Answer Key. Chapter 18: Kinetics. 18.1 Chemical Reaction Rate. Practice. Questions. Read the material at the link below and answer the following quest...
CK-12 Chemistry Concepts - Intermediate Answer Key Chapter 18: Kinetics 18.1 Chemical Reaction Rate Practice Questions Read the material at the link below and answer the following questions: http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Reaction_Rates/Reaction_Rat e 1. Why is the rate of disappearance a negative value? 2. What is the average rate of reaction? 3. What is the instantaneous rate of reaction? Answers 1. The concentration of reactant is decreasing. 2. Change in concentration over a time period. 3. Instantaneous change in concentration over a very small time period. Review Questions 1. What is another word for rate? 2. What does [ ] stand for? 3. What are the units of reaction rate? Answers 1. Speed. 2. Molar concentration. 3. Molarity/second.
18.2 Collision Theory Practice Questions 1
Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=4n_hKAA87nM 1. What were the reactants? 2. What was the product? 3. What did the match do? Answers 1. Hydrogen and oxygen. 2. Water. 3. Make the molecules collide faster. Review Questions 1. How does a chemical reaction occur? 2. What are two requirements for collision to form a product? 3. Two molecules collide and then bounce off of one another. What kind of collision is that? Answers 1. Molecules collide. 2. Enough kinetic energy and proper orientation. 3. Ineffective collision.
18.3 Activation Energy Practice Watch the video at the link below and answer the questions: http://www.youtube.com/watch?v=u_1uLP30uxY 1. Does magnesium react with water at room temperature? 2. How did the speaker get magnesium to react with water? 3. What is one product of this reaction? Answers Answers are given on the web site. Review Questions 2
1. Does sodium react faster or slower with water than calcium does? 2. How does vibrational energy contribute to a reaction? 3. Before some molecules react, what has to happen? Answers 1. Faster. 2. Bonds will break if enough vibrational energy is present. 3. They have to be heated to increase the kinetic energy of the particles.
18.4 Potential Energy Diagrams Practice Questions Do problems 1-9 at the following link: http://www.foothillfalcons.org/ourpages/auto/2011/3/8/39370464/PotEnergyDiagWS.pdf Answers Answers are found at the following web site: http://www.foothillfalcons.org/ourpages/auto/2011/3/23/67987860/PotEDiagWS_other% 20worksheetKEY.pdf Review Questions 1. In an endothermic reaction, is the potential energy of the products higher or lower that the potential energy of the reactants? 2. In an exothermic reaction, is the potential energy of the products higher or lower that the potential energy of the reactants? 3. What does activation energy tell us? Answers 1. Higher. 2. Lower. 3. How fast the reaction will proceed.
18.5 Activated Complex 3
Practice Questions Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=rl50M-wNVcs 1. 2. 3. 4. 5.
What were the reactants? What colors were the reactants? What color was the activated complex? What were the structures of the products? What color was the final solution?
Answers 1. 2. 3. 4. 5.
A-A and B-B A-A was pink and B-B was yellow. Green 2 A-B. Pink again.
Review Questions 1. Do all collisions of reactant particles lead to products? 2. How long does the activated complex usually last? 3. How does this compare with the activated complex in the video you watched? Answers 1. No, some go back to reactants. 2. A very short period of time, often 10 -13 seconds. 3. Very fast, the video activated complex remained in existence for several seconds.
18.6 Factors Affecting Reaction Rate Practice Questions Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=UWkzS-HaxZE 4
1. What factor was demonstrated by adding oxygen to the fire? 2. What was shown with the aluminum powder? 3. What factor was mentioned, but not demonstrated? Answers 1. Increase in concentration. 2. Increase in surface area. 3. Temperature. Review Questions 1. How does an increase in concentration of reactant increase rate? 2. Why would rates increase with a larger surface area of reactants? 3. What effect does temperature have on reaction rate? Answers 1. More molecules to collide with one another. 2. Larger surface area means more collisions per unit time. 3. Increase in collision velocity.
18.7 Catalysts Practice Questions Watch the video at the link below and answer the following questions: http://www.youtube.com/watch?v=9KQdF1bnXHE 1. What dye is used on blue jeans? 2. What do enzymes do for the blue jeans? 3. List three issues that exist for uncatalyzed reactions. Answers 1. Indigo 2. Fade the blue jeans. 3. The reaction may be slow, require heat, and have unwanted by-products. Review Questions 5
1. What does a catalyst affect in a chemical reaction? 2. Is the ΔH for the process affected? 3. When writing a chemical equation, where do we indicate the catalyst? Answers 1. It lowers the activation energy. 2. No. 3. Above the arrow.
18.8 Rate Law and Specific Rate Constant Practice Questions Read the material at the link below and answer the following questions: http://www.differencebetween.com/difference-between-reaction-rate-and-vs-specificrate-constant/ 1. Why is the sign for reactant concentration negative? 2. Why is the sign for product concentration positive? 3. What do the lower-case letters in the rate equation represent? Answers 1. The reactant concentration is decreasing. 2. The product concentration is increasing. 3. The stoichiometric coefficients for reactants and products. Review Questions 1. What is a rate law? 2. What is a specific rate constant? 3. How are these parameters determined? Answers 1. It shows the relationship of reaction rate to concentration. 2. A constant that related rate of reaction to concentration. 3. They need to be determined experimentally.
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18.9 Order of Reaction Practice Questions Read the material at the link below and answer the following questions: 1. What is a zero-order reaction? 2. What is a second-order reaction? 3. How is the order of a two-reactant reaction determined? Answers 1. The reaction rate is independent of concentration. 2. The rate is dependent on the square of the concentration. 3. The order is the sum of the exponents for the two reactants. Review Questions 1. What is a first-order reaction? 2. How is the instantaneous rate determined? 3. How do we determine rate law and reaction order? Answers 1. The rate is dependent on the concentration of the reactant. 2. By the slope of the tangent to the curve at that time. 3. Experimentally.
18.10 Determining the Rate Law from Experimental Data Practice Questions Use the site below to practice determination of rate constant with experimental data. http://ibchem.com/IB/ibnotes/full/kin_htm/order_calculation.htm Answers Answers are provided at the site.
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Review Questions 1. How do you carry out experiments for determining rate constants? 2. Why is the reaction order with regard to NO a value of 2? 3. Why is the reaction order with regard to hydrogen value of 1? Answers 1. Vary the concentration of one reactant while holding the other constant. 2. The rate quadrupled when [NO] was doubled. 3. The rate doubled when [H2] was doubled.
18.11 Reaction Mechanisms and the Elementary Step Practice Questions Read the material at the web site below and answer the following questions: http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Rate_Laws/Reaction_Mechani sms/Reaction_Mechanisms 1. Will kinetics allow us always to determine the mechanism of a particular reaction? 2. What must a reaction mechanism tell us? 3. What is a unimolecular elementary process? 4. What is a bimolecular elementary process? Answers 1. 2. 3. 4.
No, kinetics often will not. What occurs at each step of the reaction. When a single molecule dissociates. When two molecules collide.
Review Questions 1. Do chemical reactions usually occur in a single step? 2. What does the overall balanced equation not tell us? 3. How do overall reactions usually proceed? 8
Answers 1. No, they rarely do. 2. The steps in the reaction process. 3. By a series of small steps. 18.12 Reaction Intermediate Practice Questions Read the material at the link below and answer the questions at the end: http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Rate_Laws/Reaction_Mechani sms/Reaction_Mechanisms Answers Answers are on the web site. Review Questions 1. 2. 3. 4.
What is the intermediate in the reaction described above? Do we see this intermediate in the actual reaction mix? Where do we first see an intermediate in a reaction mechanism? What happens to the intermediate?
Answers 1. 2. 3. 4.
N2O2. Yes, it has been detected. In an early step. It is consumed in a later step.
18.13 Molecularity Practice Questions Do the molecularity parts of problems 4 and 5 at the link below: 9
http://faculty.scottsdalecc.edu/borick/files/2011/05/8-30HW.pdf Answers Answers are given at the web site. Review Questions 1. What is a unimolecular reaction? 2. What is a bimolecular reaction? 3. Why are termolecular reactions rare? Answers 1. One molecule involved in an elementary step. 2. Two molecules involved in an elementary step. 3. Simultaneous collisions with three molecules is very unlikely. 18.14 Rate-Determining Step Practice Questions Read the material at the link below and work the practice problem: http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Rate_Laws/Reactions/RateDetermining_Step Answers The answer is on the website.
Review Questions 1. What is the rate-limiting step in a reaction? 2. Can we determine the rate-limiting step simply by looking at the reaction mechanism?
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3. In the hydrogen peroxide example above, why was step 1 determined to be the rate-limiting step? Answers 1. The slowest step in the process. 2. No, we must test the kinetics experimentally. 3. The rate law for step one agreed with the experimentally determined rate law for the overall reaction.
18.15 Mechanisms and Potential Energy Diagrams Practice Questions View the section on two-step reactions at the site below and then do the self-test (both buttons are at the top of the slide). Don’t worry about ΔG – just consider it an indication of activation energy as is ΔE in the diagram above. http://www.wfu.edu/chem/courses/energydiagram/index.html Answers Answers are given at the site. Review Questions 1. What does a potential energy diagram tell us? 2. In the diagram above, which step has the highest activation energy? 3. If a catalyst lowered the step one activation energy to a value lower than the step two activation energy, which step would be rate-limiting? Answers 1. The activation energies for the reaction. 2. Step one. 3. Step two because it would now have the higher activation energy.