Kinetics of the fading of phenolphthalein lab report

CHEM 132 Quantitative Chemical Kinetics Lab Report
Subject
Science

Course
CHEM 132

Department
CHEM

Question Description
Here are some questions about kinetic lab, the questions are in the report worksheet. The data document is attached below. Thank you!Chem 132 Quantitative Chemical Kinetics1,2,3 Spring 2020 INTRODUCTION Reaction Rates and Rate Laws We’ve looked at a wide range of chemical reactions and learned how to determine the relative concentrations of reactants and products at equilibrium. Regardless of where the final position of a chemical equilibrium lies, however, to ask how long it will take to reach equilibrium is an entirely different question. The rate at which a chemical reaction occurs depends on several factors: the chemical identities of the reactants, their concentrations, the temperature, and the presence of catalysts. Each of these factors can markedly influence the observed rate of reaction. Some reactions at a given temperature are very slow—the oxidation of H2(g) or gasoline is unquestionably spontaneous, but neither process proceeds appreciably at room temperature, even in a hundred years. (Add a lit match and it’s a different story!) Other reactions are essentially instantaneous. The precipitation of solid silver chloride when aqueous silver ions and chloride ions are mixed, and the formation of water when acidic and basic solutions are mixed are examples of extremely rapid reactions. In this week’s experiment we’ll study a reaction that proceeds at a moderate, relatively easily measured rate at room temperature so that we can quantitatively characterize the reaction kinetics. For a given reaction, reaction rate typically increases with an increase in the concentration of any reactant. For a general reaction, aA + bB → cC + dD (1) the reaction rate can be expressed as the change in the concentration of the products or reactants as a function of time: (2) Because the reaction rate is strictly positive, the negative sign for the reactant terms indicates that the concentration of those species decreases over time (they are being consumed), whereas the concentration of products increases (they are being produced). The reaction rate can also be expressed in terms of the concentration of the reactants by an equation we call the rate law for the reaction: Rate = k [A]m [B]n (3) Here m and n are generally, but not always, integers (0, 1, 2, or possibly 3); [A] and [B] are the concentrations of A and B; and k is a constant called the rate constant of the reaction. Note that the values of m and n can only be determined experimentally and are entirely unrelated to the stoichiometry of the reaction. The numbers m and n are called the orders of the reaction with respect to A and to B, respectively. For example, if m = 1 the reaction is said to be first order with respect to the reactant A. If n = 2 the reaction is second order with respect to reactant B. Winans, R; Brown, C. A. J. Chem. Educ. 1975, 52, 526-527. Nicholson, L. J. Chem. Educ. 1989, 66, 725-726. 3 Kildahl, N.; Varco-Shea, T. Explorations in Chemistry (Wiley: NY, 1996); 191-199. 1 2 1 Chem 132 Spring 2020 The rate law in Eq. 3 provides valuable insight into the underlying chemistry of the reaction, because the rate law (that is, the values of k, m, and n, which we determine by experiment) directly reflects the mechanism of the reaction. From the rate law, we can often determine how individual reactants break bonds and collide to form new bonds during the reaction, and the order in which that occurs. A rate law is thus a kind a microscope: it can inform us what is happening during the reaction at the level of individual atoms or molecules.