Transcript Rates of Reaction - Learning on the Loop

Rates of Reaction
•In this unit you will investigate
what makes chemical reactions go
faster. At the end of the unit you
will have a 2 hour practical test.
•This test assesses the
Achievement Standard Science
1.1 “Carry out a practical
investigation” (4 credits).
Chemical Reactions
Chemical reactions occur when the reactant
particles collide with the right orientation
and sufficient energy.
How fast a reaction occurs (the rate of a
reaction) depends on the number of successful
collisions per second.
Four factors affect the rate of a reaction::
Temperature
• Reaction :
• Marble chips with acid
Effect of Temperature on rate of
reaction:
Hydrochloric acid and marble chips
collected (cm 3)
Volume of CO 2
10
High Temperature
8
Normal
6
Lower Temperature
4
2
0
0
5
10
15
Time (min)
20
25
Temperature
– The higher the temperature the faster reactant
particles move i.e. they have more energy.
Therefore there are more collisions and with
greater energy.
Low
Temperature
HClMarbl
e
HClMarbl
e
HClMarbl
e
Bang!
Marbl collision?
Is it an effective
e
HCl
HClMarbl
e
Maybe?
Middle
Temperature
HClMarbl
e
HClMarbl
e
HClMarbl
e
Bang!
Marbl collision?
Is it an effective
e
HCl
HClMarbl
e
Probably!
High
Temperature
HClMarbl
e
HClMarbl
e
HClMarbl
e
Bang!
Marbl collision?
Is it an effective
e
HCl
HClMarbl
e
Definitely !
Effect of Temperature
• Increase in Frequency of collisions
AND
• Increase in energy of collisions
Effect of Surface Area on rate of
reaction:
Hydrochloric acid and marble chips
collected (cm 3)
Volume of CO 2
10
Marble Powder
8
Marble
Chips
6
4
Large Marble
Chunks
2
0
0
5
10
15
Time (min)
20
25
Surface Area
– The greater the surface area of the reactants
the greater the possible number of collisions
between reactant particles.
– The surface area of solid reactants can be
increased by breaking into smaller pieces.
– Reactant chemicals are often dissolved in
solution. This makes the particles more
mobile and so more likely to collide and
therefore react.
Large Chunks
Of Marble
Marbl
e
HCl
Marbl
e
Marbl
e
Marbl
e
Marbl
e
Marbl
e
Marbl
e
Marbl
e
Marbl
e
HCl
Bang!
Marbl
e
HCl
Marbl
e
HCl
Is it or is it not an effective
collision?
Marbl
e
HCl
Only on the outside
Marble Chips
Marbl
e
HCl
Marbl
e
HCl
Marbl
e
Marbl
e
HCl
HCl
Marbl
e
Marbl
e
Bang!
HCl
Marbl
e
Marbl
e
Is it or is it not an effective
collision?
Marbl
e
Marbl
e
Marbl
e
Marbl
e
Around the outside of
each chip
Marble Powder
Marbl
e
HCl
Marbl
e
Marbl
e
HCl
Bang!
HCl
HCl
Marbl
Is it or is it not an effective
e
collision?
Marbl
e
Marbl
e
Marbl
e
Marbl
e
Marbl
e
HCl
Marbl
e
Marbl
e
Marbl
e
Very fast with every tiny
particle
Effect of Surface Area
• Increase in Frequency of collisions
NO Increase in energy of collisions
Effect of Concentration on rate of
reaction:
Hydrochloric acid and marble chips
collected (cm 3)
Volume of CO 2
10
Strong Acid
8
Bench
Acid
6
4
Dilute Acid
2
0
0
5
10
15
Time (min)
20
25
Concentration
– In a solution that has high concentration there
are many reactant particles per mL of
solution. Therefore there are more chances
for reactant particles to collide. Increasing the
concentration increases the rate of reaction.
– The concentration of laboratory solutions is
measured in moles per Litre (mol L-1).
Concentrated Acid
HCl
HCl
HCl
HCl
HCl Marbl
Marbl
e
e
HCl
Marbl
e
HCl
Marbl
HCl
HCl
e
Bang!
Marbl
e
Marbl
Marbl
Marbl
e
e
e
Is it or is it not an effective
collision?
Marbl
e
Marbl
e
Marbl
e
Marbl
e
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
Yes from all angles
Normal “bench” Acid
HCl
HCl
HCl
HCl Marbl
e
Marbl
e
Marbl
e
Marbl
e
Bang!
Marbl
e
Marbl
Marbl
Marbl
e
e
e
Is it or is it not an effective
collision?
Marbl
e
Marbl
e
Marbl
e
Marbl
e
HCl
HCl
HCl
HCl
HCl
Yes from most angles
Dilute Acid
Marbl
e
Marbl
e
Marbl
e
Marbl
Marbl
Marbl
e
e
e
Is it or is it not an effective
collision?
Marbl
e
Marbl
e
HCl
Marbl
e
Marbl
e
Bang!
Marbl
e
Marbl
e
Only occasionally, so very slow
Catalyst
• Reaction :
• Hydrogen Peroxide and
the catalyst
Potassium dichromate
10
Catalyst
8
(cm3)
Volume of O 2 collected
Effect of Catalyst on rate of reaction:
Decomposition of Hydrogen Peroxide
6
No Catalyst
4
2
0
0
5
10
15
Time (min)
20
25
Catalysts
– A catalyst is a substance that speeds up a
chemical reaction without being used up by it.
Catalysts speed up reactions by lowering the
energy necessary for the reaction to occur.
They do this by increasing the proportion of
successful collisions through aligning the
reactants so they are the correct orientation
for the reaction to occur.
Effect of Catalyst
No Catalyst
Energy
Reactants
Catalyst
Products
Reaction Progress
Effect of Catalyst
• Decrease in
activation energy
NO effect on frequency of collisions
1.
2.
3.
4.
Purpose of investigation:
To investigate how temperature affects the rate of
a reaction.
Name the key variables in the investigation:
Temperature; concentration; surface area;
quantity of reactants.
Which variable will be changed? Give a suitable range
of values for this variable.
Temperature: 30oC, 50oC, 70oC. Reactants in
water bath monitored with a thermometer.
What will have to be measured or observed in order to
get some data or information from the investigation?
Time taken for solution to go completely
colourless.
How will it be measured or observed?
Clock or stopwatch.
5.
•
•
•
6.
What other variables are important in the investigation
and will have to be controlled to make it a fair test?
Concentration - all solutions will be of known
concentrations. The same ‘batch’ will be used
throughout the experiment.
Surface area-all reactants are in solution.
Reactant’s volumes will be measured with
measuring cylinders or graduated droppers.
Amount of reactant -Volumes will be measured
with measuring cylinders.
How will you ensure that your results are reliable?
Repeat experiment or confer with other class
members. Take an average.
The Effect of Surface Area On
Reaction Rate
Experimental Reaction
CaCO3 + 2HCl
CaCl2 + CO2 + H2O
Marble is a naturally occurring mineral and is composed
mostly of calcium carbonate. It reacts with acids to form
carbon dioxide and water. The rate of this reaction can
be measured by timing how long it takes for a certain
volume of gas to be produced.
1.
Purpose of investigation:
To investigate the effect of surface area on
reaction rate
2. Name the key variables in the investigation:
Temperature; concentration; surface area;
quantity of reactants.
3. Which variable will be changed? Give a suitable range
of values for this variable.
Surface area. Measure 2g quantities of coarse,
medium and fine calcium carbonate.
4. What will have to be measured or observed in order to
get some data or information from the investigation?
Time taken for 20mL of carbon dioxide gas to be
collected.
How will it be measured or observed?
Use downward displacement of gas (see diagram
later)
5.
•
•
•
6.
What other variables are important in the investigation
and will have to be controlled to make it a fair test?
Temperature – all carried out at room temp.
Concentration – acid will be 1molL-1 for each
surface area.
Amount of reactant -2g quantities of calcium
carbonate measured with a balance. 5mL of
hydrochloric acid measured with a measuring
cylinder.
How will you ensure that your results are reliable?
Repeat experiment and take average
8.
•
•
•
•
•
•
Use the information from the previous sections to help
you write a method for this experiment.
Measure 2g of coarse ground calcium carbonate
and put into a test tube.
Add 5mL of 1 molL-1 hydrochloric acid to a test
tube.
Collect gas as shown in diagram below.
Time how long it takes for 20mL of carbon
dioxide gas to be produced.
Repeat steps 1-4 for medium and fine ground
calcium carbonate.
Repeat experiment three times to ensure
reliability of results.
•
•
•
•
Present your results and observations in a table.
Draw a bar graph of your results.
Describe the trend shown by your graph.
Write a conclusion giving your interpretation of
the results linked to the purpose of the
investigation.
• Explain why surface area affects the rate of the
reaction.
• Evaluate the experiment. This may include:
– changes made to method while collecting data,
– difficulties or possible sources of error in doing the
experiment which effect the reliability of the data
collected and validity of the conclusion,
– any improvements you would make to the method.
Magnesium and Acid – Surface
Area Again.
Magnesium
+ hydrochloric acid
Mg + 2HCl
Magnesium chloride +
hydrogen gas
MgCl2 + H2
1.
2.
3.
4.
Purpose of investigation:
To investigate the effect of surface area on
reaction rate
Name the key variables in the investigation:
Temperature; concentration; surface area;
quantity of reactants.
Which variable will be changed? Give a suitable range
of values for this variable.
Surface area. Measure two 1cm quantities of
magnesium. Leave one whole; cut the other into
small pieces.
What will have to be measured or observed in order to
get some data or information from the investigation?
Time taken for Mg to dissolve
How will it be measured or observed?
Stopwatch
5.
•
•
•
6.
What other variables are important in the investigation
and will have to be controlled to make it a fair test?
Temperature – all carried out at room temp.
Concentration – acid will be 1molL-1 for each
surface area.
Amount of reactant -2g quantities of calcium
carbonate measured with a balance. 5mL of
hydrochloric acid measured with a measuring
cylinder.
How will you ensure that your results are reliable?
Repeat experiment and take average