1. A. Define the term rate of reaction. The measure of the amount of reactants being converted into products per unit amount of time

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1 Name answer key period IB topic 6 Kinetics 1. A. Define the term rate of reaction. The measure of the amount of reactants being converted into products per unit amount of time b. the reaction between C and D is slow at room temperature. i. suggest two reasons why the reaction is slow at room temperature. High activation energy, incorrect collision geometry, infrequent collisions ii. a relatively small increase in temperature causes a relatively large increase in the rate of this reaction. State two reasons for this. More energetic collisions, more frequent collisions iii. suggest two ways of increasing the reaction between C and D other than increasing the temperature. Add a catalyst, increase the total pressure by decreasing the volume of the container, increase the concentration of C or D 2. What are some ways that we can measure the rate of a reaction? Measure the change in volume of gas produced, measure the change in mass, measure changes in transmission of light, measure the change in concentration using a titration, measure the change in concentration using conductivity, 3. Describe the collision theory For a reaction to occur, reactants need to collide with enough energy (activation energy) and with the correct orientation 4. Which statement is correct for collision between reactant particles leading to a reaction? a. Colliding particles must have different energy b. All reactant particles must have the same energy c. Colliding particles must have a kinetic energy higher than the activation energy d. Colliding particles must have the same velocity 5. Describe the effect of a catalyst on a chemical reaction. A catalyst speeds up a reaction by lowering the activation energy 6. Define the term activation energy Minimum amount of energy which particles must have before they are able to react 7. It is found that a 10 o C increase in temperature roughly doubles the rate of many chemical reactions. If a reaction takes 20 seconds at 40 o C, how long would it take at 60 o C? 5 seconds 8. Use the collision theory to explain why each factor (temperature, concentration, pressure, particle size) alters the rate of a reaction. Temperature- reacts hit with more energy and more frequently Concentration- more collisions will occur Pressure- more collisions will occur Particle size- more collisions will occur 9. It has been found that rates are more rapid at the beginning of a reaction than toward the end, assuming the temperature is constant. Explain why. As a reaction proceeds, the amount of reactants decrease (concentration decreases) so the reaction slows down.

2 10. Which change of condition will decrease the rate of the reaction between excess zinc granules and dilute hydrochloric acid? a. Increasing the amount of zinc b. Increasing the concentration of acid c. Pulverizing the zinc granules into powder d. Decreasing the temperature 11. Would you expect a packet of sugar to dissolve faster in hot tea or iced tea? Hot tea 12. For each of the following pairs, choose the substance or process you would expect to react more rapidly. a. Granulated sugar or powdered sugar b. Zinc in HCl at 298 K or zinc in HCl at 410 K c. 5 g of thick platinum wire or 5 g of thin platinum wire 13. Explain why there is a danger of explosion in places such as coal mines, saw mills, and grain elevators, were large amounts of dry, powdered combustible materials are present. There is high surface area of the combustible material so a reaction can occur faster 14. For each energy diagram below, label reactants, products, H, E a, and tell if it is endothermic or exothermic. See in class 15. How would each of the energy diagrams in the previous problem change if a catalyst were added to the reaction? (show using dashed lines) see in classs 16. Catalytic converters are now used in most cars to convert some components of exhaust gases into les environmentally damaging molecules. One of these reactions converts carbon monoxide and nitrogen monoxide into carbon dioxide and nitrogen. The catalyst usually consists of metals such as platinum or rhodium. a. Write an equation for this reaction. 2CO + 2NO 2CO 2 + N 2 b. Explain why it is important to reduce the concentrations of carbon monoxide and nitrogen monoxide released into the atmosphere. CO is a toxic gas and NO contributes to acid rain and forms smog c. Why do you think the converter sometimes consists of small ceramic beads coated with the catalyst? This increase the surface area of the catalyst in contact with the gas so it will increase efeciency.

3 d. Suggest why the converter usually does not work effectively until the car engine has warmed up. Catalytic behavior depends on the catalyst interacting with gases, leading to a reaction at its surface. With increasing temperatures, the increased kinetic energy of the gases allows them to collide with the catalyst more quickly. e. Discuss whether the use of catalytic converters in cars solves the problem of car pollution. They have helped but are not effective when the engine is cold so they don t remove it completely. There are some gases that are not removed by the catalyst and they produce CO 2 which is a green house gas. 17. For a given reaction, why does the rate of reaction increase when the concentration of the reactants are increased? a. The frequency of the molecular collision increase b. The activation energy increases c. The average kinetic energy of the molecules increases d. The rate constant increases 18. Based on the definition for rate of reaction, which units are used for rates? a. Mol dm -3 b. Mol time -1 c. Dm 3 time -1 d. Mol dm -3 time Curve X on the graph below shows that volume of oxygen formed during the catalytic decomposition of a 1.0 mol dm -3 solution of hydrogen peroxide: 2H 2 O 2 (aq) O 2 (g) + 2H 2 O(l) Which change would produce curve Y? a. Adding water b. adding some 0.1 mol dm -3 hydrogen peroxide solution b. Using a different catalyst d. lowering the temperature 20. The figure below shows a Maxwell-Boltzmann distribution curve for a sample of a gas at two different temperatures, T1 and T2. a. Deduce the relative values of T1 and T2. T2 > T1 b. Make reference to your answer in (a) to explain the differences in the shape of the two graphs. At higher temperature a greater proportion of particles have higher values of KE. Maxwell Boltzmann distributions shift to the right with increasing temperature as the average kinetic energy of the particles increases. At higher temperature the particles therefore have a larger spread of values for kinetic energy, although the area under the two curves remains the same when the number of particles in the sample is constant. c. A catalyst provides a reaction route with a lower activation energy, and so increases the rate of reaction Justify this statement by means of a suitably labeled Maxwell-Boltzmann distribution curve, showing the proportion of reacting particles with and without a catalyst. With a catalyst a greater proportion of particles have KE > Ea and can react. The catalyst provides an alternative route for the reaction that has a lower activation energy, Ea. This means that without increasing the temperature, a higher proportion of particles in the presence of the catalyst have sufficient energy (KE > Ea ) to react and so the rate is increased. d. Explain why catalysts increase the rate of reaction but have no effect on: i. The enthalpy change The effect of catalysts on the rate of reaction does not change the energy difference between reactants and products, H

4 ii. The stoichiometric yield of product The effect of catalysts on the rate of reaction does not change how much product is made 21. Zn (s) + CuSO 4(aq) Cu (s) + ZnSO 4(aq) Which of the following factors will increase the rate of this reaction? I. Increasing the concentration of copper sulfate II. III. Decreasing the size of the zinc pieces Carrying out the reaction at high temperature a. I and II b. I and III c. II only d. I, II, and III Review: 22. What is the concentration of nitric acid if 15 cm 3 of it is titrated with 25 cm 3 of 0.67 mol dm -3 aluminum hydroxide? 3.35 mol dm The heat of solution for silver nitrate is kj/mol. a. Is dissolving silver nitrate endothermic or exothermic? endothermic b. As silver nitrate dissolves, what change occurs in the temperature of the solution? decreases c. Is silver nitrate more likely to dissolve in oil (nonpolar) or water (polar)? Water 24. What is the concentration of a solution if 40.3 g of potassium cyanide are dissolved 450 cm 3 of solution? 1.4 mol dm How many grams of sodium hydroxide are in 210 cm 3 of a 0.67 mol dm -3 solution? 5.6 g 26. How do gases compare with liquids and solids in terms of distance between their molecules? Gas molecules are much farther apart 27. Which of the following gases would have the greatest kinetic energy, He at 20 C or He at 50 C? 28. What is sublimation? Is it endothermic or exothermic? Changing a solid to a gas; endothermic 29. Is melting endothermic or exothermic? Endothermic 30. Is condensation endothermic or exothermic? Exothermic 31. Label each of the following as exothermic or endothermic and tell if the temperature would increase or decrease when the reaction occurs. a. 2H 2 + O 2 2 H 2 O H = kj endothermic; decrease b. 2NO N 2 + O 2 H = kj exothermic; increase 32. What type of intermolecular forces does each of the following have?

5 a. CH 4 b. NH 3 c. H 2 O d. H 2 S van der waals hydrogen bonding hydrogen bonding dipole-dipole 33. Which of the following molecules in the previous question would have the lowest boiling point? CH If 6.5 moles of hydrogen reacts with silver phosphate, how many grams of silver will be produced? 1400 g Ag 35. If M represents a group 1 metal, what is the formula for the compound formed by M and oxygen? a. MO 2 b. M 2 O c. M 2 O 3 d. M 3 O When do electrons release photons(packets of energy)? When the electrons: a. move to higher levels of energy b. return to their original energy level c increase orbital speed around the nucleus d. are released by the atom 37. Which of the following elements has the strongest attraction for electrons? a. boron b. aluminum c. oxygen d. sulfur 38. As the elements in Group 17 are considered in order of increasing atomic number, the chemical reactivity of each successive element: 39. a. decreases b. increases c. remains the same