Chemistry 1024A/B Lecture Notes - Lecture 5: Exponential Decay, Reaction Rate Constant, Reaction Rate

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6 Apr 2016

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Reaction rate: is a measure of how fast a reactant is used up or how fast a product is formed in a chemical reaction. We (cid:449)ill ofte(cid:374) use (cid:862)(cid:272)o(cid:374)(cid:272)e(cid:374)tratio(cid:374)s(cid:863) (cid:894)(cid:373)ol/l(cid:895) for substances in solution and for gasses. One problem arises, for a ->b (cid:449)e (cid:272)ould also (cid:271)ase the defi(cid:374)itio(cid:374) of (cid:862)rate(cid:863) o(cid:374) the (cid:272)ha(cid:374)ge of [a]. This would result in a negative rate, whereas the increase of [b] would result in a positive rate. A minus sign added for the reactants. In general form rate is defined as, for the balanced equation is; If a plot of concentration vs. time is available, the rate can be determined from the slope of the plot. Pe(cid:272)ies have to (cid:862)(cid:373)eet(cid:863) (cid:894)(cid:272)ollide(cid:895) (cid:271)efore they (cid:272)a(cid:374) rea(cid:272)t with each other. The probability to collide with other molecules is high, if these other species have a high concentration.

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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

113. In this chapter we have seen a number of reactions in which a single reactant forms products. For example, consider the fol lowing first-order reaction: CH3NC(g) -CH,CN(g) However, we also learned that gas-phase reactions occur through collisions. a. One possible explanation for how this reaction occurs is that two molecules of CH3NC collide with each other and form two molecules of the product in a single elementary step. If that were the case, what reaction order would you expect? b. Another possibility is that the reaction occurs through more than one step. For example, a possible mechanism involves one step in which the two CH3NC molecules collide, result- ing in the "activation" of one of them. In a second step, the activated molecule goes on to form the product. Write down this mechanism and determine which step must be rate determining in order for the kinetics of the reaction to be first order. Show explicitly how the mechanism predicts first order kinetics.

Help with b-e would be appreciated - I'd like to check my answers before turning in. TY!

Genetically engineered streams of Essen eruvim colt have become essential tools in the production of recombinant human peptides and proteins. One of the first sub- the synthesized using engineered E coli was recombinant human insulin or humbling, for the treatment of people suffering from type I diabetes mellitus. A simple fiction scheme for the production of humbling is described below. Bacteria consume glucose under aerobe conditions, and produce humbling and biomass C_6 H_12 O_6 (glucose) + O_2 + NH_3 (ammonia) rightarrow C_2.3 H_2.8 O_1.8 N (humulene) + CH_1.9 O_0.3 N_0.3 (biomass) + CO_2 + H_2O A typical humbling production scheme consists of k. coli cultured in a large bioreactor. A continuous stream of media is fed into the reactor. A continuous products and unused reactants is removed from the bioreactor for further processing, including purification of the humbling for therapeutic use. Media containing glucose and ammonia is fed into the reactor at a rate of 100 L/hr; the concentrations of glucose and ammonia in that stream are 150 mM and 50 mM, respectively. Pure oxygen gas is sparked (i.e., bubbled) into the reactor at a rate of 100 mL/min. The exit flow rate of liquid containing biomass, product, and excess reactant is 100 I7hr. Assume that there is no it coagulation in the system. Assume that the reaction goes to completion. Write element balances for C, H, O, and N. Write two additional balance equations given the following information: The ratio of humbling to biomass production is 1:5. Solve for the stoichiometric coefficients to balance the equation. Determine the inlet molar flow rates of glucose, oxygen, and ammonia in mol/hr. In this bioreactor, temperature is V10 K and pressure is 1 atm. Determine the limiting reactant, the reaction rate tR), and the fractional conversion of glucose, Calculate the molar flow rates of all constituents leaving the bioreactor. The it sired output of the bioreactor is 1 kg/day of humbling. Can this output be achieved by increasing the oxygen flow rate.' Justify. Acetic acid (vinegar) can be produced via the reaction:

Chemistry 1024A/B Lecture Notes - Lecture 5: Exponential Decay, Reaction Rate Constant, Reaction Rate

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