Rates of Reaction
2003

Question 7.

(a) Define rate of a chemical reaction.
(5)
Calcium carbonate (marble chips) reacts w...
2004
(a)

(b)

(c)
(d)

2005

Question 8.
DEFINE: change in concentration per unit time
[Do not accept ‘mass’, ‘volume’, ‘...
(d)

(e)
(f)

2006

(i)
(ii
)

REASON: greater surface area available (3)
GRAPH: labelled and scaled axes [Accept “time” o...
2007

Question 9

(a) Define the rate of a chemical reaction.
Why does the rate of chemical reactions generally decrease w...
Plot a graph of the volume of gas produced versus time. Explain why the graph is steepest at the beginning. (15)
(e) Use y...
2009
(a)

Question 9
(i)
(ii)
(i)
(ii)
(iii
)

(b)

EXPLAIN: minimum energy required for colliding particles (molecules) t...
2009
(a)

Question 9
(i)
(ii)
(i)
(ii)
(iii
)

(b)

EXPLAIN: minimum energy required for colliding particles (molecules) t...
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  1. 1. Rates of Reaction 2003 Question 7. (a) Define rate of a chemical reaction. (5) Calcium carbonate (marble chips) reacts with hydrochloric acid according to the following equation. CaCO3 + 2HCl = CaCl2 + CO2 + H2O Using simple experiments involving marble chips, CaCO3, and hydrochloric acid, HCl, describe how you could demonstrate the effects of (i) particle size, (ii) concentration on the rate of a chemical reaction. (18) (b) What is a catalyst? (6) Catalytic converters are used in cars. (i) Identify one reaction which is catalysed in the catalytic converter in a car. State one of the environmental benefits of this process. (12) (ii) Name one element used as a catalyst in a catalytic converter. What type of catalysis is involved in a catalytic converter? (9) 2003 Question 7 (a) (i) (ii ) (b) (i) (ii ) 2004 Define: change in concentration per unit time Accept ‘rate of change of concentration’ Do not accept ‘mass’, ‘volume’, ‘quantity’, ‘amount’ in place of ‘concentration’. mass of small particles (powder), equal mass of larger particles (granules, lumps) // (3) added to equal volumes of HCl of same concentration // (3) note times to complete OR observe vigour of reactions OR smaller particles faster (3) equal amounts of equal-sized particles (e.g. powder*) of CaCO3 (3) added to equal volumes of HCl of different concentrations (3) note times to complete OR observe vigour of reactions OR higher conc. faster (3) * “Equal-sized” needed for all particles except powder. (Can be got from clear graph) Catalyst: substance that alters (speeds up) rate of reaction (3) not used up OR chemically unchanged at the end (3) reactant(s) (3) product(s) (3) environmental benefit* (6) allow ‘prevents air pollution’ in all four cases for (3) marks. carbon monoxide (3) to carbon dioxide (3) benefit - CO toxic (6) hydrocarbons (3) carbon dioxide & water (3) prevents smog OR reduces greenhouse effect 6) CO and NO (3) CO2 and nitrogen (3) CO toxic / NO leads to acid rain (6) nitrogen oxides (3) nitrogen and oxygen (3) NOx (or specified NOx)causes acid rain (6) Note: reactant and product marks can be got from equations which need not be balanced. Name: platinum / palladium / rhodium Accept symbols. Do not accept ‘gold’. ANY ONE: (3) Type: heterogeneous OR adsorption (6) (5) (9) (9) (6) (12) (9) Question 8. (a) Define the rate of a chemical reaction. (5) Explain why increasing the temperature has a significant effect on the rate of a reaction. (6) (b) The diagram shows a reaction profile diagram for an endothermic reaction. Name the quantities of energy marked A and B. Copy this diagram into your answer book and indicate clearly on your diagram the likely effect of adding a catalyst on the energy profile for the reaction. (12) (c) Catalytic converters are fitted to all modern cars with petrol engines. Name two elements used as catalysts in a catalytic converter. Name one substance which poisons the catalysts in a catalytic converter. (9) (d) The oxidation of potassium sodium tartrate by hydrogen peroxide catalysed by cobalt (II) ions provides evidence for the intermediate formation theory of catalysis. State the observations you would make when carrying out this experiment. Explain how these observations provide evidence for the intermediate formation theory. (18)
  2. 2. 2004 (a) (b) (c) (d) 2005 Question 8. DEFINE: change in concentration per unit time [Do not accept ‘mass’, ‘volume’, ‘quantity’, ‘amount’ in place of concentration] EXPLAIN: More (greater number of) collisions reach (exceed) activation energy OR more collisions have enough energy for reaction OR more effective collisions (6) [Allow (3) for ‘greater number of high energy collisions’, ’increases energy (velocity, speed) of particles (molecules, reagents, collisions)’ or ‘more collisions’ have the activation energy’] NAME: A: Activation energy [Accept Ea or Eact] (3) B: Heat of reaction / Heat change / ΔH / Heat absorbed / Enthalpy change (3) [Accept ‘energy’ for ‘heat’] COPY: Reduction in activation energy shown (3) Products line shown above reactants line / same ΔH with and without catalyst (3) (5) ELEMENTS: platinum / palladium / rhodium [Allow symbols] ANY TWO: (2 x 3) POISON: lead [lead compounds e.g. tetraethyllead] [Allow symbols] (3) OBSERVE: pink at start of reaction [Accept red] (3) // then bubbling as (3) // reaction mixture turns green (3) // reaction finishes and mixture turns pink again (3) (9) (6) (6) (6) (12) Question 3. Hydrogen peroxide decomposes rapidly in the presence of a manganese (IV) oxide (MnO2) catalyst. (a) Write a balanced equation for the decomposition of hydrogen peroxide. (5) (b) Draw a labelled diagram of an apparatus a student could assemble to measure the rate of decomposition of hydrogen peroxide in the presence of a manganese (IV) oxide (MnO2) catalyst. Indicate clearly how the reaction could be started at a time known exactly, and how the gas produced is collected and its volume measured. (12) (c) A student has a choice of using the same mass of finely powdered manganese (IV) oxide or coarsely powdered (granulated) manganese(IV) oxide. Which of these would you expect to have a greater average rate of reaction over the first minute of the reaction? Give a reason for your answer. (6) A set of results obtained in an experiment to measure the rate of decomposition of hydrogen peroxide, in a solution of known volume and concentration, is given in the table. (d) Plot a graph to illustrate the volume of oxygen produced versus time. (12) (e) Use the graph to determine (i) the volume of oxygen produced during the first 2.5 minutes and (ii) the instantaneous rate of the reaction at 2.5 minutes. (9) (f) What changes would you expect in the graph if the experiment were repeated using a solution of the same volume but exactly half the concentration of the original hydrogen peroxide solution? (6) 2005 (a) (b) (c) Question 3 EQUATION: 2H2O2 → O2 + 2H2O / H2O2 → ½O2 + H2O [Formula 3 balancing 3] DRAW: reaction vessel with hydrogen peroxide and catalyst (3) method of ensuring correct start time e.g. catalyst in neck of horizontal flask; bring flask to vertical and start clock / (3) [N.B. Descriptions of starting reaction and clock at same time must be clear. Adding peroxide from funnel is not acceptable as start time is not exact and volume collected is incorrect due to displacement of air.] / delivery tube connected to gas collection system (syringe or over water) (3) clear method of measuring (e.g. syringe with calibrations or inverted graduated cylinder) (3) [At least one label required] WHICH: finely (3) (5) (12) (6)
  3. 3. (d) (e) (f) 2006 (i) (ii ) REASON: greater surface area available (3) GRAPH: labelled and scaled axes [Accept “time” or “minutes”; “volume” or “cm3”.] (3) points plotted correctly (6) [Allow 3 marks if six or more points plotted correctly; assume (0, 0) is plotted correctly] curve drawn [has to be drawn to (0, 0)] (3) Note: the (6) for points plotted correctly not given if graph paper not used. 26.5 – 28.5 cm3 (3) USE : 6.0 – 8.0 cm3 min-1 [Accept in cm3 s-1] (6) [For answers outside range, (3) may be given for a good tangent drawn at the correct point] WHAT: rise less steep / levels off later (3) maximum volume 20 cm3 / half the final volume / less oxygen produced (3) Note: changes may be shown on the candidate’s graph paper or through a suitable sketch (12) (3) (6) (6) Question 7 (a) Define the activation energy of a chemical reaction. (5) (b) Give two reasons why the rate of a chemical reaction increases as the temperature rises. Which of these is the more significant? Why? (12) (c) Describe how you could investigate the effect of temperature on the rate of the reaction between a 0.1 M sodium thiosulfate solution and a 2 M hydrochloric acid solution. (12) The reaction is described by the following balanced equation. Na2S2O3 + 2HCl → 2NaCl + SO2 + S + H2O (d) When silver nitrate and sodium chloride solutions are mixed a precipitate appears immediately. Explain the speed of this reaction compared to the slower reaction when solutions of sodium thiosulfate and hydrochloric acid are mixed. (6) (e) What type of catalysis occurs in the catalytic converter of a modern car? Give the names or formulas of two substances entering a car’s catalytic converter and the names or formulas of the substances to which they are converted in the interior of the catalytic converter. (15) 2006 (a) (b) (c) (d) (e) Question7 DEFINE: minimum energy required for colliding particles (molecules) to react / minimum energy required for effective collisions between particles (molecules) [Accept ‘energy needed for colliding particles to initiate reaction’. Do not accept Ea diagram] [Allow (3) for ‘energy required for reaction to take place’] GIVE: 1st reason: increased energy of collisions (particles, molecules, reactants) (3) [Accept: more collisions (particles) reach activation energy, more collisions are effective] 2nd reason: more collisions due to increased velocity of particles (3) WHICH: first reason above (3) WHY: for same temperature rise increase in number of collisions very small compared with increase in number reaching activation energy OR leads to more (increase in) effective collisions OR more collisions reach activation energy (3) [Accept ‘helps to overcome (exceed) activation energy’] DESCR: heat known volumes of the solutions separately to a certain temperature mix, note temperature*, (3) [*Accept a stated temperature] and place reaction vessel over cross (X, mark), keeping at temperature (3) record time for cross to become invisible and take rate as 1/time (3) repeat for other temperature(s) (3) WHEN: AgNO3 and NaCl present as free ions in solution / no bond breaking(dissociation) / For Na2S2O3 and HCl covalent bonds must be broken (dissociated) [Accept ‘AgNO3 and NaCl are ionic’ or ‘Na2S2O3 and HCl are covalent’ for (3) only] TYPE: heterogeneous catalysis (3) GIVE: first entering // first converted to (2 x 3) second entering // second converted to (2 x 3) [The two substances required can both be hydrocarbons or oxides of nitrogen.] Entering Converted to Carbon monoxide (CO) Carbon dioxide (CO2) Hydrocarbon (or named or correct formula) Carbon dioxide (CO2) & water (H2O) Oxide of nitrogen (correct formula) Accept NOx Nitrogen (N2) & oxygen (O2) [Accept nitrogen (N2) on its own] (5) (12) (6) (6) (6) (15)
  4. 4. 2007 Question 9 (a) Define the rate of a chemical reaction. Why does the rate of chemical reactions generally decrease with time? (8) 3 (b) The rate of reaction between an excess of marble chips (CaCO3) (diameter 11 – 15 mm) and 50 cm of 20 M hydrochloric acid was monitored by measuring the mass of carbon dioxide produced. The table shows the total mass of carbon dioxide gas produced at stated intervals over 9 minutes. Plot a graph of the mass of carbon dioxide produced versus time. (12) Use the graph to determine (i) the instantaneous rate of reaction in grams per minute at 4.0 minutes, (ii) the instantaneous rate of reaction at this time in moles per minute. (9) (c) Describe and explain the effect on the rate of reaction of repeating the experiment using 50 cm 3 of 1.0 M hydrochloric acid and the same mass of the same size marble chips. (6) (d) Particle size has a critical effect on the rate of a chemical reaction. (i) Mark clearly on your graph the approximate curve you would expect to plot if the experiment were repeated using 50 cm3 of 2.0 M HCl and using the same mass of marble chips but this time with a diameter range of 1 – 5 mm. (6) (ii) Dust explosions present a risk in industry. Give three conditions necessary for a dust explosion to occur. (9) 2007 Question 9 (a) (b) (i) (ii ) (c) (d) (i) (ii ) DEFINE: change* in concentration per unit time / [* “increase” or “decrease” not acceptable for “change”] [Accept ‘mass’ or ‘amount’, but not ‘volume’ or ‘quantity’, for ‘concentration’] WHY: concentration(s) decrease [reactant(s) used up] PLOT: labelled and scaled axes [Accept ‘time’ or ‘minutes’; ‘mass’ or ‘grams’] (3) all points plotted correctly (6) [Allow (3) if six points are correctly plotted; assume (0, 0) is correct] curve drawn [has to be drawn to (0, 0)] (3) Note: award (6) for plotted correctly only if graph paper is used, otherwise 0. USE 0.20 – 0.26 g min–1 [allow 3 marks for good tangent or 3 marks for calculation based on data points from candidate’s tangent] 0.004 – 0.006 mol min–1 DESCRIBE: slower rate (3) EXPLAIN: acid less concentrated OR rate decreases with concentration (3) MARK: see candidate’s graph* [steeper at start; levels off sooner; reaches same height] (6) [Allow (3) if description is fully correct but not shown on the graph] [Allow (3) if two of the three conditions above are shown on the graph] * not necessarily on graph paper DUST: combustible dust particles // dryness // above certain concentration // source of ignition // oxygen (air)* // enclosed space ANY THREE: (3 x 3) [*Can be picked out of description if clear that it is a condition.] [Allow “build up” or “enough of dust” or “spread out” for “certain concentration”.] [Allow “lack of ventilation” for “enclosed space”] [Do not accept “heat” for “ignition source”] (4) (12) (6) (3) (6) (6) (9) 2008 Question 3. (a) Hydrogen peroxide solution is an oxidising reagent. Draw or describe the warning symbol put on a container of hydrogen peroxide solution to indicate this hazard. (5) (b) Write a balanced equation for the decomposition of hydrogen peroxide. (6) (c) Solid manganese(IV) oxide catalyst was added to a hydrogen peroxide solution at a time known exactly and the rate of production of gas was monitored as the hydrogen peroxide decomposed. Draw a labelled diagram of an apparatus that could be used to carry out this experiment. (12) (d) The table shows the volumes of gas (at room temperature and pressure) produced at intervals over 12 minutes. (4)
  5. 5. Plot a graph of the volume of gas produced versus time. Explain why the graph is steepest at the beginning. (15) (e) Use your graph to (i) determine the instantaneous rate of gas production at 5 minutes, (ii) calculate the total mass of gas produced in this experiment. 2008 Question 3 (a) (b) (c) (d) (e) (i) (ii) 2009 (12) DRAW: circle with flames rising WRITE: H2O2 → H2O + 1/2O2 / 2H2O2 → 2H2O + O2 FORMULA: (3) BALANCING: (3) DRAW: apparatus with hydrogen peroxide and catalyst separate (3) arrangement for mixing at a precise time (6) Completely unlabelled diagram (– 3) graduated cylinder over water (3) PLOT: axes accurately labelled with numbers // axes with correctly labelled units // eight points accurately plotted // curve accurately drawn from origin (4 x 3) Note: If not on graph paper, accuracy must be checked with ruler. EXPLAIN: greatest rate OR highest concentration of H2O2 OR most collisions (3) [Accept “rate decreases”. Do not accept “amount” for “concentration”.] see graph 4.0 – 6.0 cm3 min–1 (from correctly drawn tangent) (6) [Allow 3 marks for tangent drawn at 5 minutes] 0.104 g [Accept 0.1] (6) 78 ÷ 1000 ÷ 24 = 0.00325 mol (3) × 32 = 0.104 (3) (5) (6) (9) (15) (6) (6) Question 9 (a) Explain (i) activation energy, (ii) effective collision. (8) The effect of temperature on the rate of a chemical reaction was investigated using dilute solutions of hydrochloric acid and sodium thiosulfate. Suitable volumes and concentrations of the solutions were used. The reaction is represented by the following balanced equation. 2HCl + Na2S2O3 → 2NaCl + H2O + S + SO2 Describe how the time for the reaction between the solutions of hydrochloric acid and sodium thiosulfate was obtained at room temperature. (6) In a reaction mixture what effect, if any, does an increase in temperature of 10 K have on each of the following: (i) the number of collisions, (ii) the effectiveness of the collisions, (iii) the activation energy. (9) (b) The catalytic oxidation of methanol using platinum wire is illustrated in the diagram. State one observation made during the experiment. Name any two products of the oxidation reaction. What type of catalysis is involved in this reaction? (12) Explain one way in which the presence of the platinum catalyst speeds up the oxidation of the hot methanol. Explain how a catalyst poison interferes with this type of catalysis. (9) Give another example of a reaction which involves the same type of catalysis, indicating clearly the reactant(s) and the catalyst. (6)
  6. 6. 2009 (a) Question 9 (i) (ii) (i) (ii) (iii ) (b) EXPLAIN: minimum energy required for colliding particles (molecules) to react / minimum energy needed for effective collisions between particles (molecules) (5) [Allow (3) for ‘energy (required) for reaction to take place’] [Do not accept EAct diagram] reaches activation energy / results in reaction between colliding particles / results in product (3) DESCRIBE: mix and start clock (3) note time when cross cant be seen through the solution. (3) EFFECT: small (slight, tiny, < 5 %) increase (3) EFFECT: large (big, substantial, > 50 %) increase in effective collisions (3) EFFECT: no effect / none (3) STATE: wire (Pt) glows / flame / popping sound / odour of methanal (3) NAME: methanal // hydrogen // water [Accept “carbon monoxide”] ANY TWO: (2 x 3) TYPE: heterogeneous / surface [Accept “surface adsorption (absorption)” but not “hetero”] (3) EXPLAIN: lowers activation energy / reactants adsorbed / reactants brought closer on surface / higher concentration on surface / reactants occupy active sites on surface / bond stretching / reactant oriented correctly for reaction / activated complex formed on surface of catalyst. (6) POISON: preferentially adsorbed (chemically attached) on catalyst / blocks active sites / forms bond(s) with catalyst, preventing other reaction(s) (3) GIVE: reactant(s) (3) catalyst (3) Hydrogen peroxide (H2O2) Manganese(IV) oxide (manganese dioxide, MnO2) Nitrogen (N2) & Hydrogen (H2) Iron (Fe) / Iron(III) oxide (Fe2O3) Sulfur dioxide (SO2) & oxygen (O2) Vanadium(V) oxide (V2O5) Ammonia (NH3) & oxygen (O2) Platinum/rhodium (Pt/Rh) Ethanol (C2H5OH) Aluminium oxide (Al2O3) Ethanol (C2H5OH) Platinum (Pt) Copper (Cu) / Nickel (Ni) Hydrogen (H2) & Oxygen (O2) Platinum (Pt) Name/formula of cat. converter reactant Platinum (Pt) / Palladium (Pd) / Rhodium Rh [Reactant and wrong catalyst (3) Reactant no catalyst: Award (3) for the reactant if normally catalysed.] (5) (9) (3) (3) (3) (27)
  7. 7. 2009 (a) Question 9 (i) (ii) (i) (ii) (iii ) (b) EXPLAIN: minimum energy required for colliding particles (molecules) to react / minimum energy needed for effective collisions between particles (molecules) (5) [Allow (3) for ‘energy (required) for reaction to take place’] [Do not accept EAct diagram] reaches activation energy / results in reaction between colliding particles / results in product (3) DESCRIBE: mix and start clock (3) note time when cross cant be seen through the solution. (3) EFFECT: small (slight, tiny, < 5 %) increase (3) EFFECT: large (big, substantial, > 50 %) increase in effective collisions (3) EFFECT: no effect / none (3) STATE: wire (Pt) glows / flame / popping sound / odour of methanal (3) NAME: methanal // hydrogen // water [Accept “carbon monoxide”] ANY TWO: (2 x 3) TYPE: heterogeneous / surface [Accept “surface adsorption (absorption)” but not “hetero”] (3) EXPLAIN: lowers activation energy / reactants adsorbed / reactants brought closer on surface / higher concentration on surface / reactants occupy active sites on surface / bond stretching / reactant oriented correctly for reaction / activated complex formed on surface of catalyst. (6) POISON: preferentially adsorbed (chemically attached) on catalyst / blocks active sites / forms bond(s) with catalyst, preventing other reaction(s) (3) GIVE: reactant(s) (3) catalyst (3) Hydrogen peroxide (H2O2) Manganese(IV) oxide (manganese dioxide, MnO2) Nitrogen (N2) & Hydrogen (H2) Iron (Fe) / Iron(III) oxide (Fe2O3) Sulfur dioxide (SO2) & oxygen (O2) Vanadium(V) oxide (V2O5) Ammonia (NH3) & oxygen (O2) Platinum/rhodium (Pt/Rh) Ethanol (C2H5OH) Aluminium oxide (Al2O3) Ethanol (C2H5OH) Platinum (Pt) Copper (Cu) / Nickel (Ni) Hydrogen (H2) & Oxygen (O2) Platinum (Pt) Name/formula of cat. converter reactant Platinum (Pt) / Palladium (Pd) / Rhodium Rh [Reactant and wrong catalyst (3) Reactant no catalyst: Award (3) for the reactant if normally catalysed.] (5) (9) (3) (3) (3) (27)

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