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CSU CHEM 113 - Exam 2 Study Guide

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Chem 113 1st EditionExam # 2 Study Guide Lectures: 9-17Lecture 9 (February 11)How are reaction orders determined?Reaction orders are determined from experimental data. NOTE: reaction orders are NOT determined by the balanced chemical equation.What is the relationship between reaction rates and reactant concentration? (Zero, First, and Second Order reactions)Zero-order reaction rates don’t change. First-order reaction rates increase linearly. In second-order reaction rates, the slope of the tangent lines of the curve increase gradually.What is the relationship between reactant concentration and time? (Zero, First, and Second Order reactions)Zero-order reaction rates decrease linearly. In first-order reaction rates, the slope of the tangentlines of the curve decrease gradually. In second-order reaction rates, the slop of the tangent lines of the curve decrease more rapidly than those in first-order reactions.Explain the effect of concentrations on reaction rates.In first-order reaction, the rate is proportional to the concentrations of the reactants. This is because the high the concentration, the more possibilities of collisions between molecules.Lecture 10 (February 13)What is an integrated rate law? Give examples of Zero, First, and Second order reactions.An integrate rate law takes time into account. In straight line form, the integrated rate laws for zero, first, and second order reactions are as follows: [ A ]t=−kt +[ A ]0, ln[A]t= -kt + ln[A]0, ,1[ A ]t=kt+1[ A]0.Describe a reaction half-life.A half-life of a reaction is the time it takes for the concentration of a reactant to drop to half of its initial value. It can be determined using the integrated rate law corresponding to the order ofthe reaction.Lecture 11 (February 16)What are the half-life relationships for zero, first, and second order reactions?For a zero order reaction, the half-life relationship is: t1 /2=[ A ]02 kFor a first order reaction, the half-life relationship is: t1 /2=ln 2kFor a second order reaction, the half-life relationship is: t1 /2=1k [ A ]0What is the collision theory? How is it affected by changes in concentration?The collision theory says that particles must collide a precise orientation in order to result in a reaction. Increasing the concentration results in an increase in the number of collisions betweenparticles, which therefore increases the chance of a speed of a reaction.How does temperature affect the rate constant (k)?As temperature increases, the value of k increases exponentially. This relationship is displayed inthe Arrhenius equation (k =A e−Ea/ RT) What is activation energy? What is the relationship between activation energy and the speed ofa reaction?Activation energy is the particular threshold that particles in a reaction must exceed in order to result in an effective reaction. It is the energy difference between the reactants and the activated state of the particles. As the activation energy decrease, the speed of the reaction increases.What is the transition state theory?A transition state is formed by an effective collision between particles; it’s an unstable species containing partial bonds. The transition state exist at the point of maximum energy potential. The energy required to form the transition state is the activation energy.Zero Order First Order Second OrderRate Law Rate=k Rate=k[A] Rate=k[A]2Units for k mol/L*s 1/s L/mol*sHalf-life[ A ]02 kln 2k1k [ A ]0Integrated Rate Law in straight-line form[ A ]t=−kt +[ A ]0ln [ A ]t=−kt +ln [ A]01[ A ]t=kt +1[ A]0Plot for straight line [A]t vs. t ln[A]t vs. t1[ A ]t vs.tSlope, y-intercept -k, [A]0-k, ln[A]0k, 1[ A ]0Lecture 12 (February 18)What is a multi-step reaction? Can net reaction have different sets of intermediary reactions?A multi-step reaction has more than one step, or mechanism. Net reactions can have different sets of intermediary reactions as long as they have the same results.What are the three different types of molecularity a reaction mechanism can have?Reaction mechanisms can be unimolecular, bimolecular, or termolecular. These molecularities depend on how many reactant molecules there are in a reaction mechanism.How can rate laws of elementary steps be determined?The rate law of an elementary reaction can be determined by the stoichiometry of the balanced chemical equation.How are the rate laws of reactions with several mechanisms determined?The slow mechanism determines the relevance of the rate steps and the overall rate law. To check the total rate law, all of the steps through the slow step are considered.Lecture 13 (February 20)What is a rate-determining step?A rate-determining step, or a rate-limiting step, is the slowest step in the reaction. The rate law for the rate-determining step becomes the rate law for the overall reaction.Lecture 14 (February 23)What are the relative probabilities of molecularities of a reaction?Termolecular reactions are highly unlikely to occur, while unimolecular and bimolecular reactionare much more likely to occur.What is the effect of a catalyst on a reaction? What factors of a reaction does a catalyst not effect?A catalyst lowers the total activation energy of the forward and reverse reaction, speeding themboth up. It is not consumed during a reaction. The use of a catalyst in a reaction does not affect the change in Gibbs free energy, the change in Enthalpy, or the equilibrium position.What is the difference between homogeneous catalysis and heterogeneous catalysis?Homogeneous catalysis is when the catalyst is in the same phase as the reactant. Heterogeneous catalysis is when the catalyst is in a different phase from the reactants.Lecture 15 (February 25)What is chemical equilibrium?Chemical equilibrium occurs when reactions are reversible; it is the state where the concentrations of reactants and products are constant and the rates of the forward and reverse reactions are equal.What is the equilibrium constant (K)? What does it indicate?K is the ratio of rate constants from individual reaction rates. It reflects a ratio of product concentrations to reactant concentrations for a reaction. It indicates how far the reaction proceeds towards the products at a given temperature.What does a small value of K indicate? What does a large value of K indicate?A small value of K indicates that the reaction yields little product before reaching equilibrium and the reaction favors the reactants. A large value of K indicates that the reaction reaches equilibrium


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