week one notes
week one notes CHM 116 Cabirac
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This 3 page Class Notes was uploaded by Alexandra Votaw on Monday January 19, 2015. The Class Notes belongs to CHM 116 Cabirac at Arizona State University taught by Dr. Cabirac in Spring2015. Since its upload, it has received 147 views. For similar materials see CHM116- general chemistry II in Chemistry at Arizona State University.
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Date Created: 01/19/15
Chemistry 116 Notes week ofJanuary 13 2015 CHAPTER 14 CHEMICAL KINETICS General questions for the chapter 1 Does a chemical reaction occur 2 How far to completion does a reaction occur 3 How fast is a reaction reaction rates Factors That Affect Reaction Rates 1 Temperature higher temp molecules move fastermore frequent collisions w enough energy faster reaction rate 2 Concentration of Reactants more reactants more frequent collisions faster reaction rate 3 Physical State of Reactants reactants in states that make most contact ie solid in water more frequent collisions faster reaction rate All three above related to collision model Reaction Rate refers to how fast a reaction is occurring Usually measured by a change in the concentration of reactants or concentration of products over time Rate change in the concentration of some reactant quotAquot divided by the change in time Rate AAAt Rate the nal concentration of reactant A minus the initial concentration of reactant A divided by the nal time minus the initial time Rate Af Ai tf ti Units usually measured in molesLs or Ms molarity unit time 0 Can also use the change in pressure change in time instead of concentration There are two ways to measure the reaction rate the speed at which products appear the speed at which reactants disappear Example Br2aq HCOOHaq gt ZBraq 2Haq CW9 When Br2 is broken up it changes the opacity of the solution it is in Therefore its concentration at the beginning and throughout a reaction can be measured through spectroscopy Instantaneous rate rate for a speci c instance in time Initial rate instantaneous rate at t0 Rate kreactants hard brackets indicate concentration Rate constant k ratereactants REACTION RATESSTOICHIOMETRY For reactions such as aA bB CC dD where the lower case letters represent stoichiometric coef cients and the upper case letters represent reactants and variables the reaction rate expression is rate expression 1AAaAt 1ABbAt 1ACcAt 1ADdAt Examples 2A B Rate AA2At ABAt CH4lg 2029 DC029 2Hzolg Rate ACH4At A022At AC02At AH202At If ACH4At 48 X 10 2 Ms What is AH20At Rate ACH4At AH202At Rate 48 x 102 Ms AH202AtX2 D Rate Law expresses the relationship of the rate of the reaction to the rate constant K and the concentration of one or more reactants raised to some powers For the equation aA bB cC dD rate KAXBY where x and y can equal 0 1 2 and rarely 3 What does rate law tell us reaction is Xth order in A reaction is Yth order in B reaction is XYth order overall 0 The rate law tells us how the rate of a chemical reaction depends on the concentration of one or more of the reactants To determine the units for the rate constant K for 1St order reactions units for K s for 2nCI order reactions units for K M s for 3rd order reactions units for K M 2 s Rate laws can only be determined experimentally