Rates and Mechanisms of Chemical Reactions. Ch 16 of Silberberg's Principles of General Chemistry 2nd edition
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| 1066266043 | Rate of a reaction | the change in the concentration of reactant or product per unit of time | 0 | |
| 1066266044 | Every reaction has a _____ rate under a given set of conditions | specific | 1 | |
| 1066266045 | T or F: The rate of reaction changes as the reaction proceeds. | True | 2 | |
| 1066266046 | The rate depends on ______, _______ and ______ because reactants must collide to react. | temperature, concentration and physical state | 3 | |
| 1066266047 | The reaction rate is ________ at the beginning of the reaction, when the concentration is the greatest, and ______ at the end. | fastest, slowest | 4 | |
| 1066266048 | Average rate of reaction | the concentration change of a reaction over a period of time | 5 | |
| 1066266049 | instantaneous rate of reaction | the concentration change of a reaction at any instant | 6 | |
| 1066266050 | Kinetic studies typically measure _____ because products are not yet present. | initial rate | 7 | |
| 1066266051 | initial rate of reaction | the rate at the instant the reactants are mixed | 8 | |
| 1066266052 | when products are not yet present only the ____ reaction is taking place | forward | 9 | |
| 1066266053 | The rate of reaction is expressed mathematically through what? | The rate law | 10 | |
| 1066266054 | Is the rate law determined by experiment or the balanced equation? | experiment. | 11 | |
| 1066266055 | What does the rate law consists of? | a temperature - dependent rate constant, concentration terms raised to an exponent, or reaction order. | 12 | |
| 1066266056 | What does the reaction order indicate? | How the concentration of that reactant affects the rate. | 13 | |
| 1066266057 | The integrated rate law includes what as variables? | concentration and time | 14 | |
| 1066266058 | what does the integrated rate law incorporate? | the reaction order and the half-life | 15 | |
| 1066266059 | half-life | the time required for half of a reactant to be used up | 16 | |
| 1066266060 | T or F: The half-life of a first-order reaction does not depend on reactant concentration. | true | 17 | |
| 1066266061 | The temperature affects the rate of a reaction by influencing what? | The rate constant | 18 | |
| 1066266062 | molecules must have what in order to react? | the minimum energy or energy of activation, Ea, | 19 | |
| 1066266063 | what does the Arrhenius equation show? | That rate increases with temperature and decreases with Ea | 20 | |
| 1066266064 | What does the collision theory propose? | For a reaction to occur, reactant molecules must collide and the energy of the collision must exceed Ea | 21 | |
| 1066266065 | Higher temperature increases the _____ of collisions and the _____ of collisions with energy greater than Ea. | frequency, fraction | 22 | |
| 1066266066 | what is an effective collision? | when the atoms of the molecules are oriented correctly for a bind to form between them | 23 | |
| 1066266067 | transition state theory | explains that the Ea is the energy needed to form a high energy species | 24 | |
| 1066266068 | how long can high energy species exist? | only momentarily | 25 | |
| 1066266069 | what to high energy species include? | partially broken reactant bonds and partially formed product bonds | 26 | |
| 1066266070 | every step in a reaction has a what? | transition state or activated complex | 27 | |
| 1066266071 | what is proposed for the rate law of an overall reaction? | a reaction mechanism | 28 | |
| 1066266072 | what does the reaction mechanism consist of? | several elementary steps, each with its own rate law | 29 | |
| 1066266073 | to be a valid mechanism, what must be occur? | the sum of the elementary steps must give the balanced equation, the steps must be physically reasonable and the mechanism must correlate with the rate law. | 30 | |
| 1066266074 | what does a catalyst do? | speeds a reaction in both directions without being consumed. | 31 | |
| 1066266075 | how does a catalyst function? | by lowering the Ea of the rate-determining step of an alternative mechanism for the same overalll reaction | 32 | |
| 1066266076 | Do catalysts have to be in the same phase as the reactants and products? | no. catalysts can function in the same (homogeneous) or a different (heterogeneous) phase | 33 | |
| 1066266077 | what is chemical kinetics | the study of reaction rates | 34 | |
| 1066266078 | what are reaction rates | the changes in concentrations of reactants or products as a function of time | 35 | |
| 1066266079 | what is the reaction mechanism? | the steps a reaction goes through as reactant bonds are breaking and product bonds are forming | 36 | |
| 1066266080 | Under any given set of conditions, each reaction has what? | its own characteristic rate | 37 | |
| 1066266081 | how is the characteristic rate of a reaction determined? | By the chemical nature of the reactants | 38 | |
| 1066266082 | What four factors affect the rate of a given reaction | the concentrations of the reactants, the physical state of the reactants, the temperature at which the reaction occurs, and the use of a catalyst | 39 | |
| 1066266083 | why does concentration influence the rate of the reactants? | the more molecules present in the container, the more frequently they collide, and the more often a reaction between them occurs | 40 | |
| 1066266084 | reaction rate is proportional to what? | the concentration of reactants | 41 | |
| 1066266085 | why does the physical state influence the rate of the reactants? | the more finely divided a solid or liquid reactant, the greater its surface area per unit volume, the more contact it makes with the other reactant, and the faster the reaction occurs. molecules must mix to collide | 42 | |
| 1066266086 | why does the temperature influence the rate of the reactants? | molecules must collide with enough energy to react. At a higher temperature, more collisions occur in a given time. | 43 | |
| 1066266087 | temperature has a major effect on what? | the speed of a reaction | 44 | |
| 1066266088 | Temperature affects the kinetic energy of the molecules and thus the what? | The energy of the collisions | 45 | |
| 1066266089 | How does raising the temperature increase the reaction rate? | Increasing the number and the energy of the collisions | 46 | |
| 1066266090 | What is a rate? | a change in some variable per unit of time. | 47 | |
| 1066266091 | equation for the rate of motion | (change in position) / (change in time) = (x₂-x₁) / (t₂-t₁) = Δx / Δt | 48 | |
| 1066266092 | What is the reaction rate? | the changes in concentrations of reactants or products per unit time | 49 | |
| 1066266093 | T or F: Product concentrations increase when reactant products decrease. | true | 50 | |
| 1066266094 | for a forward reaction, the change in concentration of a reactant is always ______. | negative | 51 | |
| 1066266095 | For a general reaction A→B, what is the rate expressed in term of A? What are the units? | rate = - Δ[A] / Δt, moles per liter per second ( mol / Ls ) | 52 | |
| 1066266096 | For a forward reaction, the rate of the products is _____. why? | positive. the concentration is increasing over time. | 53 | |
| 1066266097 | The rate of a real chemical reaction _____ over time as the reaction proceeds. | varies | 54 | |
| 1066266098 | Average rate | the rate of a reaction over a given period of time | 55 | |
| 1066266099 | Instantaneous rate | the slope of the tangent line to the curve of the concentration vs. time (also the first derivative) gives instantaneous rate, or the rate at a specific moment. | 56 | |
| 1066266100 | initial rate | the instantaneous rate at the moment the reactants are mixed | 57 | |
| 1066266101 | Equation: What is the equation that relates the reactant or product concentrations of the general equation: aA + bB → cC + dD | rate = -(1/a) (Δ[A] / Δt) = -(1/b) (Δ[B] / Δt) = (1/c) (Δ[C] / Δt) = (1/d) (Δ[D] / Δt) | 58 | |
| 1066266102 | What does the rate law express? | the rate as a function of reactant concentrations, product concentrations, and temperature. | 59 | |
| 1066266103 | Equation: rate law for the general equation: aA + bB → cC + dD | rate = k[A]^m[B]^n | 60 | |
| 1066266104 | What is the proportionality constant and what is important about it? | the rate constant, k. it is specific for a given reaction at a given temperature and does not change as the reaction proceeds. | 61 | |
| 1066266105 | reaction orders | the exponents of the rate law. define how the rate is affected by reactant concentrations. | 62 | |
| 1066266106 | rate law: if the rate doubles when [A] doubles, what is m? | m = 1 | 63 | |
| 1066266107 | rate law: if the rate quadruples when [A] doubles, what is m? | m=2 | 64 | |
| 1066266108 | T or F: reaction orders can be deduced from the reaction stoichiometry. | false, they must be found by experiment | 65 | |
| 1066266109 | What are the components of the rate law? | rate, reaction orders, and rate constant | 66 | |
| 1066266110 | How are the components of the rate law determined? | through experimentation | 67 | |
| 1066266111 | what is the general approach to determining the components of the rate law? | 1. use concentration measurements to find the initial rate. 2. use initial rates from several experiments to find the reaction orders. 3. use the determined values to calculate the rate constant. | 68 | |
| 1066266112 | what are three common approaches to measure the concentrations to find the initial rates? | spectroscopic methods, changes in pressures can be monitored, changes in conductivity can be monitored. | 69 | |
| 1066266113 | When is a reaction first order overall? | if the rate is directly proportional to a given concentration of a reactant | 70 | |
| 1066266114 | Equation: first order overall rate | Rate = k[A] | 71 | |
| 1066266115 | When is a reaction second order overall? | if the rate is directly proportional to the square of [A] | 72 | |
| 1066266116 | Equation: second order overall rate | Rate = k[A]² | 73 | |
| 1066266117 | When is a reaction zero order overall? | if the rate is not dependent on [A] at all | 74 | |
| 1066266118 | Equation: zero order overall rate | Rate = k[A]⁰= k | 75 | |
| 1066266119 | If given the rate law Rate = k[A][B] what are the orders? | first order with respect to A, first order with respect to B, second order overall | 76 | |
| 1066266120 | Reaction orders can/cannot be deduced from a balanced equation. | cannot | 77 | |
| 1066266121 | How do you find the reaction orders without a known rate law? | Run a series of experiments, each with a different set of reactant concentrations and obtain the initial rate in each case and take the ratio of their general rate laws | 78 | |
| 1066266122 | Equation: general equation of the ratio of rate laws | (Rate 2) / (Rate 1) = (k[A]₂^m[B]₂^n) / (k[A]₁^m[B]₁^n) | 79 | |
| 1066266123 | The rate constant is specific for a particular reaction at a particular ______. | temperature | 80 | |
| 1066266124 | What are integrated rate laws? | The integration of the a differential equation, that relates the rate of change in a concentration to the concentration itself, which relates the concentration to time. | 81 | |
| 1066266125 | What do integrated rate laws allow for? | the inclusion of time as a factor | 82 | |
| 1066266126 | T or F: The integrated rate law is unique for a particular reaction order. | true | 83 | |
| 1066266127 | Equation: integrated rate law for a first-order reaction | ln ([A]₀ / [A]) = kt | 84 | |
| 1066266128 | Formula: units of the rate constant for overall reaction orders | units of k = (L/mol)^(order - 1) / unti of t | 85 | |
| 1066266129 | Equation: integrated rate law for a second-order reaction | 1/[A] - 1/[A]₀ = kt | 86 | |
| 1066266130 | Equation: integrated rate law for a zero-order reaction | [A] - [ A]₀ = -kt | 87 | |
| 1066266131 | Equation: integrated rate law for a second-order reaction in slope intercept form | [A] = [ A]₀ - kt | 88 | |
| 1066266132 | Equation: integrated rate law for a first-order reaction in slope intercept form | ln [A] = ln [ A]₀ - kt | 89 | |
| 1066266133 | Equation: integrated rate law for a zero-order reaction in slope intercept form | 1/ [A] =1/ [ A]₀ + kt | 90 | |
| 1066266134 | If you obtain a straight line when you plot ln [reactant] vs time, the reaction is _____ to that reactant | first order | 91 | |
| 1066266135 | If you obtain a straight line when you plot 1/[reactant] vs time, the reaction is _____ to that reactant | second order | 92 | |
| 1066266136 | If you obtain a straight line when you plot [reactant] vs time, the reaction is _____ to that reactant | zero order | 93 | |
| 1066266137 | half-life of a reaction (t₁/₂) | the time required for the reactant concentration to reach half its initial value | 94 | |
| 1066266138 | the half-life of a _____ order reactant is a constant, independent of reactant concentrations | first-order | 95 | |
| 1066266139 | Equation: half-life for a first-order process | t₁/₂ = (ln 2 )/ k | 96 | |
| 1066266140 | The decomposition of each particle in a first-order process is independent of what? | the number of other particles present | 97 | |
| 1066266141 | Equation: half-life for a second-order process | t₁/₂ = 1/ (k[A]₀) | 98 | |
| 1066266142 | For a second-order process, the half-life is _____ proportional to the initial reactant concentration. | inversely. | 99 | |
| 1066266143 | as a second-order reaction proceeds, the half-life does what? | increases | 100 | |
| 1066266144 | Equation: half-life for a zero-order process | t₁/₂ = [A]₀/ 2k | 101 | |
| 1066266145 | the half-life of a zero-order reaction is ____ proportional to the initial reactant concentration | directly | 102 | |
| 1066266146 | Temperature affects the rate by affecting what? | the rate constant | 103 | |
| 1066266147 | Equation: Arrhenius equation | k = Ae ^ (-Ea/RT) | 104 | |
| 1066266148 | Activation energy, Ea | the minimum energy the molecules must have to react | 105 | |
| 1066266149 | As temperature increases, the rate constant _____. | increases | 106 | |
| 1066266150 | Equation: determining Ea if the rate constant of two temperatures is known | ln (k₂/k₁) = -(Ea/R)(1/T₂ - 1/T₁) | 107 | |
| 1066266151 | What does the collision theory view the reaction rate as? | the result of particles colliding with a certain frequency and minimum energy | 108 | |
| 1066266152 | What does the transition state theory offer? | offers a close-up view of how the energy of a collision converts reactant to product, insight into why activation energy is needed and how the activated molecules look | 109 | |
| 1066266153 | what is the basic tenet of collision theory | reactant particles must collide with each other to react | 110 | |
| 1066266154 | what does the collision theory explain? | why reactant concentrations are multiplied together in the rate law, how temperature affects the rate, and what influence molecular structure has on rate | 111 | |
| 1066266155 | how is collision theory is consistent with probability? | the observation that concentrations are multiplied in the rate law and hwy the rate depends on the product of the reactant concentrations instead of their sum | 112 | |
| 1066266156 | in terms of the collision theory, what does increasing the temperature of a reaction do? | it increases the average speed of the particles and therefore their collision frequency. | 113 | |
| 1066266157 | what is the energy threshold and why is it important? | Arrhenius proposed every reaction has an energy threshold that the colliding molecules must exceed in order to react, i.e. the Ea. Only the collisions with enough energy to exceed Ea can lead to reaction. | 114 | |
| 1066266158 | Activation energy, Ea | the energy required to activate the molecules into a state from which reactant bonds can change into product bonds | 115 | |
| 1066266159 | Temperature increase _____ the fraction of collisions with enough energy to exceed the activation energy | increases | 116 | |
| 1066266160 | Equation: the fraction of molecular collisions with energy greater than or equal to the activation energy | f = e^ -(Ea/RT) | 117 | |
| 1066266161 | The magnitudes of ___ and ___ affect the fraction of sufficiently energetic collisions | Ea and T | 118 | |
| 1066266162 | A reversible reaction has _____ activation energies | two: the Ea(fwd) and the Ea(rev) | 119 | |
| 1066266163 | the activation energy for the forward reaction, Ea(fwd) | the energy difference between the activated state and the reactants | 120 | |
| 1066266164 | the activation energy for the reverse reaction, Ea(rev) | the energy difference between the activated state and the products | 121 | |
| 1066266165 | the smaller the Ea or the higher the temperature, the ____ the value of k is and the _____ the reaction is | larger, faster | 122 | |
| 1066266166 | A larger Ea, or lower T, results in what? | a smaller k and a decreased rate of reaction | 123 | |
| 1066266167 | effective collisions | collisions that actually lead to product. the molecules must collide so that the reacting atoms make contact. | 124 | |
| 1066266168 | To be effective, a collision must have what? | enough energy and a particular molecular orientation | 125 | |
| 1066266169 | In the Arrhenius equation, the effect of molecular orientation is contained in what term? | the frequency factor, A | 126 | |
| 1066266170 | the frequency factor, A | the product of the collision frequency Z and an orientation probability factor, p, which is specific for each reaction and related to the structural complexity of the colliding particles. | 127 | |
| 1066266171 | Equation: the frequency factor | A = pZ | 128 | |
| 1066266172 | What does the transition state theory do? | details a hypothetical transition state that exists between reactants and products during a chemical reaction. The species formed in this hypothetical transition state is called the activated complex. The theory is used to explain how chemical reactions take place. Every reaction, and every step in an overall reaction, goes through its own transition state | 129 | |
| 1066266173 | another name for the transitional state | activated complex | 130 | |
| 1066266174 | what is the activated complex? | An extremely unstable species which is neither reactant nor product but a transitional species with partial bonds | 131 | |
| 1066266175 | The activation energy is the quantity needed to do what? | stretch and deform bonds in order to reach the transition state | 132 | |
| 1066266176 | reaction energy diagram | a diagram that depicts the transition state theory which shows the potential energy of the system during the reaction as a smooth curve. | 133 | |
| 1066266177 | Equation: Heat of reaction in terms of activation energy | ΔH(rxn) = Ea(fwd) - Ea(rev) | 134 | |
| 1066266178 | Most reactions occur through what? | A reaction mechanism | 135 | |
| 1066266179 | What is a reaction mechanism? | a sequence of single reaction steps that sum to the overall reaction | 136 | |
| 1066266180 | What is a reaction intermediate? | a substance that is formed and used up during the overall reaction | 137 | |
| 1066266181 | elementary steps or elementary reactions | the individual steps of the proposed reaction mechanism that describe a single molecular event and is not made up of simpler steps | 138 | |
| 1066266182 | An elementary step is characterized by its what? | molecularity | 139 | |
| 1066266183 | What is the elementary steps molecularity? | the number of reactant particles involved in the step | 140 | |
| 1066266184 | unimolecular reaction | an elementary step that involves the decomposition or rearrangement of a single particle | 141 | |
| 1066266185 | bimolecular reaction | an elementary step in which two particles react | 142 | |
| 1066266186 | termolecular reaction | an elementary step that involves the collision of three particles | 143 | |
| 1066266187 | why are termolecular steps extremely rare? | the probability of three particles colliding simultaneously with enough energy and with an effective orientation is very small | 144 | |
| 1066266188 | T or F: the rate law for an elementary reaction can be deduced from the reaction stoichiometry. | true | 145 | |
| 1066266189 | For an elementary reaction, its rate must be _____ to the product of the reactant concentrations because it occurs in _____ step(s). | proportional, one | 146 | |
| 1066266190 | The reaction order of an elementary reaction equals the what? | the molecularity | 147 | |
| 1066266191 | Equation: Rate law for a unimolecular elementary reaction A→product | Rate = k[A] | 148 | |
| 1066266192 | Equation: Rate law for a bimolecular elementary reaction: A+B→ product | Rate = k[A][B] | 149 | |
| 1066266193 | Equation: Rate law for a bimolecular elementary reaction: 2A → product | Rate = k[A]² | 150 | |
| 1066266194 | Equation: Rate law for a termolecular elementary reaction: 2A+B→product | Rate = k[A]²[B] | 151 | |
| 1066266195 | rate-determining step or rate-limiting step | the elementary step in a mechanism that is so much slower than the others that it limits how fast the overall reaction proceeds | 152 | |
| 1066266196 | T or F: The rate law of the rate-limiting step represents the rate law for the overall reaction. | true | 153 | |
| 1066266197 | What are the three criteria the proposed elementary steps for a mechanism must meet? | 1. The elementary steps must add up to the overall balanced equation. 2. The elementary steps must be physically reasonable (i.e. unimolecular or bimolecular). 3. The mechanism must correlate with the overall rate law. | 154 | |
| 1066266198 | The overall rate law includes only species active in the reaction up to/up to and including/after those in the rate-determining step. | up to and including | 155 | |
| 1066266199 | Each step in the mechanism has its own what? | transition state | 156 | |
| 1066266200 | If the rate-determining step is not the initial step it acts as a _____ and the past initial step _______ ________. | bottle neck, reaches equilibrium | 157 | |
| 1066266201 | An overall reaction rate law can include only _____ and _____ not _______. | reactants and products, not a reaction intermediate | 158 | |
| 1066266202 | what are the steps necessary to eliminate the reaction intermediate from the elementary rate law? | express the intermediate in terms of the reactant by setting the forward rate law of the fast, reversible step equal to the reverse rate law and solve for the intermediate, then substitute the expression for the intermediate into the rate law for the slow step. | 159 | |
| 1066266203 | What is a catalyst? | a substance that increases the rate without being consumed in the reaction | 160 | |
| 1066266204 | A catalyst causes a lower _____, which makes the rate constant ____ and the rate _____. | activation energy, larger, increase | 161 | |
| 1066266205 | T or F: A reaction with a catalyst yields more product than one without? | false | 162 | |
| 1066266206 | T or F: A reaction with a catalyst yields product more quickly than one without? | true | 163 | |
| 1066266207 | How does the catalyst cause a lower activation energy? | By providing a different mechanism for the reaction | 164 | |
| 1066266208 | A catalyst is not consumed, it is ______________. | used and regenerated | 165 | |
| 1066266209 | What are the two general categories of catalyst and what are they based on? | homogeneous and heterogeneous, whether the catalust occurs in the same phase as the reactant and product | 166 | |
| 1066266210 | homogeneous catalyst | exists in solution with the reaction mixture | 167 | |
| 1066266211 | heterogeneous catalyst | speeds up a reaction that occurs in a separate phase and is most often a solid interacting with gaseous or liquid reactants, usually having large surface areas. | 168 | |
| 1066266212 | T or F: Many reactions with a heterogeneous catalyst occur on a metal surface because the rate-determining step occurs on the surface itself. | true | 169 | |
| 1066266213 | The petroleum, plastics and food industry frequently used catalytic _______. | hydrogenation | 170 | |
| 1066266214 | What is catalytic hydrogenation? | a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. the reaction of the carbon-carbon double bond in alkenes with hydrogen in the presence of a metal catalyst. | 171 | |
| 1066266215 | enzyme | a protein whose complex three-dimensional shape, and thus its function, that catalyzes cell reactions. | 172 | |
| 1066266216 | every cell reaction has its own specific _______. | enzyme | 173 | |
| 1066266217 | every enzyme has a _____ that substrates bind to usually through intermolecular forces | active site | 174 | |
| 1066266218 | what is an active site | a small region whose shape results from those of the side chains, or R groups, of the amino acids that make it up | 175 | |
| 1066266219 | what are substrates | reactant molecules that bind to an active site on an enzyme which begins the chemical change | 176 | |
| 1066266220 | How do all enzymes function, regardless of their specific mode of action? | by binding to the reaction's transition state and thus stabilizing it. | 177 | |
| 1066266221 | enzymes ____ the activation energy which _____ the reaction rate | lower, increases | 178 |
