1. Collision Theory 2. Activation Energy 3. Potential Energy Diagrams

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1 Chemistry 12 Reactio Kietics II Name: Date: Block: 1. Collisio Theory 2. Activatio Eergy 3. Potetial Eergy Diagrams Collisio Theory (Kietic Molecular Theory) I order for two molecules to react, they must with each other. Whe they collide they trasfer amog themselves. Cosider a hypothetical reactio betwee two gas particles, A ad B, to form AB accordig to the reactio: A (g) + B (g) à AB (g) Total possible collisios: The rate of reactio is directly proportioal to the product of the cocetratios of the reactats. Whe two variables are directly proportioal to oe aother, there is a costat that relates the two, called a proportioality costat, represeted by the letter k. Rate Law: Reactio rate = The proportioality costat is called a rate-costat. Each reactio has its ow uique rate law ad its ow uique rate costat. For may reactios, x ad y are equal to 1, ad are called reactat orders. We will oly be dealig with reactios with a order of Assume a reactio occurs by this rate law: rate = k[a]. How would the rate be affected by each of the followig chages i cocetratio? a) [A] is doubled. b) [A] is halved. 2. Assume a gaseous reactio occurs by this rate law: rate = k[a][b]. How would the rate be affected if the volume of the cotaier were halved?

2 3. We also kow that temperature chages the rate. a) Cosiderig the rate law, rate = k[a], how is the rate of a reactio affected by icreasig temperature? b) What part of the rate law must be affected by chagig temperature? Most collisios are ot successful ad do ot result i a reactio. A successful collisio requires the followig: Which of the followig reactio is fastest? a. H 2(g) + I 2(g) à 2HI (g) b. Ag + (aq) + I - (aq) à AgI (s) c. C 6H 12O 6 (s) + 6 O 2(g) à 6 CO 2(g) + 6 H 2O (g) d. 5C 2O 4 2- (aq) + 2MO 4 2- (aq) + 16H + (aq) à 10CO 2(g) + 2M 2+ (aq) + 8H 2O (l) Activatio Eergy (E a) Activatio Eergy: Must overcome: o Repulsive forces betwee electro clouds of the reactig molecules o Weake or break bods

3 Trasitio State Theory: Whe molecules have eough kietic eergy to react collide, their electro clouds iitially repel oe aother to form a ustable trasitory cofiguratio of atoms. Because they have sufficiet kietic eergy to overcome this, the ustable complex will form the desired products. Bod breakig requires eergy, while bod formig results i eergy. Example: H 2 (g) + I 2 (g) à 2 HI (g) Potetial Eergy Diagrams Potetial Eergy Diagrams: Graphical represetatio of the eergy chages that take place durig a chemical reactio. The activatio eergy, Ea, is the differece betwee the potetial eergy of the activated complex ad the potetial eergy of the reactat molecules. It represets the amout of eergy the reactat molecules must gai to form a activated complex. E a = The ethalpy chage (ΔH) is the differece betwee the total potetial eergy of the products ad the total potetial eergy of the reactats. ΔH = Calorimetry the sciece of measurig the chage i heat associated with a chemical reactio

4 1. Label each arrow i the followig diagram: Progress of Reactio 2. Cosider the followig graph o the right. a) What is the potetial eergy of the activated complex? b) What is the activatio eergy of the reactio? c) What is the ΔH for this reactio? d) Is the reactio edothermic or exothermic? POTENTIAL ENERGY Progress of Reactio ReactioReactio May chemical reactios are reversible uder certai coditios. The first potetial eergy diagram could be read i reverse to give the same measuremets provided by the secod diagram.

5 3. Aswer the followig questios about this potetial eergy diagram: a) Give ΔH for the forward reactio. Is this reactio exothermic or edothermic? b) Give ΔH for the reverse reactio. Is this reactio exothermic or edothermic? c) Give E a for the forward reactio. d) Give E a for the reverse reactio. e) Which is faster, the forward or reverse rate? f) Give the potetial eergy for the activated complex. How does this value compare for the forward ad reverse reactios? 4. Cosider the graph ad equatio o the right: a) What species represets the trasitio state? b) Which is faster, the forward or reverse rate? c) Circle the specie(s) that has the strogest bods: A 2 + B 2 OR AB d) Explai your aswer to the questio above. Hebde Workbook: Pg. 23 #34, 37 Pg. 25 #41-45

In order for two molecules to react, they must with each other. When they collide they transfer among themselves.

Chemistry 12 Reaction Kinetics II Name: Date: Block: 1. Collision Theory 2. Activation Energy 3. Potential Energy Diagrams Collision Theory (Kinetic Molecular Theory) In order for two molecules to react,