CHM 1311 Lecture 6: Chemistry Lecture #6

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blackgoldfish265

3 Nov 2016

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The concentration of reagent and products does not change. Dynamic chemical equilibrium (the k i have drawn is a small k, but i used big, because the d and p need to look small compared to it) The formation of dinitrogen tetroxide from nitrogen dioxide: We can consider this reaction a dynamic" equilibrium: The rates of the forward and reverse chemical reactions are equal. How can we visualize a dynamic" equilibrium? kp = rate of product formation. The rate of the forward and reverse chemical reactions are equal at equilibrium. Rate product formation = (rate constant) x [reagent(s) req. for product]^stoich. coef cient. How to express the rate of a dynamic chemical equilibrium: Dynamic chemical equilibrium can be characterized by the elementary components in the reaction: At equilibrium, we know that kp = kd. If we know that the rate of the forward (production formation) reaction is equal to the rate of the reverse (product decomposition) reaction, then:

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ENT ives To determine equilibrium concentrations for species in solution . Examine temperature effects on reaction equilibrium Investigate the shift in equilibrium from different stresses on a system kills . Use colorimeter to determine unknown solution concentrations ced .Preparing temperature baths to change reaction conditions tionEquilibrium is defined as a state in which the concentrations of both the reactants and products have no tendency to change with time. We can restate this by saying that the rate of the forward reaction is equal to the rate of the reverse reaction. Recall that with rate we are simply defining how fast a reaction is proceeding, a speed at which the reaction proceeds. Take note that when writing an equilibrium expression, pure liquids (denoted by l or 2) and pure solids (denoted by s) are omitted. Typically we express the equilibrium by K or Kp where c and p denote either concentration or partial pressure respectively. We refer to this value of K, or Kp as an equilibrium constant For any reaction, Kc can be written as the product of the concentration of products, raised to their stoichiometric coefficients, divided by the product of the concentration of the reactants raised to their stoichiometric coefficients. See Equation (5-1) below for an example: aA(aq) + bB(aq-cC(aq) + dD(aq) (5-1) A] [B]b As mentioned before, K, or K, are equilibrium constants meaning that they will have the same value unless temperature is changed. This brings in two important ideas 1) We can perturb the equilibrium concentrations of a reaction, say [A] for instance which will cause the other concentrations to shift so that K for the reaction remains constant. 2) If we change temperature, we will either increase or decrease our value of K depending on the specific reaction we are examining. Determining K, and Equilibrium Concentrations During lecture we often discuss the idea of using ICE tables as a method for organizing and calculating concentrations of reactions as they proceed towards equilibrium. In a typical ICE table you need to know initial concentrations and the magnitude of K to determine the equilibrium concentrations. Alternatively, if you know the equilibrium concentrations for a reaction you can calculate K. For this experiment we will be examining a complex ion formation, when iron(III) ion

to the left is a picture of what the right side should look like. I asked for explanations from my prof and ended up more confused! Can someone help me please?

c wve established the equilibrium, manipulate the concentrations in brium first to the right and then to the left. Record your observations, veri the change in reaction rate (for the forward or reverse reaction) after e the equilibrium. hexaaquacobalt(I) i ink chloride ion colorless tetrachlorocobaltate( blue Use small test tubes and minimal amounts of solutions; usually a fi agents: 0.1A, Coch, 2MHCL 0.1MAgNo, re.(CoC14.) Equilibrium expression: Hexaaquacobalt(II) ion. [Co(H2O)J is produced by: C o CI 2ã he net ionic equation is: ( 0ã+ t G, H20-7 [() ( t1 he equilibrium will be shifted to the RIGHT by (Choose a reagent to ad ce. Do not add more reagent than the minimum amount needed to change concentration of a reagent becomes too great, you may not be able to shi again, or, unexpected side reactions may occur. If you keep your solut able to shift the equilibrium back and forth with relative ease. 1. Reagents: 0.1 MK,Cr, MHC, MNaOH Cr,072-(aq) ä¸ H2Oã® 2CrO4 2 + HCI servation that suggests the equilibrium is shifted to the right: (Color perature change, precipitate formation) CoNeY a. Dichromate ion produced by Cr2t Â·Hz b. Equilibrium shifted to the right by NaO c. Observation color change oro d. Net Ionic Equation net ionic equation is reason for the shift: (Forward or reverse reaction speeds up or slows. Reason for shift quilibrium will be shifted to the LEFT by: (Choose a reagent to ad (o uare f. Equilibrium shifted to the lefi by s. Observation cord h. Net lonic Equation 26 ation that suggests the equilibrium is shifted to the left: (Color Reason for shift Reagents: 0.1 M BaCI, 0IMNHC,04 verse ha pre ature change, precipitate formation) ãUY ionic equation is: son for the shift: (Forward or reverse reaction speeds up or slow g the temperature will shift the equilibrium in which direction? ion that suggests the equilibrium is shifting: (Color change, gas white a. Barium oxalate produced by b.Net lonic Equation Equilibrium shifted to the right by d. rvation ipitate formation)color narki k e. N shift: (Forward or reverse reaction speeds up or slov uilibrium shifted to the left by tion exothermic or endothermic? h. nic equation is: c Equation Reason for shift

For a reaction aA rightarrow Products, [A]_o = 13 M, and the first two half-lives are 35 and 70 minutes, respectively, a) Write the rate law for this reaction. b) Calculate k. c) Calculate [A] at t = 335 minutes The Model of Chemical Kinetics represents the reaction rate constant as: k = (2p) times exp(-Ea/RT). What does each variable in the equation mean- that is, in regard to their contribution towards the reaction rate constant? In other words, what does each variable actually mean/refer to? Chemists commonly use a rule of thumb that an increase of 10 K in temperature doubles the rate of a reaction. What must the activation energy be for this statement to be true for a temperature increase from 63 degree C to 73 degree C? ln(k_2/k_1) = E_a/R(1/T_1 - 1/T_2) (i) What is a catalyst? (ii) What are the two types of catalysts? Explain specifically why they are different? (iii) What is one example of each type of catalyst? (i) What does it mean when a reaction is in chemical equilibrium? Specifically, within the context of reactants? products, and the forward and reverse reaction rates, what does chemical equilibrium mean? (ii) What is Le Chateleir's Principle? Within the context of reactant/product concentration, temperature, and pressure, how does Le Chatelier's Principle predict a reaction will respond to variations in reactant, product concentration, temperature, and pressure. (i) For the given reactions: N_2(g) + 3H_2(g) harr 2NH_3(g), H_2O(g) + CO(g) harr H_2(g) + CO_2(g), HCN(aq) harr H^+(aq) + CN^-(aq), 2KClO3(s) harr 2KCl(s) + 3O_2(g) and 2H_2 O(l) harr 2H_2(g) + O_2(g). Write the equation that governs each of their equilibrium rate constant K (ii) If N_2(g) + 3H_2(g) harr 2NH_3(g)'s (at 25 degree C) has K = 25, what would K be (at 25 degree C) for 2NH_3(g) harr N_2(g) + 3H_2(g)? (iii) What would K be if [5 times (N_2(g)+3H_2(g) harr 2NH_3(g)]? (i) For N_2(g) + 3H_2(g) harr 2NH_3(g): P_NH3: 1.9 times 10^-1 atm, P_N2 = 8.9 times 10^-2 atm, P_H2 = 1.9 times 10^-2 atm, what is K_p? (ii) Using K_p, calculated in the previous step, what is K at 45 degree C, where K_p = K(RT)^Delta n? (R = 0.08206 L atm/mol K). What is the difference between homogeneous and heterogeneous? (ii) If K is larger than 1, does the equilibrium life farther to the right (favoring the production of products) or to the left (favoring reactant formation)? (iii) If K is less than 1, does the equilibrium life farther to the right (favoring the production of products) or to the left (favoring the production of reactants)?

CHM 1311 Lecture 6: Chemistry Lecture #6

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