St. John Ogilvie High School
Curriculum for Excellence
Topic 2
Speed of Chemical Reactions
INTERNET NOTES
1
Curriculum for Excellence—Experiences and Outcomes
Science
Chemical changes
Learners gradually develop an understanding of chemical changes. They consider processes
which take place in the environment and in the laboratory, and develop their understanding of
the environmental impact of some changes. They develop their understanding of energy changes
in chemical reactions and some of the factors affecting the rates of reactions. Learners develop
the use of chemical names, formulae and equations as a way of conveying information about
chemical changes.

I have collaborated in activities which safely demonstrate simple chemical reactions using
everyday chemicals. I can show an appreciation of a chemical reaction as being a change in
which different materials are made. SCN 2-19a

Through experimentation, I can identify indicators of chemical reactions having occurred. I
can describe ways of controlling the rate of reactions and can relate my findings to the
world around me. SCN 3-19a
2
Science Experiences and Outcomes—unpacked
Learning Intentions
By the end of this topic I will be able to:
speed of a reaction:

particle size

concentration

temperature
give examples of reactions (both laboratory and everyday) affected by the following:

particle size

concentration

Temperature
state that catalysts are substances which:

speed up some reactions

are not used up during the reaction

can be recovered chemically unchanged
give everyday examples of uses of catalysts, eg transition metals in car exhaust systems.
3
Chemical Reaction in the Laboratory
Different chemical reactions take place at different rates.
Experiment 1
Magnesium + water
Fill the test-tube with water
and insert it in a beaker of
water as shown. (be careful
not to let any air into the test
-tube)
Put a piece of magnesium ribbon (5cm) under the mouth of
the test-tube.
Leave the experiment set up for a few days.
Magnesium reacts with water to produce hydrogen gas so you can get some idea of
the speed of the reaction by seeing how fast the gas is produced.
Barium chloride + sodium sulfate solution
1.
2.
3.
Add about a 2cm depth of sodium sulfate solution to a test tube.
Add a few drops of barium chloride solution from a dropper.
What do you see happening? Is this a fast ,medium or slow reaction?
Zinc + hydrochloric acid
1.
2.
3.
4
Add about 2cm depth of hydrochloric acid to a test tube.
Add a single granule of zinc metal
What do you see happening? Is this a fast ,medium or slow reaction?
Complete the following table:
Reactants
Reaction speed
Magnesium + water
FAST
Barium chloride solution + sodium sulfate solution
VERY FAST (INSTANTLY CHANGED)
Hydrochloric acid + zinc
SLOW
Do all chemical reactions occur at the same speed?
NO
Experiment 2—Particle size and the acid chalk reaction.
In this experiment you are going to complete it as an Investigation. Your teacher
will take you though how to complete an investigation.
You will first look at a PowerPoint to help you with the experiment and then another
presentation to help you with the investigation booklet.
Now that you have completed your investigation write a few sentences to explain
how particle size can affect the speed of a chemical reaction:
By making the particles smaller, the
overall surface area of the reactants
increase. This means more particles can
bounce off of each other and so the
reaction will be fast.
The smaller the particles, the faster the chemical reaction.
Experiment 3—Effect of temperature of a Glucose reaction.
Follow the instructions described below:
1.
2.
3.
4.
5
Pour about 5cm3 of glucose solution in each of 3 test tubes.
Add 1-2cm3 of the blue Benedict’s solution to each.
Put on test tube in a beaker of cold tap water, another in a beaker of hot tap
water and the third in very hot water (90-100oC)
Complete the write-up on the next page.
Aim:
The Aim of this experiment is to investigate the effect of temperature change of
the speed of a chemical reaction.
Apparatus:
Method:
The apparatus as set up as shown above. 3 cm3 of glucose solution was poured
into three test tubes. 2 cm3 of Benedict’s solution was then added into each test
tube. The test tubes were placed into beakers of cold, hot and boiling water as
shown above. A stopwatch was started and the time recorded for how long it
took for the solutions to change colour.
Results:
Temperature of Water
Time for solution to change
colour (s)
Cold
1200
Hot
600
Boiling
120
Conclusion:
The higher the temperature the faster the chemical
reaction.
Increasing the temperature will make the reaction go
faster.
6
Experiment 4—Effect of Concentration
When two chemicals A and B are mixed they react to form tiny particles of sulfur
which make the mixture cloudy.
If we measure how long it takes for the solution to become cloudy, we call tell how
fast the reaction is.
1.
2.
3.
4.
5.
6.
7.
Lightly, draw a cross in pencil on
filter paper
Place a clean 100cm3 beaker on the
cross.
Add the required number of drops
of acid A to the beaker.
Measure out 25cm3 of solution B in
a measuring cylinder.
Pour the 25cm3 of solution B into
the beaker and start the stopwatch.
Stop the stopwatch when you can no longer see the cross through the solution,
and note the time.
Clean the beaker thoroughly and repeat steps 2 to 6 until the table below is
complete.
Number of drops of acid A
Concentration
Time (seconds)
5
Low
600
10
Medium
400
15
High
100
If we increase the concentration of one of the chemicals
in a reaction the speed of the reaction will increase.
The higher the concentration the faster the chemical
reaction
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Rates of Chemical Reactions
From the experiments we have done so far we have found that the reate of a
chemical reaction can be increase by:
1.
2.
3.
Increase the surface area of a solid. (Breaking it up into smaller and smaller
bits)
Increase the temperature .
Increase the concentration of the chemicals reacting.
Everyday reactions:
Describe two everyday reactions in which changing the particles size changes the
rate of reaction.

Small potatoes cook faster than large potatoes

Small lumps of coal will burn faster than large lumps.
Describe two everyday reactions in which changing the temperature changes the
rate of the reaction.

Milk will turn sour more slowly in a refrigerator than left out on the kitchen
table (lower temp.)

Plants will grow faster in warmer conditions than in colder ones.
Describe two everyday reactions in which changing the concentration changes the
rate of reaction.

Blowing air (increasing the concentration of oxygen) into a BBQ will make the
charcoal burn faster.

Two antacid tablets will neutralise more stomach acid that one.
Experiment 5— Using a catalyst
1.
2.
3.
4.
5.
Put about 1cm depth of hydrogen peroxide into a
clean test-tube.
Test for oxygen by putting a glowing splint to the
mouth of the test-tube.
Add a very small amount of black powder called
manganese dioxide to the hydrogen peroxide.
Again test for oxygen (as described in step 2).
Record your result.
(Your teacher may ask you to repeat the experiment using a sliver of potato instead
of manganese dioxide.)
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Aim:
The aim of this experiment is to investigate the effect of using a catalyst on the
speed of a chemical reaction.
Apparatus:
Method:
Hydrogen peroxide was powered into a test. A splint was then lit, blown out, and
placed in the mouth of the test time.
Manganese dioxide (the catalyst) was then added to the hydrogen peroxide. The
splint was then lit, blown out, and placed into the mouth of the test tube.
Results:


With no manganese dioxide. The Glowing split did not do
anything when placed into the mouth of the test tube.
With manganese dioxide. The glowing splint ”re-lit” when placed
into the mouth of test tube.
Conclusion:
Using a Catalyst will increase the speed of a chemical
reaction.
Advantage – faster reactions and the catalyst can be used
again and again.
9
A catalyst is a substance which speeds up a chemical reaction but i not
changed by the chemical reaction. The catalyst can be recovered at the end of
the reaction and used again.
Hydrogen peroxide is a colourless liquid which gives off oxygen gas. This normally
happens so slowly that not enough oxygen is given off to relight a glowing splint.
Hydrogen peroxide
water + oxygen
Why does the chemical industry use catalysts to speed up reactions?
This will allow companies to make more of their desired product (perhaps a chemical or a
drug) faster and make more money. Although catalysts are expensive, they can be used again
and again so will only need to be bought once.
Name of catalyst
Substance manufactured
Nickel
Used to make margarine
Iron
Used to make ammonia in a
process called the Haber Process.
Vanadium (V) oxide
To make sulfuric acid.
Why do manufactures fit catalysts to the car exhaust systems and what is the
catalyst used?
Catalyst in catalytic converters turn harmful gases
into less harmful gases.
10
Biological Catalysts—Enzymes
Living things make use of biological catalysts called enzymes. They are proteins that
allow reactions to take place more quickly at lower temperatures.
In recent years the science of Biotechnology has developed and increased the use of
enzyme catalysts in industrial processes.
Such catalysts include zymase in yeast to make alcoholic drinks, amylase to breakdown starch and protease enzymes in washing powder.
Scientists have found that enzymes work best a certain temperatures i.e. There is
an optimum temperature giving the fastest speed of reaction. In wine making the
yeast works fastest at about 27oC. If the temperature is above or below this the
reaction will take place more slowly.
In our bodies the optimum temperature for enzyme activity is about normal body
temperature of 37oC.
Questions:
1.
What are catalysts in living things called?
2.
Name four products made with the help of this type of catalyst:
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Summary File
Fill in the blanks in the following statements using words from the list below.
Note: there are no extra words, but some words maybe used more than once.
Again
Faster
Low temperature
Speed
Catalyst
High
Particle
Undiluted
Chemical
Higher
Platinum
Used up
Different
Lower
Slowly
1.
Chemical reactions occur at different speeds (or rates).
2.
The smaller the particle size, the faster the reaction.
3.
An acid which has been diluted three times reacts more slowly than the
undiluted acid.
4.
Normally the higher the temperature the faster the reaction.
5.
Enzymes are biological catalysts which allow reactions in living things to occur
at lower temperatures.
6.
Catalysts speed up reactions and are not used up so they can be used again and
again.
7.
Some catalytic converters in car exhausts contain the very expensive metal
platinum.
8.
A fridge keeps food fresh because the Low temperatures slows down the
speed the enzymes react at (i.e. The chemical reactions go more slowly. )
12