Transcript Slide 1

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GCSE Questions
and Answers
Kinetics and
Energetics
6 consecutive GCSE Chemistry papers: 2002-7
1
Particles must collide in order to react.
2
Any factor that increases either the
frequency of collisions or the speed of
collisions will speed up the reaction
Faster moving particles collide:
• more frequently
• harder
More collisions – More effective
collisions - per unit time!
3
Successful collisions have the
correct orientation and sufficient
energy.
The collision energy is needed to
break bonds in the reactant
molecules.
4
O=O
496
Energy Units
+
2 H-H
(2 X 436)
Energy Units

2 H-O-H
(4 X 463)
Energy Units
-----------------------------------Bonds broken = 1368
Bonds made = 1852
------------------------------------Difference = 484 more energy units released
to surroundings – which warm up
The reaction is therefore EXOTHERMIC
5
2002, Paper 2
6a) In an experiment to investigate the
rate of reaction, a piece of
magnesium ribbon was allowed to
react with an excess of dilute
hydrochloric acid at room
temperature. Draw a labelled
diagram of apparatus which is
suitable for carrying out this reaction
and measuring the volume of gas
given off.
[5]
6a) In an experiment to investigate the
rate of reaction, a piece of
magnesium ribbon was allowed to
react with an excess of dilute
hydrochloric acid at room
temperature. Draw a labelled
diagram of apparatus which is
suitable for carrying out this reaction
and measuring the volume of gas
given off.
[5]
b)
The results obtained in one experiment are
shown in the table below.
Volume of gas (cm3) 0 18.5 33.0 43.0 49.5 54.5 57.5 59.0 59.0 59.0
Time (s)
(i)
0 20
40
Plot these data on
the graph opposite
[4]
60
80
100 120 140 160 180
Volume of gas (cm3) 0 18.5 33.0 43.0 49.5 54.5 57.5 59.0 59.0 59.0
Time (s)
0 20
40
60
80
100 120 140 160 180
(ii) At what time was the volume of gas
collected equal to 35cm3?
___________________________ [1]
(iii) During which 30 second time
interval was the reaction fastest?
___________________________ [1]
(ii) At what time was the volume of gas
collected equal to 35cm3?
44 ± 1 [1] seconds
(iii) During which 30 second time
interval was the reaction fastest?
From 0 – 30 [1] seconds
(iv) Explain why the last part of the line
in this graph is horizontal.
___________________________ [1]
(iv) Explain why the last part of the line
in this graph is horizontal.
All the magnesium has been used up
or reaction has stopped [1]
c)
The reaction was repeated using
10cm3 of the same acid mixed with
10cm3 of water. The acid remained
in excess.
(i) Sketch on the graph a line
representing the results you would
expect to find in this experiment.
Label the graph B.
c) (i) See graph; starts
slower from the
origin [1] stays
lower [1] ends up
at same volume
[1]
(ii) Explain, as fully as you can, why
graph B is the shape you have
drawn.
_____________________________
_____________________________
___________________________ [4]
(ii) Explain, as fully as you can, why
graph B is the shape you have
drawn.
Addition of water makes acid less
concentrated [1] as concentration
decreases [1] rate decreases [1]. All
magnesium is used up so final
volume of gas remains at 59cm3 [1]
Concentration
Low
High
19
2004, Paper 1
3
Hydrogen peroxide decomposes very
slowly at room temperature to produce
oxygen gas and water.
2H2O2 → 2H2O + O2
When conditions are warmer
particles have more energy and
move around faster.
An increase in temperature and the
addition of a catalyst will increase the rate
of decomposition.
Catalysts assist chemical reactions.
Gentler collisions are successful in their
presence.
When the reaction is over the catalyst is
still there.
Catalysts can be “poisoned”. This means
that they react irreversibly, usually with
contaminants and are no longer effective
as catalysts.
Most catalysts are transition elements or
compounds of transition elements.
21
Catalysts are not used up
22
Catalysts bring economic benefits to industry.
Catalysts can be very expensive.
Looked after they will lasts for years.
By speeding up industrial reactions they save
time, energy and millions of pounds
A platinum wire
mesh.
23
Catalysts that will learn about in GCSE.
Reaction
Catalyst
Manganese (iv) oxide,
Decomposition of hydrogen peroxide
MnO2
Manufacture of ammonia by the
iron
Haber Process
Conversion of SO2 into SO3 during
the Contact Process to make
sulphuric acid
Vanadium (v) oxide,
V2O5
Hydrogenation of a C=C double bond nickel
24
a)
Draw a labelled diagram of the
apparatus which could be used to
carry out the reaction at 20oC and to
measure the volume of gas produced
from this reaction against time.
Indicate the position of the catalyst
and hydrogen peroxide.
[5]
b) The graph
opposite shows
the production of
oxygen gas from
the decomposition
of hydrogen
peroxide at 40oC
using 50cm3 of
0.2mol/dm3
hydrogen
peroxide solution
in the presence of
0.5g of solid
catalyst.
(i) On the same axes, sketch the graph
which you would expect to obtain if
the experiment was repeated at 20oC,
all other factors being the same.
Label this graph A.
[3]
(ii) On the same axes, sketch the graph
which you would expect to obtain if
the experiment was repeated with
50cm3 of 0.3 mol/dm3 hydrogen
peroxide at 40oC with 0.5g of solid
catalyst. Show the final gas volume
produced. Label this graph B. [3]
(iii) Explain the role of a catalyst.
__________________________________
_______________________________ [2]
(iv) Explain, as fully as possible, how a higher
temperature can cause an increase in the
rate of a chemical reaction.
__________________________________
__________________________________
_______________________________ [4]
(iii) Explain the role of a catalyst.
Catalyst increases rate [1] without being
used up [1]
(iv) Explain, as fully as possible, how a higher
temperature can cause an increase in the
rate of a chemical reaction.
Particles have more energy/move more/move
faster [1] more collisions [1] hence more
successful collisions/more collisions/with enough
energy to break bonds in reactants in given period
of time [1] so increased rate
2005, Paper 1
5
The diagram below shows part of the label
from a packet of antacid tablets.
Fizzers
Antacid Tablets
Ingredients
Citric Acid
Sodium Hydrogencarbonate
Sodium Saccharin
Lemon Flavouring
a)
When added to water the tablet fizzes,
partly due to the reaction between sodium
hydrogencarbonate and citric acid.
(i)
Citric acid forms salts called citrates.
Complete the word equation below.
Sodium
Citric
+
→
Hydrogencarbonate
Acid
a)
When added to water the tablet fizzes,
partly due to the reaction between sodium
hydrogencarbonate and citric acid.
(i)
Citric acid forms salts called citrates.
Complete the word equation below.
Sodium
Citric
Sodium
Carbon + Water
Hydrogencarbonate + Acid → Citrate + Dioxide
(ii) Use the equation in (a)(i) to explain what
causes the fizz.
_______________________________ [1]
(iii) What is the purpose of an antacid?
_______________________________ [1]
(ii) Use the equation in (a)(i) to explain what
causes the fizz.
Carbon dioxide
[1]
(iii) What is the purpose of an antacid?
To reduce the amount of acid in the
stomach
[1]
(iv) Apart from sodium hydrogencarbonate,
name another compound which is an
antacid.
_______________________________ [1]
(iv) Apart from sodium hydrogencarbonate,
name another compound which is an
antacid.
Aluminium hydroxide/CaCO3/Mg(OH)2 [1]
b)
In an experiment one Fizzers tablet was
added to 50cm3 of water (an excess) in a
conical flask at a temperature of 20°C.
The flask was loosely stoppered with a
cotton wool plug and placed on a balance
and a stopwatch started. The mass was
recorded every 20 seconds.
(i)
Complete the diagram of the apparatus
used for this experiment. Label the
diagram.
(i)
Complete the diagram of the apparatus
used for this experiment. Label the
diagram.
Conical flask on balance [1]
Cotton wool plug [1]
Water with tablet [1]
Stopwatch [1]
Max [3]
(ii) Explain why the total mass of the flask and
its contents decreases during the
experiment.
_______________________________ [2]
(iii) What is the purpose of the cotton wool
plug?
_______________________________ [1]
(ii) Explain why the total mass of the flask and
its contents decreases during the
experiment.
Gas [1] is lost [1]
[2]
(iii) What is the purpose of the cotton wool
plug?
Prevent loss of liquid spray
[1]
c)
The table below shows the results for the
experiment.
Time(s)
0
20
40
60
80
100
Total
101.33 101.12 101.00 100.93 100.90 100.90
Mass (g)
Total Mass (g)
101.4
101.35
101.3
Time(s)
0
20
40
60
80
100
Total
Mass (g)
101.33
101.12
101.00
100.93
100.90
100.90
101.25
101.2
101.15
101.1
101.05
101
100.95
100.9
100.85
0
20
40
60
80
100
120
(i)
Plot these results on the graph provided
and use it to answer the following
questions.
Time(s)
Total Mass
(g)
0
20
40
60
80
100
101.33
101.12
101.00
100.93
100.90
100.90
i) Plot these results on the graph provided and use it to answer the following questions.
(ii)
At what time does the reaction stop?
___________________________________ [1]
(iii) What loss in mass would be expected if half a
tablet is used in 50cm3 of water at 20°C?
Show clearly how you obtained your answer.
___________________________________
___________________________________ [2]
(ii)
At what time does the reaction stop?
78 seconds ±2
[1]
(iii) What loss in mass would be expected if half a
tablet is used in 50cm3 of water at 20°C?
Show clearly how you obtained your answer.
101.33 – 100.90 = 0.43g [1] divided by 2 =
0.215g [1]
[2]
(iv) If the experiment was repeated using one
crushed tablet in 50cm3 of water at 20°C,
state and explain in terms of particles, the
effect this would have on the rate of the
reaction.
Effect __________________________
Explanation _____________________
______________________________
______________________________
______________________________ [1]
(iv) If the experiment was repeated using one
crushed tablet in 50cm3 of water at 20°C,
state and explain in terms of particles, the
effect this would have on the rate of the
reaction.
Effect Speeds up the reaction
Explanation Greater surface area [1] over
which particles can collide more collisions
[1] in unit time/per min/per sec [1] (Max
[2])
[3]
The more you break it up
the greater its surface
area.
A greater surface
increases the number of
collision per unit time.
Solid
More frequent
successful collisions
results in a faster
reaction.
51
Flour Dust Explosion Kills over 50!
Releasing the energy of a reaction
too quickly can have devastating
consequences!
52
Marble + Acid = Salt + CO2
CaCO3 + 2HCl = CaCl2 + CO2
+ H2O
+ H2O
The same mass of marble was used in each
experiment but the surface area varied.
CO2 bubbles
frothing over
53
54
(v) The experiment was repeated using the
same volume of water and one whole
tablet at 40°C. On the same axes, sketch
the graph for this experiment and label it
B.
(v) The experiment was repeated using the
same volume of water and one whole
tablet at 40°C. On the same axes, sketch
the graph for this experiment and label it
B.
Starts at 101.33 [1] stays lower [1] levels
off earlier [1] at same level i.e. 100.9 [1]
2006, Paper 1
2
Sodium thiosulphate solution Na2S2O3(aq),
reacts with dilute hydrochloric acid
according to the following equation:
Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + S(s) + SO2(g) + H2O(l)
The diagram below shows the apparatus
used to investigate the effect of changing
the concentration of sodium thiosulphate
solution on the rate of this reaction.
Race to hide the X
Na2S2O3(aq) + 2HCl(aq)  S(s) + 2NaCl(aq) + H2O(l) + SO2(g)
thiosulphate + acid
insoluble
Equation not required!
sulphur
CARE: SO2 is highly poisonous and
causes cloudiness
may bring on attacks of asthma.
USE A FUME CUPBOARD. 59
At higher concentrations:
Acid particles collide more
frequently with thiosulphate
particles and the frequency
of successful collisions
rises.
The higher the concentration of the acid the
faster the reaction takes place.
Required 44s for 1.0 M Acid
Required 60s for 0.5 M Acid
60
A precipitate is produced which causes the
solution to become cloudy. The rate of this
reaction can be investigated by timing how long
it takes for the cross drawn on the white paper
to disappear from view.
(a) Which product causes the solution to
become cloudy?
_______________________________ [1]
A precipitate is produced which causes the
solution to become cloudy. The rate of this
reaction can be investigated by timing how long
it takes for the cross drawn on the white paper
to disappear from view.
(a) Which product causes the solution to
become cloudy?
Sulphur
[1]
b)
A series of experiments carried out to
investigate the effect of concentration of
sodium thiosulphate solution on the rate of
reaction produced the following results:
Experiment
Concentration of
sodium thiosulphate
solution (mol/dm3)
Time taken
3Rate of
for cross to reaction (s-1)
disappear
 1 
(s)


 time 
1
2
3
4
0.4
0.8
1.2
1.6
105
79
54
32
0.0095
0.0127
0.0185
(i)
State two precautions which should be
taken to ensure a fair test.
_______________________________
_______________________________ [2]
(ii) Calculate the rate of reaction for
experiment 4 and insert the value into the
results table.
(i)
State two precautions which should be taken to
ensure a fair test.
Same conical flask [1], same concentration of
hydrochloric acid [1], same volume of
hydrochloric acid [1], same volume of sodium
thiosulphate / same total volume [1], same
temperature [1], same cross [1]. Do not accept
same AMOUNT. Any two
[2]
(ii)
Calculate the rate of reaction for experiment 4
and insert the value into the results table.
0.03125 (0.0313 or 0.0312)
[1]
(iii) From the results table of the experiments,
state the effect of increasing the
concentration of sodium thiosulphate
solution on the rate of the reaction.
_______________________________
_______________________________ [1]
(iii) From the results table of the experiments,
state the effect of increasing the
concentration of sodium thiosulphate
solution on the rate of the reaction.
Increases
[1]
(iv) Explain, as fully as possible in terms of
particles, how an increase in concentration
of sodium thiosulphate solution has this
effect on the rate of reaction.
_______________________________
_______________________________
_______________________________
_______________________________ [4]
(iv) Explain, as fully as possible in terms of
particles, how an increase in concentration
of sodium thiosulphate solution has this
effect on the rate of reaction.
Number of particles increases [1] more
collisions [1] more successful collisions
[1] idea of frequency / per unit time [1]
(v) Name two other factors apart from
concentration of sodium thiosulphate that
will affect the rate of this reaction.
_______________________________
_______________________________ [2]
(v) Name two other factors apart from
concentration of sodium thiosulphate that
will affect the rate of this reaction.
Temperature [1] volume of HCl [1]
volume of Na2S2O3 [1] concentration of
hydrochloric acid [1]. Any two
[2]
c)
The Haber Process is used to produce
ammonia in industry.
(i)
Write a balanced symbol equation for this
reaction.
_______________________________ [3]
c)
The Haber Process is used to produce
ammonia in industry.
(i)
Write a balanced symbol equation for this
reaction.
N2 + 3H2 → 2NH3
[3]
[1]
[1] + [1] for balancing
The amount of ammonia gas produced (%
yield) from this reaction is affected by both the
temperature and the pressure at which the
process is carried out. The graph below shows
how the amount of ammonia produced from the
reaction changes with both temperature and
pressure.
Increasing pressure pushes the reacting gas particles closer together
and therefore has the same affect as increasing the concentration.
Use the graph below to answer the following
questions.
(ii) What happens to the percentage yield of
ammonia if the pressure is increased at
constant temperature?
_______________________________ [1]
(iii) State the temperature and pressure at
which the greatest yield of ammonia gas is
produced.
Temperature _________________°C [1]
Pressure ____________________ atm [1]
(ii) What happens to the percentage yield of
ammonia if the pressure is increased at
constant temperature?
Increases
[1]
(iii) State the temperature and pressure at
which the greatest yield of ammonia gas is
produced.
Temperature 350°C [1]
Pressure 400 atm [1]
(iv) The conditions usually used in the
production of ammonia are a temperature
of 450°C and a pressure of 200
atmospheres. What is the percentage yield
of ammonia using these conditions?
_______________________________ [1]
(iv) The conditions usually used in the
production of ammonia are a temperature
of 450°C and a pressure of 200
atmospheres. What is the percentage yield
of ammonia using these conditions?
26.2% Accept 26.0-26.5
[1]
(v) Suggest two reasons why industry
compromises by using these conditions
when it is possible to obtain a higher yield
of ammonia using a lower temperature and
a higher pressure.
_______________________________
_______________________________
_______________________________
_______________________________ [2]
(v) Suggest two reasons why industry
compromises by using these conditions
when it is possible to obtain a higher yield
of ammonia using a lower temperature and
a higher pressure.
Implication of dangerous (may cause
explosion with high pressures) [1] / Rate:
too slow at lower temperatures [1] / Cost
of conditions / Profit / Economics [1].
Any two
[2]
2007, Paper 2
2
Different factors affect the speed of a chemical
reaction. Light and the presence of a catalyst are
two of these factors.
a)
Photographic film is a gel containing silver(I)
ions. When light reaches the photographic film,
the silver(I) ions are converted to silver and the
silver appears as dark spots.
Write an ionic equation of the conversion of
silver(I) ions to silver.
___________________________________ [2]
Light can play different roles. Above, it sensitizes one of
the reactants, making it react much faster with the other
reactant. This is the case in photography, where the
exposed parts of the film react faster in the developer
and appear different on the negative and photograph as a
result
Another
example in
organic
chemistry
that you’ll
learn about
in GCE.
83
2
Different factors affect the speed of a chemical
reaction. Light and the presence of a catalyst are
two of these factors.
a)
Photographic film is a gel containing silver(I)
ions. When light reaches the photographic film,
the silver(I) ions are converted to silver and the
silver appears as dark spots.
Write an ionic equation of the conversion of
silver(I) ions to silver.
Ag+ + e- → Ag
[2]
b)
A solution of hydrogen peroxide may be
decomposed using a catalyst. The diagram below
shows an assembled apparatus used to carry out
the decomposition and measure the volume of
oxygen gas produced.
(i)
What labels should be in positions A, B
and C?
A _____________________________ [1]
B _____________________________ [1]
C _____________________________ [1]
(i)
What labels should be in positions A, B
and C?
A thistle funnel
[1]
B conical flask
C beehive shelf
[1]
[1]
(ii) What is the name of the catalyst used in
the decomposition of hydrogen peroxide?
_______________________________ [1]
(iii) What other piece of apparatus could be
used to measure the volume of oxygen
produced?
_______________________________ [1]
(ii) What is the name of the catalyst used in
the decomposition of hydrogen peroxide?
Manganese dioxide / manganese(IV) oxide [1]
(iii) What other piece of apparatus could be
used to measure the volume of oxygen
produced?
Gas syringe
[1]
(iv) What is meant by the term catalyst?
_______________________________
_______________________________ [3]
(v) Write a balanced symbol equation for the
decomposition of hydrogen peroxide.
_______________________________ [3]
(iv) What is meant by the term catalyst?
substance which speeds up/increases the
rate of [1] a (chemical) reaction [1]
without being used up /(chemically)
unchanged at end [1]
[3]
(v) Write a balanced symbol equation for the
decomposition of hydrogen peroxide.
2H2O2→ 2H2O + O2
[3]
[1]
[1]
+[1] for balancing
c)
The volume of oxygen produced bydecomposing
25.0cm3 of a 0.1mol/dm3 solution of hydrogen
peroxide at 10°C, 25°C and 40°C is measured and
plotted on the graph below.
State and explain fully, in terms of particles, the
effect of temperature on the rate of the catalytic
decomposition in hydrogen peroxide.
Effect of temperature ____________________
Explanation: ___________________________
______________________________________
___________________________________ [4]
Recall:
We used glucose to
reduce/decolourise
purple potassium
permanganate.
94
As temperature rises particles do not get
warmer. They move about faster.
They collide harder and more frequently.
The frequency of successful collisions
rises and the reaction goes faster.
Strictly speaking, it is faster moving
particles that raise the temperature
- and not the other way around!
95
State and explain fully, in terms of particles, the
effect of temperature on the rate of the catalytic
decomposition in hydrogen peroxide.
Effect of temperature: increasing temperature,
increases rate / decreasing temperature,
decreases rate [1] (essential)
Explanation: particles have more energy [1]
(essential), more collisions [1] more successful
collision [1] in a given period of time / idea of
frequency [1]. Any two. Maximum [4]
(based on increased temperature)
d)
The manufacture of nitric acid is
represented in the diagram below.
Nitrogen and hydrogen are used to make
ammonia in the Haber Process and the
ammonia is then oxidised using a catalyst.
Complete the two tables giving the equation for each
reaction, the name of the catalyst and the temperature
and pressure used.
Nitrogen & Hydrogen
Equation
[3]
Catalyst
[1]
Temperature (°C)
[1]
Pressure (atm)
[1]
Ammonia
Equation
[3]
Catalyst
[1]
Temperature (°C)
[1]
Pressure (atm)
[1]
Nitrogen Monoxide → Nitrogen Dioxide → Nitric Acid
Equation
N2 + 3H2 → 2NH3
[3]
Catalyst
Iron
[1]
Temperature (°C)
Accept values in range 250 - 500
[1]
Pressure (atm)
Accept values in range 200 - 1000
[1]
Equation
4NH3 + 5O2 → 4NO + 6H2O
[3]
Catalyst
Platinum / (rhodium)
[1]
Temperature (°C)
Accept values in range 700 – 1000
[1]
Pressure (atm)
Accept values in range 1 - 10
[1]
Thanks for viewing.
Do consider using others in this Series of Ten.
100