Reaction Rate Measure of the rate of disappearance of one of the reactants or appearance of one of the products Measured as Molarity/time (M/s)

What has to happen for the reaction to take place? Reactants have to meet Reactants have to be positioned correctly Reactants have to have sufficient energy to produce product Concentration, temperature, How does concentration and temperature impact reaction rate?

Reaction Profile What is the effect of a catalyst? Energy Time Activated Complex – Transitional structure Is reaction endothermic or exothermic? What is the effect of a catalyst? Activation Energy Energy Reactants Catalyst allow for a different mechanism(way) for the reaction to take place Products Time

What will happen to the concentration of reactant A versus time? Rxn: A -> Products Rate = change in conc change in time What will happen to the concentration of reactant A versus time? Slope of the line represents rate Reaction rate varies Initially faster, then slows down… why???

Rate Law… what is it? How do I find it? Mathematical expression of Reaction rate as a function of reactant concentration Experimentally determined Can use the “Method of Initial Rates” to find the initial rate  Some reactants impact reaction rate more than others, some actually may not impact reaction rate at all.

Method of Initial Rates Rxn: A + 2 B -> 2 C Rate Law: Rate = k[A]x[B]y Exp Initial [A] Initial [B] Initial Rate 1 0.100 M 2.73 M/s 2 0.150 M 6.14 M/s 3 0.200 M 5.42 M/s k is the rate law constant What is factored into the constant? Constant factors in activiation energy, steric considerations, temp Trials are run, data is collected An example of a zero-order reaction might be an electrode reaction in which only the material adsorbed on the surface of the electrode can react. If the reactant is strongly adsorbed from the solution but can adsorb only to the extent of a single layer of molecules, the surface may be completely and uniformly covered by that layer at any realistic concentration in the electrolyte solution. The surface concentration of the reactant, which is the only concentration of the reactant directly involved in the reaction, will then remain constant even though the electrolyte concentration varies over orders of magnitude. Zero-order rate laws can also arise as a result of several successive steps in more complex reaction mechanisms.

Do Now – In your own words, what is the rate law? How does it capture all the factors that impact reaction rate? Monday we used the method of initial rates. What happens initially that allows us to calculate the rate law? How do you find the rate law? Exp Initial [A] Initial [B] Initial Rate 1 0.100 M 2.73 M/s 2 0.150 M 6.14 M/s 3 0.200 M 5.42 M/s

The rate law for the reaction of A + 2B -> C is rate = 2730/M2s[A]o2[B]o What is the order of A? B? the overall order? Which reactant has a greater effect on the reaction rate? What happens to the rate if the concentration of A is doubled? If the concentration of B is doubled? If the concentration of A is tripled? What is the rate if [A]o= .0500 M and [B]o = .0256 M (oh and what do the little circles mean?

Do Now What is reaction rate? What does the term “equilibrium” signify? Can you describe physical changes in the chemistry lab where equilibrium is achieved? When calculating the mass of product produced using stoichiometry, what assumption do you make about the amount of reactant you started with? What is meant by chemical equilibrium? Which components of the reaction (reactants/products) are present at this point? What happens to the concentrations of those species once equilibrium is established?

MB + electrons -> MB- (yellowish) Methylene Blue, (MB) reacts with basic, sugar solution, and is reduced (gains electrons) MB + electrons -> MB- (yellowish) Shaking, dissolves oxygen into solution, and oxidizes (removes electrons) from MB- MB- -> MB + electrons (blue) In this reaction, glucose (an aldehyde) in an alkaline solution is slowly oxidized by dioxygen to form gluconic acid: CH2OH–CHOH–CHOH–CHOH–CHOH–CHO + 1/2 O2 --> CH2OH–CHOH–CHOH–CHOH–CHOH–COOH Gluconic acid is converted to sodium gluconate in the presence of sodium hydroxide. Methylene blue speeds up this reaction by acting as an oxygen transfer agent. By oxidizing glucose, methylene blue is itself reduced (forming leucomethylene blue), and becomes colorless. If there is a sufficient available oxygen (from air), leucomethylene blue is re-oxidized and the blue color of solution can be restored. Upon standing, glucose reduces the methylene blue dye and the color of the solution disappears. In dilute solutions the reaction takes place at 40-60°C, or at room temperature (described here) for more concentrated solutions.

What is dynamic equilibrium? Chemical Equilibrium Two opposing chemicals reactions occur at the same rate: H2(g) + I2(g) <-> 2HI(g) Forward: H2(g) + I2(g) -> 2HI(g) Do blue bottle demo – some rxn reversilbe. In theory all are, however some are reversible on own, others under specific conditions, , others nevers. Reverse: 2HI(g) -> H2(g) + I2(g)

Do demo

Will we able to use stoichiometry to predict amount of materials that will be produced? No! Nothing is consumed. Everything will be present!!! We will need another means to solve.

N2(g) + 3H2(g) <-> 2NH3(g) N2 H2 NH3 Exp1: Initially 1.0 M 1.0 M 0 Exp 2: Initially 0 0 1.0 M Exp 3: Initially 2.0 M 1.0 M 3.0M Nothing is consumed!!! At equilibrium 0.921M 0.763M 0.157M At equilibrium 0.399M 1.197M 0.203M At equilibrium 2.59M 2.77M 1.82M after accumulating a lot of data is was discovered that ratio of conc of prod/react is a constant called law of mass action - active mass was an early term for concentration

Law of Mass Action The ratio of product concentrations to reactant concentrations at equilibrium is constant. For reaction aA + bB <-> cC + dD Equilibrium Expression is K = [C]c[D]d [A]a[B]b It was found in mid 1800’s, proposed law (Guldberg and Waage) Always constant at a given temp regardless of how rxn starts. All rxn process to an eq state where ratio is the same. Can use this to calculate. Only solution or gas concentration entered into expression. Solid and liqiud “conc” does not change. As long as some is present reaction continue, values factored into K as they are constnat Equilibrium Constant

Do Now What is K

Do Now: 1. Write balanced chemical reactions and equilibrium expressions for: Hydrogen and oxygen gases reversibly produce water vapor Tetratomic solid phosphorus reacts reversibly with gaseous nitrogen monoxide to produce solid P4O6 and nitrogen gas Solid carbon reacts with carbon dioxide gas to reversibly produce carbon monoxide gas 2. What is K? What factors will affect K? Where does it come from?

The equilibrium constant, K for the reaction H2(g)+F2(g)<->2HF(g) has the value of 2100 at a particular temperature. When the system is analyzed at equilibrium at this temperature , the concentrations of H2 and F2 are both found to be 0.0021 M. What is the concentration of HF in the equilibrium system under these conditions?

What does the size of K indicate Extent to which a reaction proceeds to completion 2O3 <-> 3O2 K=1 x 1055 2HF <-> H2 + F2 K=1 x 10-13 N2 +3H2 <-> 2NH3 K=10 Large – equil.ibrum lies to right Small – eq lies to left Depends on energetic of rxn, not timing ( on change is energy, DH)

1. 00 moles of dinitrogen trioxide is placed into a 2 1.00 moles of dinitrogen trioxide is placed into a 2.0 L flask at 25ºC and 1 atm and it decomposes into nitrogen dioxide and nitrogen monoxide reversibly. Write an equation to describe this reversible gas phase reaction What is the composition of the reaction mixture at equilibrium if it contains 0.30 moles of nitrogen dioxide? What is the value of the equilibrium constant, K?’ You placed 1.00 mole dinitrogen trioxide into a 2.0 L flask at 25C and 1 atm and it decomposes into nitrogen dioxide and nitrogen monoxide. What is the composition of the reaction mixture at eq if it contains 0.30 mole nitrogen dioxide. Also what is K

Do Now What is the law of mass action? What do we use it for? What is an ICE table? What is it’s purpose?

The formation of hydrogen fluoride from hydrogen and fluorine has an equilibrium constant of 115 at a certain temperature. Write a reversible reaction and an equilibrium expression. In a particular experiment 3.00 moles of each component is added to a 1.50 L flask. Calculate the equilibrium concentrations of all species.

Do Now Have new HW ready. Take a look at the old HW. I will go over any problems (from either HW) that you would like. If you are good, work on the next HW set.

Do Now: What is an ice table used for? How do we know if we need it? What is the quadratic equation? When do we have to use it?

For the reaction: 2NO(g)<->N2(g)+O2(g) the equilibrium constant is 2400 at a certain temperature. For which of the following sets of conditions is the system at equilibrium? For those that are not at equilibrium, in which direction is the reaction proceeding toward equilibrium. A) 1.0 L flask contains 0.24 mole NO, 2.0 mol N2, and 2.6 mole O2 B) 2.0 L flask contains 0.032 mole NO, 0.60 mol N2, and 4.1 mole O2 C) 1.0 L flask contains 0.060 mole NO, 4.4 mol N2, and 3.7 mole O2

Reaction quotient, Q A tool used to determine if a reaction is at equilibrium Insert any concentrations you have and find the quotient, Q Compare to the K, the equilibrium constant.

What is Le Châtelier’s Principle? If a stress is applied to an equilibrium system, the reaction will shift in a direction that tends to reduce the change. Factor control the position of a chemical equilibrium. Chemists and chemical engineers will choose conditions that will favor the production of the desired product as much as possible. Fritz Haber develop the process of the synthesis of ammonia from n2 and h2 he modified temp and pressure to maximized production of ammonia

N2(g) + 3H2(g) <-> 2NH3 DH =-92 kJ Stress Shift [N2] [H2] [NH3] Add N2 Remove NH3 Increase Temperature Increase Pressure(by decreasing V) Add catalyst Increase Volume Add acid (NH3 is a base) Reaction at equilibrium

Do Now Bring me your HW when I call you. Work on review problems. Prepare any questions you have. Test is on Friday. Get prepared. Some of you were very unprepared last time based on your responses to the multiple choice and problems which were very similar if not identical to the problems we did in class/HW!!!

Do Now: Describe LeChatelier’s principle in your own words. Looking at the boxed table of equations in your lab… 2. What types of equations are presented in the table? 3. In Part A: If solutions of FeCl3(aq) and KSCN(aq) were added to a container, which ions would they provide in reference to the equation in the table. 4. If the reaction had already reached equilibrium, and more FeCl3 was added, what would happen? Apply LeChatelier’s principle and write it out… in sentence(s) in proper English!!! 5. In Part B: If solutions of K2CrO4(aq) or K2Cr2O7(aq) were added… what would they provide in terms of the equation in the table? 6. What type of substances are HCl and NaOH?

Do Now In your own words, describe LeChatelier’s principle. What are the two reaction systems we will investigate today? From your experience, describe what you know about a solution of HCl. From your experience, describe what you know about a solution of NaOH. What is H3O+? When is it present in large amounts?

Do Now: Take out Hw and lab. Have answers highlighted. Bring them to me FOUR students at a time. If you are not at my desk, please read the lab for tomorrow (left on your desk) or work on the additional worksheets I left for you or that I gave you on Monday. Also prepare questions for our review which may include going over any HW problem or topic.

What is stability??? Thermodynamically stable - the reaction will not take place spontaneously, overall energy change for the reaction is positive Kinetically stable – the reaction will take place spontaneously, however the reaction proceeds so slowly we can not detect a change

Do Now Highlight, IN COLOR, the answers… 31. mol H2 33. concs. at eq 53. init and eq conc of HI 81. K 21. Pressure changes and why 69. “at eq” or direction rxn proceeds Then, bring up to me no more than 3 students at a time. Work on next HW!

Check answers 15.31 (.173 mol) 15.33 ( [H2]=[Br2]= 0.00018M; [HBr] = 0.267M) 15.53 ([HI] Initial= 0.35M; Eq = 0.53 M) 15.81 (1.7) 21. PCl3 and Cl2 increase, PCl5 decreases because Q<K 69. a. eq b. proceeds right c. proceeds left

15.39 , 41 15.45( a. increases, b. decreases, c. no change) 15.49

Do Now … Mark up your HW, in color, as follows… The practice exercise problem – highlight the direction reaction proceeds 45 – highlight increase/decrease/no change in your response 69 – highlight if at eq or direction reaction proceeds 21 – highlight what will happen to PCl3, PCl5, and Cl2 After you have your HW checked you may do one part of 49 on the board for a mole$

Given the reaction, 2NH3(g)<-> N2(g)+ 3H2(g) Write the equilibrium expression The following equilibrium concentrations were observed at 127ºC [NH3]= 0.031 M [N2] = 0.85 M [H2] =0.0031 M Find the value of the equilibrium constant

Do Now What is the law of mass action? How do you write an equilibrium expression and what is it used for? Consider the following equilibrium process: 2NO2(g) <-> 2NO(g) + O2(g) Kc = 1.58 at 1000 K. The equilibirum concentrations of oxygen and nitrogen dioxide are 0.25 M and 0.36 M, respectively. Determine the equilibrium concentration of nitrogen monoxide.