Chem 211 1st EditionExam # 2 Study Guide I. Factors That Influence Reaction RateA. Particles must collide in order to react.B. The higher the concentration of reactants; the greater the reaction rate.C. A higher concentration of reactant particles allows a greater number of collisions.D. The physical state of the reactants influences reaction rate.E. Substances must mix in order for particles to collide.F. The higher the temperature, the greater the reaction rate.G. At higher temperatures particles have more energy and therefore collide more often andmore effectively.H. Sufficient collision energy is required for a reaction to occur.II. Expressing the Reaction RateA. Reaction rate is measured in terms of the changes in concentrations of reactants or products per unit time.B. For the general reaction A → B, we measure the concentration of A at t1 and at t2:C. Square brackets indicate a concentration in moles per literD. The negative sign is used because the concentration of A is decreasing. This gives the rate a positive value.III. The Rate LawA. For any general reaction occurring at a fixed temperatureB. aA + bB → cC + dDC. The term k is the rate constant, which is specific for a given reaction at a given temperature.D. The exponents m and n are reaction orders and are determined by experiment.E. The values of m and n are not necessarily related in any way to the coefficients a and b.IV. Reaction OrdersA. A reaction has an individual order “with respect to” or “in” each reactant.B. For the simple reaction A → productsC. If the rate doubles when [A] doubles, the rate depends on [A]1 and the reaction is first order with respect to A.D. If the rate quadruples when [A] doubles, the rate depends on [A]2 and the reaction is second order with respect to [A].E. If the rate does not change when [A] doubles, the rate does not depend on [A], and the reaction is zero order with respect to A.V. Individual and Overall Reaction OrdersA. For the reaction 2NO(g) + 2H2(g) → N2(g) + 2H2O(g):B. The rate law is rate = k[NO]2[H2]C. The reaction is second order with respect to NO, first order with respect to H2 and third order overall.D. Note that the reaction is first order with respect to H2 even though the coefficient for H2in the balanced equation is 2.E. Reaction orders must be determined from experimental data and cannot be deduced from the balanced equation.VI. Determining Reaction OrdersA. For the general reaction A + 2B → C + D, the rate law will have the formB. Rate = k[A]m[B]nC. To determine the values of m and n, we run a series of experiments in which one reactant concentration changes while the other is kept constant, and we measure the effect on the initial rate in each case.D. We inspect the exponents in the rate law, not the coefficients of the balanced equation, to find the individual orders. We add the individual orders to get the overall reaction order.E. Sometimes the exponent is not easy to find by inspection. In those cases, we solve for m with an equation of the form a = bm:F. This confirms that the reaction is first order with respect to O2G. Reaction orders may be positive integers, zero, negative integers, or fractions.H. The value of k is easily determined from experimental rate data. The units of k depend on the overall reaction order.VII. Determine the kinetic parameters of a reactionA. Determine slope of tangent at t0 for each plot.B. Compare initial rates when [A] changes and [B] is held constant (and vice versa).C. Substitute initial rates, orders, and concentrations into rate = k[A]m[B]n, and solve for k.VIII. Integrated Rate LawsA. An integrated rate law includes time as a variable.B. First-order rate equationC. A plot of ln [A] vs. time gives a straight line for a first-order reaction.D. Second-order rate equationE. A plot of 1/[A] vs. time gives a straight line for a second-order reaction.F. Zero-order rate equationG. A plot of [A] vs. time gives a straight line for a first-order reactionH. The concentration data is used to construct three different plots. Since the plot of ln [N2O5] vs. time gives a straight line, the reaction is first order.IX. Reaction Half-lifeA. The half-life (t1/2) for a reaction is the time taken for the concentration of a reactant to drop to half its initial value.B. For a first-order reaction, t1/2 does not depend on the starting concentration.C. The half-life for a first-order reaction is a constant.D. Radioactive decay is a first-order process. The half-life for a radioactive nucleus is a useful indicator of its stability.X. Collision Theory and ConcentrationA. The basic principle of collision theory is that particles must collide in order to react.B. An increase in the concentration of a reactant leads to a larger number of collisions, hence increasing reaction rate.C. The number of collisions depends on the product of the numbers of reactant particles, not their sum.D. Concentrations are multiplied in the rate law, not added.XI. Temperature and the Rate ConstantA. Temperature has a dramatic effect on reaction rate.B. For many reactions, an increase of 10°C will double or triple the rate.C. Experimental data shows that k increases exponentially as T increases. This is expressed in the Arrhenius equation:XII. Activation EnergyA. In order to be effective, collisions between particles must exceed a certain energy threshold.B. When particles collide effectively, they reach an activated state. The energy difference between the reactants and the activated state is the activation energy (Ea) for the reaction.C. The lower the activation energy, the faster the reaction.XIII. Temperature and Collision EnergyA. An increase in temperature causes an increase in the kinetic energy of the particles. This leads to more frequent collisions and reaction rate increases.B. At a higher temperature, the fraction of collisions with sufficient energy equal to or greater than Ea increases. Reaction rate therefore increases.XIV. Calculating Activation EnergyA. Ea can be calculated from the Arrhenius equationB. If data is available at two different temperaturesXV. Molecular Structure and Reaction RateA. For a collision between particles to be effective, it must have both sufficient energy and the appropriate relative orientation between the reacting particles.B. The term A in the Arrhenius equation is the frequency factor for the reaction.C. p = orientation probability factorD. Z = collision frequencyE. The term p is specific