Chemical Kinetics Report.docx - Chemistry Lab 114 R5...

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Chemistry Lab 114 – R5Chemical Kinetics: Rate Constants and Activation EnergyPurposeThe purpose of this experiment is to examine the rate of a first order chemical reaction at twodifferent temperatures, determining the rate constant of the reaction at each temperature, in orderto determine the activation energy of the reaction. The reaction of interest in this experiment isthat between a hydroxide solution and the compound phenolphthalein (C20H14O4). TheoryThe theory behind this experiment is to study the change in the absorbance of thephenolphthalein solution as a function of time in order to calculate the reaction rate constant attwo different temperatures. These reaction rate constants can then be utilized to calculate theoverall activation energy of the reaction. This is the more convenient way to determine the rateof reaction and the corresponding rate constant, since the property of absorption is directlyproportional to the concentration as a function of the elapsed time. In this experiment,absorbance is defined as a measure of the amount of light of a certain wavelength that isabsorbed by a solution and is measured by a spectrophotometer. The wavelength used in thisexperiment is 552 nanometers. Absorbance is related to the concentration of the phenolphthaleinabsorbing solution by the Beer-Lambert law, which states that the absorbance of thephenolphthalein solution is directly related to the concentration of the phenolphthalein solution.Therefore, following the absorbance as a function of time reflects what is also happening to theconcentration of the phenolphthalein as a function of time, which is why this method is valid fordetermining the rate of the reaction. The rate of the reaction can be calculated if the log of theabsorbance measures of the phenolphthalein solution are plotted against time, since the sloperepresents the rate constant of the reaction. When the two rates of reaction for the two differenttemperatures are plugged into a rearranged version of the Arrhenius equation, the value of theactivation energy of the reaction can also be calculated.

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Term
Fall
Professor
N/A
Tags
Kinetics, Chemical reaction, Reaction rate constant, phenolphthalein solution, Phenolphthalein Compound

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