyst to speed up a chemical reaction.
Record your results on the following diagram and then make a results table and draw a conclusion.
Adding a catalyst to a reaction _______ _____ the rate of reaction.
Hydrogen peroxide and Manganese dioxide
speeds up

20. Catalyst mechanism and collison theory

21. Catalyst Poisoning
This can occur if impurities are adsorbed on to the surface of the catalyst taking up sites which could otherwise have been occupied by reactant particles.
e.g. lead poisons the platinum catalytic converters used to catalyse the complete combustion of exhaust hydrocarbons and carbon monoxide in car exhaust systems.
In a Catalyst for removing nitrogen oxides, whose activity is lowered by poisoning with sulphur oxides, is contacted with an ammonia gas at a temperature of 200° to 500° C, whereby the sulphur oxides are liberated from the catalyst, and the catalyst is regenerated.
To remove the impurities blocking the active sites on a catalyst is called regeneration.

22. Aluminosilicate Cracker ‘Cat’ Burned free of Soot
Removing ‘Cat’ Poison
Aluminosilicate Cracker ‘Cat’ Burned free of Soot
Regeneration

23. Enzymes Enzymes are biological catalysts
They catalyse the chemical reactions that take place in the living cells of plants and animals
The human body contains over 30,000 different enzymes. The reason for so many is that they are specific so they can catalyse only one reaction.
e.g. Liver contains
the enzyme catalase
which speeds up the
decomposition of
hydrogen peroxide.

24. Catalase and Hydrogen Peroxide
HP COW
Hydrogen peroxide is a harmful chemical found in all cells.
An enzyme called catalase speeds up the breakdown of hydrogen peroxide into oxygen and water.
catalase
Oxygen + Water
Hydrogen Peroxide
Catalase is found in all living cells.

25. Catalase and Hydrogen Peroxide
Method
Add 5cm3 hydrogen peroxide to 4 test tubes.
Add a small piece of potato to test tube A and liver to test tube B
Add the same size of boiled potato to C and boiled liver to D.
4 Leave for two minutes.
5 Measure the height of bubbles in each test tube.
(Bubbles indicate that the reaction has taken place) E
Hydrogen peroxide
Control r

26. A B C D E + + + + + Bubbles of oxygen Hydrogen peroxide Raw Potato
Raw Liver
Hydrogen peroxide +
Boiled Potato
Hydrogen peroxide +
Boiled Liver
Hydrogen peroxide +
boiled liver

27. Collision Theory and the Correct Geometry
The reaction can only happen if the hydrogen end of the H-Cl bond approaches the carbon-carbon double bond with the correct geometry. Any other collision between the two molecules doesn't work. The two simply bounce off each other.

28. Collision Theory Definitions:
The particles (atoms/molecules or ions) must have the correct energy and collide with the correct geometry for successful collisions to occur e.g. for the reactants to react and form the products.
Concentration – The higher the concentration the greater number of particles are present therefore there will be more successful collisions which potentially increases the rate of reaction.
Particle Size – The smaller the particle size the greater surface area there is which exposes more reactant particles therefore resulting in a greater chance of successful collisions which increases the rate of reaction.
Temperature – the higher the temperature then the higher energy level of the reactants. This means that the particles are moving around more increasing the chance of successful collisions and a faster reaction rate.

29. Drawing Graphs

30. Simple Rules to Remember
P Points
L Label
U Units
S Scale
PLUS

31. Rules for Drawing Graphs
1. Use a pencil, ruler and more than half of the graph paper.
2. Read the question carefully to find out if you have to
draw a line graph or a bar chart
3. The things you are plotting are called the variables.
The variable which you control is plotted on the
horizontal axis (along the bottom). The variable that
you measure during the experiment is plotted on the
vertical axis (up the way).

32. e.g. if you were asked to plot a graph of distance (km) traveled against time (Hrs), time is plotted on the horizontal axis and distance on the vertical axis.

33. 6. Give the graph a title – see above
4. Label the axes and give the units of the variables e.g. temperature °C
5. For a line graph join the points with either one straight line or a smooth curve. Do not draw straight lines between pairs of points.
6. Give the graph a title – see above
7. To practice drawing graphs plot the following points on separate graphs:

34. Experiment 1
Temperature °C 14 26 38 50 62 74 86 98
Time (mins) 1 2 3 4 5 6 7 8
Experiment 2
Volume of
gas (cm3) 15 28 38 47 55 62 68 74 78
Concentration
of acid (mol l-1)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9

35. What is wrong with this bar graph?
Bars different widths
No labels for bars
No label for vertical axis
Scale of vertical axis is not regular
Ruler was not used correctly to draw one of the bars 11 10 4
Type of drink

36. What’s Missing from this Graph?

37. Reaction Progress H2O 2HCl + + Carbon dioxide CO2 Calcium chloride
Water
H2O
Hydrochloric Acid
2HCl + +
Carbon dioxide
CO2
Marble
Calcium chloride
CaCl2 +
CaCO3
Volume CO2/cm3 4 8 12 16 20 2 6 10 14
Time/min
Fastest
Slowing
Stopped

38. Calculating Average Rate of Reaction
The rate of reaction at any moment in time is given by the slope of the graph at that time. The slope of the graph decreases with time.
It is easier to measure the average rate of a reaction over a period of time than to measure the rate at a particular moment in time since the latter is always changing.
The average rate of reaction can be given by;
Average Rate of reaction = ________________
The units are quantity per second e.g. gs-1 or cm3s-1
Change in quantity
Change in time

39. Calculating Rate From Progress Graphs
ΔV=04
88-84
ΔV=02
90-88
ΔV=00
ΔV=08
84-76
ΔV=14
76-62
ΔV=22
62-40
ΔV=40
40-0
Progress Graph for the Reaction:
Mg + 2HCl
MgCl2 + H2

40. Average Rate(ΔV/t)/cm3s-1 Time Interval/s 20
Volume Change/cm3
Average Rate(ΔV/t)/cm3s-1
Time Interval/s 20 40 22 14 8 4 2
2.0
1.1
0.7
0.4
0.2
0.1
0.0
Average Rate since as Time
both [Reactants] and Rate
Units – Mass(g.min-1), Volume(cm3.s-1), Conc.(mol.l-1.s-1)
Rate:
is maximum at Start
Average Rate/cm3s-1
is never Constant
decrease Non Linear

41. Comparing Temperature and Reaction Progress10 18
higher temperature
High Temp.
lower temperature
Low Temp.
Zinc + Hydrochloric Acid
22.5
Zinc chloride + Hydrogen
10.0
Conditions
Curve
Volume at 1 min(cm3)
Completion Time(min)
Explanation
Steep
Faster
Shallow
Slower
Same Final Volume
Same Quantities of Reactants

42. Comparing Concentration Reaction Progress
Mass of CO2 Lost
Marble + Hydrochloric acid
199.1
Calcium chloride + Water + Carbon dioxide
lower concentration
Low Conc.
198.4
higher concentration
High Conc.
6.5 14
Mass of Flask, Excess Reactants and Products (except CO2)
Conditions
Curve
Mass at 1 min(g)
Completion Time(min)
Explanation
Steep
Steep
Faster
Faster
Shallow
Slower
Shallow
Slower

43. Comparing Catalysed Reaction Progress
Cu catalysed reaction
Cu Cat 20 12
Uncatalysed reaction
No Cat 62
Zinc + Sulphuric Acid 42
Zinc sulphate + Hydrogen
Conditions
Curve
Volume at 5 min(cm3)
Completion Time(min)
Explanation
Steep
Faster
Shallow
Slower
Same Quantities of Reactants
Same Final Volume

44. Result of a Positive Test
Gas Reactions
You need to be able to carry out and describe the gas tests for oxygen, carbon dioxide and carbon dioxide
Gas
Result of a Positive Test
Oxygen
Hydrogen
Carbon Dioxide
Relights a glowing splint
Burns with a squeaky pop
Turns lime water milky

45. Making a Fire Extinguisher
You need to test different combinations of chemicals that produce the most effective gas – carbon dioxide. You are only allowed to test 1 solid and 1 liquid at a time. Make sure you record your results in the table.

46. Now I can…..
Follow the course of a reaction through change in mass, volume and other quantities that can be measured.
Draw graphs to represent; end-point of a reaction, quantity of product and reactant and the effect of changing conditions.
Describe Collision Theory and how the rate of reaction can be increased by increasing the temperature
Describe Collision Theory and how the rate of reaction can be increased by increasing the concentration of a reactant
Describe Collision Theory and how the rate of reaction can be increased by increasing the surface area/decreasing particle size
Describe Collision Theory and how the rate of reaction can be increased by using a catalyst
To calculate average rate of reaction with appropriate units at different stages in the reaction