Beatty 15.3 ROR REVIEW(W3) 2023 Answers

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: _______________ Class: 4E___ TOPIC: SPEED / RATE OF REACTION REVIEW (WORKSHEET 3) Multiple-Choice Questions 1 Two gases Q and R react according to the equation. Q (g) + R (g) → T (g) The reaction mixture is placed in a container at room temperature. Which action can speed up the formation of gas T? A Adding an inert gas to the mixture. B Using a bigger container. C Lowering the piston in the container. D Placing the container in water at 5 °C. ( C ) 2 Catalase is an enzyme commonly found in living cells. It increases the rate of decomposition of hydrogen peroxide found in human bodies into water and oxygen gas. Which statement about catalase is correct? A It operates effectively at all temperatures. B It operates most effectively over a certain range of pH. C It increases the activation energy of the decomposition of hydrogen peroxide. D It increases the yield of products from the decomposition of hydrogen peroxide. ( B ) 3 Hydrogen peroxide is catalytically decomposed by manganese( IV) oxide. To study the effect of the concentration of the solutions on the rate of reaction, the total volume of oxygen evolved was recorded against time. Three experiments were performed with a fixed mass of catalyst but with (i) 50 cm3 of 2.0 mol/dm3 hydrogen peroxide (ii) 100 cm3 of 1.0 mol/dm3 hydrogen peroxide (iii) 100 cm3 of 2.0 mol/dm3 hydrogen peroxide On the graph above, which of the curves X, Y, Z relate to the solutions (i), (ii), (iii)? (i) (ii) (iii) A X Y Z B X Z Y C Z X Y D Y Z X ( D ) mixture of Q and R

2 4 Calcium carbonate was reacted with an excess of dilute hydrochloric acid at room temperature. CaCO3 + 2HCl → CaCl2 + H2O + CO2 Two experiments were carried out. Experiment 1: 100 g of calcium carbonate in large lumps. Experiment 2: 50 g of calcium carbonate as a fine powder. Which graph is correct? ( D ) 5 A student investigated the rate of reaction of marble chips with excess dilute hydrochlor ic acid, by measuring the change in mass over a period of time. The experiment was then repeated using powdered calcium carbonate. How did the initial rate and the final mass change when powdered calcium carbonate was used? initial rate final mass A faster lesser B faster unchanged C slower unchanged D unchanged unchanged ( B ) 6 In the Contact Process, traces of vanadium( V) oxide is added in the oxidation of sulfur dioxide to sulfur trioxide in the equation as shown. 2SO2 + O2 ⇌ 2SO3 Which statement(s) correctly explain(s) why vanadium(V) oxide is added? 1 It acts as an oxidising agent to oxidise sulfur dioxide. 2 It ensures that the yield would be 100%. 3 It removes acidic impurities present in the reaction. 4 It speeds up the reaction by providing an alternative reaction pathway. A 1 and 2 only B 1 and 4 only C 3 and 4 only D 4 only ( D )

3 7 Two experiments were carried out under the same conditions of temperature and pressure, reacting marble with dilute hydrochloric acid. In experiment 1, an excess of powdered marble was added to 20 cm 3 of dilute hydrochloric acid. In experiment 2, an excess of marble chips was added to 20 cm 3 of dilute hydrochloric acid of the same concentration. The total volumes of carbon dioxide given off were measured at intervals and plotted against time. Which pair of curves would be obtained in both experiments? experiment 1 experiment 2 A X Y B X Z C Y X D Y Z ( A ) 8 Curve X shows the volume of hydrog en given off when 1.0 g of granulated zinc reacts completely with excess hydrochloric acid at 30 °C. What change could produce curve Y? A use 0.5 g of granulated zinc at 40 °C B use 0.5 g of granulated zinc at 20 °C C use 1.0 g of granulated zinc at 40 °C D used 1.0 g of granulated zinc at 20 °C ( A ) 9 The energy profile diagrams show how adding a substance X to a reaction mixture changes the reaction pathway. Which change is likely to be observed when X is added to the reaction mixture? A The reaction becomes less endothermic. B The reaction becomes less exothermic. C The speed of reaction decreases. D The speed of reaction increases. ( D )

4 Structured questions 10 When carbonates of some metals are heated, they decompose to produce carbon dioxide gas. The graphs below show the results of an investigation into the thermal stability of various metal carbonates. In each experiment, 0.0100 mol of carbonate was heated to the same temperature. The volume of carbon dioxide produced was measured every minute. (a) Suggest why, at the start of each experiment, the rate of reaction was very slow. Thermal energy is absorbed to overcome the energy barrier of the activation energy. (b) Explain how y ou would tell from the graphs that the decomposition of the carbonates was not complete? The volume of carbon dioxide has not reached a constant value / is still increasing. (c) A student suggested that the same mass rather than the same number of moles of carbonates should be used to ensure a fair comparison. Do you agree with him? Explain your answer. No. Same number of moles of carbonate will yield the same volume of carbon dioxide gas for comparison. However, using the same mass of carbonate would yield different number of moles of carbonates and different volumes of gas produced due to the different molar mass of the metal carbonates. This will not be a fair comparison. (d) (i) Based on the thermal stability of the various metal carbonates, arrange the metals in order of increasing reactivity. P, Q, R, S (ii) With reference to the graphs, briefly explain your answer in (d)(i). The higher the position of the metal in the reactivity series, the greater the thermal stability of the metal carbonate. As su ch, a larger amount of heat / thermal energy is needed to decompose the carbonate, releasing lower volume of gas per unit time. (e) Sketch on the same graph, the graph expected when potassium carbonate is heated.

5 11 An experiment was carried out to measure th e rate of reaction between excess powdered calcium carbonate and dilute acids. (a) In Experiment 1, 20 cm3 of 0.1 mol/dm3 hydrochloric acid was used. (i) Write a balanced chemical equation, with state symbols for the reaction. 2HCl(aq) + CaCO3(s) → CaCl2(aq) + H2O(l) + CO2(g) (ii) Calculate the volume of carbon dioxide made at room temperature and pressure. No of mol of acid = (20 ÷ 1000) × 0.1 = 0.00200 mol No of mol of CO2 = 0.02 ÷ 2 = 0.00100 mol Volume of CO2 = 0.01 × 24 = 0.0240 dm3 (b) A further experiment using hydrochloric acid, Experiment 2, was carried out. The results of Experiments 1 and 2 are shown on the graph. Suggest the concentration and volume of hydrochloric acid used for Experiment 2. concentration: 0.0500 mol/dm3 volume 20.0 cm3 (c) A further experiment, Experiment 3 was carried out using 20 cm 3 of 0.1 mol/dm 3 sulfuric acid. The initial rate of reaction for Experiment 3 was faster than for the other experiments but the reaction stopped suddenly after o nly a small amount of gas had been given off. (i) Name the salt formed in Experiment 3. calcium sulfate (ii) Explain why the reaction stops. Calcium sulfate is an insoluble salt and coats over calcium carbonate, preventing further reaction with the acid. (iii) Explain why the initial rate of reaction was faster than for the other reactions.

6 Sulfuric acid is a dibasic acid. For every 1 mole of sulfuric acid, 2 mol