Beatty 3.1 ROR (W1) 2023 Answers

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: _______________ Class: 4E___ TOPIC: SPEED / RATE OF REACTION (WORKSHEET 1) – FACTORS Learning Objectives: (a) Describe the effect of concentration, pressure, particle size and temperature on the speeds of reactions and explain these effects in terms of collisions between reacting particles. (b) Define the term cata lyst and describe the effect of catalysts (including enzymes) on the speeds of reactions. (c) Explain how pathways with lower activation energies account for the increase in speeds of reactions. (d) State that some compounds act as catalysts in a range of industrial processes and that enzymes are biological catalysts. Multiple-Choice Questions 1 Which factor does not affect the speed of a chemical reaction? A concentration of reactant B colour of reactant C surface area of reactant D temperature of reactant ( B ) 2 Which solution would react the fastest if added to the same amount of magnesium? A 4 g of acid in 50 cm3 of water B 10 g of acid in 100 cm3 of water C 40 g of acid in 250 cm3 of water D 100 g of acid in 1000 cm3 of water ( C ) 3 Which statement best explains why coal dust forms an explosive mixture with air? A Coal dust catalyses the explosion. B Coal dust has a large surface area. C Crushing coal breaks chemical bonds. D Crushing coal releases hydrogen from compounds in coal. ( B ) 4 Dilute sulfuric acid reacts with copper(II) oxide to form copper(II) sulfate and water. What would not alter the rate of reaction? A The concentration of the sulfuric acid. B The pressure at which the reaction takes place. C The size of the particles of copper(II) oxide. D The temperature of the reacting mixture. ( B )

2 5 A teacher wanted to demonstrate a reaction between an acid and a soli d reactant, but it was too violent to be safe. Which of these changes would make the reaction safer to demonstrate? acid temperature acid concentration size of solid reactant A lower lower larger B lower lower smaller C higher higher larger D higher higher smaller ( A ) 6 Which reaction is the fastest? ( D ) 7 Which factor decreases the activation energy of a reaction? A addition of a catalyst B increase in concentration of reactants C increase in pressure D increase in temperature ( A ) 8 The oxide of an element J increases the rate of decomposition of hydrogen peroxide. At the end of the reaction the oxide J is chemically unchanged. Which details are those of J? proton number mass number A 18 40 B 20 40 C 25 55 D 53 127 ( C )

3 9 The enthalpy diagram shows an uncatalysed, exothermic reaction. The reaction was repeated in the presence of a catalyst. What effect does the catalyst have on the activation energy, Ea, and the enthalpy change, ∆H? Ea ∆H A decreases decreases B decreases unchanged C increases increases D unchanged decreases ( B ) 10 In the reaction between zinc and hydrochloric acid, the following changes could be made to the conditions. 1 increase in concentration of acid 2 increase in particle size of the zinc 3 increase in pressure on the system 4 increase in temperature of the system Which pair of changes will increase the rate of reaction? A 1 and 2 B 1 and 4 C 2 and 3 D 3 and 4 ( B ) Structured Questions 11 Using knowledge of reacting particles, explain each of the observations. (a) Nitrogen reacts more vigorously with hydrogen at pressures above 200 atm than at 1 atm. As the pressure increases, the nitrogen and hydrogen molecules are forced closer together in a smaller volume and the number of particles per unit volume increases. As such, the particles collide more frequently and the frequency of effective collisions increases, increasing the rate of reaction.

4 (b) Placing a light stick in warm water makes it glow more brightly. As the temperature increases in warm water , the reacting particles in the light stick gain more kinetic energy and the particles move faster, colliding more frequently. As such, there is an increase in the number of react ing particles colliding with energy equals to or greater than activation energy and the frequency of effective collisions increases, increasing the rate of reaction. This causes the light stick to glow more brightly. (c) When a piece of raw liver is dropped into hydrogen peroxide, there is rapid reaction and oxygen gas is liberated. The enzymes present in liver act as biological catalysts to provide an alternative reaction pathway with a lower activation energy than the uncatalysed reaction. As such, there is an increase in the number of reacting particles colliding with energy equals to or greater than activation energy and the frequency of effective collisions increases, increasing the rate of reaction of the decomposition of hydrogen peroxide. 12 A student c arried out a series of experiments to measure the time it took for an indigestion tablet to react completely with mixtures of hydrochloric acid and water. Her results are tabled below. experiment number volumes mixed / cm3 temperature at start / °C time taken to react completely / s acid water acid + water crushed tablet whole tablet 1 10 50 19 34 39 2 20 40 20 28 33 3 30 30 28 18 24 4 30 30 20 24 28 5 20 40 19 28 32 6 10 50 29 28 32 (a) Explain how the student would know that the reaction between the tablet and acid has been completed. The reaction has been completed when the tablet has dissolved completely. (b) Explain why the total volume of the acid -water mixture was kept constant in all the experiments. This is to ensure that the volume of the s olution used is constant, so that the concentration of the acid in each experiment is proportional to the volume of acid used.

5 (c) Use the data in the table to explain whether the speed of the reaction between the acid and the tablets was increased, remained the same or decreased by (i) crushing the tablet, speed of reaction: increased explanation Comparing all experiments between the time taken for the crushed tablet and the time taken for the whole tablet, the time taken for the crushed tablet is about 4 to 5s shorter than the whole tablet. This can be seen from Experiment 1 that the time taken is 34s for crushed tablet, whereas for the whole tablet is 39s. (ii) increasing the temperature of mixture, speed of reaction: increased explanation Comparing Experiments 1 and 6 as well as 3 and 4, the time taken for complete reaction is shorter in the experiment with the higher temperature (Experiment 6 of 28s at 29 °C compared to Experiment 1 of 34s at 19 °C, Experiment 4 of 24s at 20 °C compared to Experiment 3 of 18 s at 28 °C). A shorter time taken would imply a faster rate of reaction. (iii) increasing the concentration of the acid, speed of reaction: increased explanation Comparing Experiments 1 and 5 as well as 2 and 4, the time taken for complete reaction is shorter in the experiment with the higher concentration of acid (Experiment 5 of 28 s using 20 cm 3 of acid compared to Experiment 1 of 34 s using 10 cm 3 of acid, Experiment 4 of 24 s using 30 cm 3 of acid compared to Experiment 2 of 28 s using 20 cm 3 of acid). A s horter time taken would imply a faster rate of reaction. (d) How would you recommend that these tablets be taken so as to give the quickest relief from an acid stomach? These tablets should be crushed to ensure a larger surface area to quicken the relief from a