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GCSE Questions and Answers
Kinetics and Energetics
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6 consecutive GCSE Chemistry papers: 2002-7
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Particles must collide in order to react.
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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!
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Successful collisions have the correct orientation and sufficient energy.
The collision energy is needed to break bonds in the reactant molecules.
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O=O + 2 H-H 2 H-O-H496 (2 X 436) (4 X 463)Energy Units Energy Units Energy Units
------------------------------------Bonds broken = 1368 Bonds made = 1852-------------------------------------Difference = 484 more energy units released
to surroundings – which warm up
The reaction is therefore EXOTHERMIC
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]
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]
b) The results obtained in one experiment are shown in the table below.
(i) Plot these data on the graph opposite [4]
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
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]
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Low High
Concentration
3 Hydrogen peroxide decomposes very slowly at room temperature to produce oxygen gas and water.
2H2O2 → 2H2O + O2
An increase in temperature and the addition of a catalyst will increase the rate of decomposition.
2004, Paper 1
When conditions are warmer particles have more energy and move around faster.
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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.
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Catalysts are not used up
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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.
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Reaction CatalystDecomposition of hydrogen peroxide
Manganese (iv) oxide, MnO2
Manufacture of ammonia by the Haber Process
iron
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
Catalysts that will learn about in GCSE.
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
5 The diagram below shows part of the label from a packet of antacid tablets.
FizzersAntacid Tablets
IngredientsCitric AcidSodium HydrogencarbonateSodium SaccharinLemon Flavouring
2005, Paper 1
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.
SodiumHydrogencarbonate +
Citric Acid →
SodiumCitrate +
CarbonDioxide
+ Water
(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 Mass (g)
101.33 101.12 101.00 100.93 100.90 100.90
Time(s) 0 20 40 60 80 100
Total Mass (g)
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.
Time(s) 0 20 40 60 80 100
Total Mass (g)
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]
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The more you break it up the greater its surface area.
A greater surface increases the number of collision per unit time.
More frequent successful collisions results in a faster reaction.
Solid
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Flour Dust Explosion Kills over 50!
Releasing the energy of a reaction too quickly can have devastating consequences!
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Marble + Acid = Salt + CO2 + H2OCaCO3 + 2HCl = CaCl2 + CO2 + H2O The same mass of marble was used in each experiment but the surface area varied.
CO2 bubbles frothing over
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(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]
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)
2006, Paper 1
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.
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Na2S2O3(aq) + 2HCl(aq) S(s) + 2NaCl(aq) + H2O(l) + SO2(g)thiosulphate + acid insoluble sulphur causes cloudiness
Race to hide the X
Equation not required!
CARE: SO2 is highly poisonous and may bring on attacks of asthma. USE A FUME CUPBOARD.
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The higher the concentration of the acid the faster the reaction takes place. Required 44s for 1.0 M AcidRequired 60s for 0.5 M Acid
At higher concentrations: Acid particles collide more frequently with thiosulphate particles and the frequency of successful collisions rises.
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 for cross to
disappear (s)
3Rate of reaction (s-1)
1 0.4 105 0.0095
2 0.8 79 0.0127
3 1.2 54 0.0185
4 1.6 32
time
1
(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]
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]
2007, Paper 2
83
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.
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 [1]C beehive shelf [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]
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Recall:We used glucose to reduce/decolourise purple potassium permanganate.
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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 movingparticles that raise the temperature- and not the other way around!
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
Ammonia
Nitrogen Monoxide → Nitrogen Dioxide → Nitric Acid
Equation [3]
Catalyst [1]
Temperature (°C) [1]
Pressure (atm) [1]
Equation [3]
Catalyst [1]
Temperature (°C) [1]
Pressure (atm) [1]
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]
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