Exam 2 Study Guide 1 Reaction Rate a The change in the concentration of a reactant or a product with time M s i b Over time reactants are going to products i Picture starting with a bucket of red balls next over time it is red and blue then it goes all the way to blue ii Reactants are consumed while products are formed 1 2 moles of C disappear for every mole D is formed iii iv 2C D 2 c What influences the rate of a reaction i Concentration 1 Molecules must collide to react 2 Increase molecules increase collisions increase rate ii Surface Area 1 2 Example iii Temperature iv Catalyst Increase frequency of collisions with an increase in surface area a A long chain has more surface area than a compact molecule 1 2 Increase in temperature increase in rate due to an increase in energy and frequency Increase the temp by 10 degrees C the rate doubles Increase the rate by decreasing the energy of activation 1 2 A catalyst makes the hill shorter so you can get to products faster 2 General Rate Expression a aA bB cC dD b c The whole thing is the rate expression d Example i e Example i ii The easiest way to solve this 1 A 0 024 M s O2 x 2 M s N2O5 1 M s O2 a 0 048 M s 2 B 0 024 M s O2 x 4 M s NO2 1 M s O2 a Negative NO2 because it is a reactant b 0 096 M s f Rate constant constant of proportionality between reaction rate and concentration of reactant 3 Rate Law a Expresses the relationship of the rate of a reaction to the rate constant and the concentrations of the reactants raised to some powers b 4 Reaction Order i The A and B means the concentration of A and B ii Reactants only iii X and y are the order of the reaction a Specify the relationship between the concentrations of reactants A and B and the reaction rate b Reaction is xth order in A c Reaction is yth order in B d Reaction is x y th order overall e Zero order is not included in the rate law f Example i How will the rate of the reaction change when the concentration changes by 1 2NO g O2 g 2NO2 g a Rate k NO 2 O2 2 A NO2 is doubled a Rate k 2 2 1 1 4 quadruples 3 B NO2 is halved 4 C O2 is doubled a Rate k 0 5 2 1 1 0 25 the rate a Rate k 1 2 2 1 2 doubles 5 D O2 is halved a Rate k 1 2 0 5 1 0 5 halves g Example h Example i Use given rate law to determine best answer for reaction 1 Rate k H2O2 2 I ii H2O2 aq 3I aq 2H aq I3 2H2O l 1 H2O2 is 2nd order I is first order H is 0th order 2 Reaction is 3rd overall n 2 1 0 3 i Chemical reaction between A and B is first order with respect to A 1st order with respect to B and 2nd order overall Fill in the blanks Experiment 1 2 3 Rate k A 1 B 1 Initial Rate M s 4 0 x 10 3 1 6 x 10 2 3 2 x 10 2 1 Step 1 4 0 x 10 3 M s k 0 20 1 0 050 1 Initial A M 0 20 0 80 0 40 Initial B M 0 050 0 050 0 20 2 Step 2 1 6 x 10 2 M s 0 4 M s A 1 0 050 1 3 Step 3 3 2 x 10 2 M s 0 4 M s 0 40 1 B 1 4 0 x 10 3 M s k 0 01 K 0 4 M 1 s 1 1 6 x 10 2 M s 0 02 A 1 A 0 80 3 2 x 10 2 M s 0 16 B B 0 20 i Example i Following data obtained at 25 degrees C What is the rate law expression and specific rate constant 1 2A g B g 3C g Experiment Initial A Initial B Initial rate of formation of C 1 2 3 Rate k A 1 B 1 0 10 0 20 0 10 0 10 0 10 0 20 2 0 x 10 4 4 0 x 10 4 2 0 x 10 4 ii Step 1 Where does A change and B stay the same 1 1 and 2 2 Can find A x A x A x rate 2 rate 1 0 20 0 10 x 4 0 x 10 4 2 0 x 10 4 3 Order 2x 2 x 1 1 1 and 3 iii Step 2 Where does B change and A stay the same 2 Can find B y B y B y rate 2 rate 1 0 20 0 10 y 2 0 x 10 4 2 0 x 10 4 3 Order 2y 1 y 0 iv Rate law expression rate k A 1 v Step 3 2 0 x 10 4 k 0 10 1 1 K 0 002 s 1 j Example i A certain chemical equation has given rate law 1 Rate k A 3 B 2 C 1 ii What are the units of the rate constant 1 K M n 1 x time 1 a N overall order 2 K M 4 1 x s 1 3 K M 3 x s 1 k M x s 0 order l m M 1 x s 1 2nd order S 1 1st order 5 Concentration and Time a Can be used to predict concentrations at any time b First Order Reactions i 1 ii Example 1 Ln A t 6 7 x 10 4 s 1 x 528 s ln 0 25 a A 8 8 x 60 528 s a b Ln A t 1 74 c eln A t e 1 74 d A t e 1 74 0 18 M b B ln 0 15 0 25 6 7 x 10 4 t a T 12 7 min c C 1 0 74 0 26 ln 0 26 1 00 6 7 x 10 4 t a b T 33 min iii First Order Half life 1 2 Concentration independent c Second Order Reactions i ii iii Example 1 2 To answer a a 1 A t 7 0 x 109 120 seconds 1 0 086 b 1 A t 8 4 x 1011 1 c Cross multiply d 1 8 4 x 1011 At e At 1 19 x 10 12 iv Half life of second order 1 d Zero Order Reactions i ii i ii f Summary e Pseudo First Order Reaction i Sometimes a second order reaction can appear as a first order reaction 6 Collision Theory of Reaction Rates a Must Collide i But not only collide they …
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