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chemistry 1302 gen chem 2 > chapter 11: chemical kinetics > Flashcards

chapter 11: chemical kinetics Flashcards

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1
Q

what is kinetics

A

concerned w/ the speed rates of rxns

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2
Q

what is rate

A

changes in quantity in a given period of time

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3
Q

what is thermodynamics

A

tells the direction and extent of the reaction

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4
Q

what is a state function

A

independent of the path

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5
Q

thermodynamics has nothing to do with

A

kinetics

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6
Q

how can you determine the rate of reactions

A

monitoring the change in concentration
- reactions slow down every time

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7
Q

what is the instantaneous rate

A

the slope of a line tangent to the curve at any point

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8
Q

what is the initial rate

A

the instantaneous rate, t= 0

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9
Q

what is a rate law

A

shows how the rate depends on the concentrations

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10
Q

what is k

A

the rate constant

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11
Q

how do you determine the exponents

A

determined by the experiment

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12
Q

what are the rate law exponents

A

0,1,2

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13
Q

what is the overall reaction order

A

the sum of the orders w/ respect to each reactant in the rate law

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14
Q

how do you write the rate

A

use the reactants k[A]^a[B]^b

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15
Q

what are the units of rate constant

A

M^-1,S^-1

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16
Q

what is zero order

A

changing conc. has no effect on the rate

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17
Q

first order

A

rate changes by the same factor as the conc( doubles the initial concentration doubles the rate)

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18
Q

what is second order

A

the rate changes by the square of the factor the concentration changes
- doubling the initial concentration quaduples the rate

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19
Q

what is another name for rate laws

A

differntial rate laws
- used to calculate reaction rates when given reactant conc.

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20
Q

what is integrated rate laws

A

used to calculate the amount of reactants left after a certain amount of time has passed

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21
Q

what is the first order reaction equation

A 
ln[At] = -kt+ ln[A0] 
y = mx + b
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22
Q

what are some characteristics of zero reactions

A

-rate=k[A]^0\
- doesn’t depend on concentration
- 2^0 =1, 3^0 -1
- M^1t^-1
equation: -kt + [A0]
slope = -k

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23
Q

what can you use to find the order of a reaction depending on the exponent

A

M^1-n t^-1

24
Q

what is half life t1/2

A

time required for one half of a reactant to react
[A] @ 1/2 is one half the original then [At] = 0.5[A0]

25
Q

what is the first order reaction 1/2 life equation

A
  • does not depend on the initial concentration
  • 0.693/k = t/1/2
26
Q

what is the second order reaction equation

A

1/[At] = kt + 1/[A0]

y = mx + b

27
Q

what is the half-life equation for second-order reactions

A

1\k[A0] = t1/2

28
Q

what is the equation for a zero order 1/2 life equation

A

[A0] /2k

29
Q

when do zero order reactions most likely occur

A

when a substance such as a metal surface or enzyme is required for a reaction to occur

30
Q

what is the collision model

A

accounts for the observed characteristics of reaction rates

  • molecules need to collide to react
31
Q

what are the 4 factors that affect rate

A
  1. concentrations of reactants
  2. physical state of reactants
  3. temperate
  4. structure and orientation of reacting particles
32
Q

how concentrations of reactants affect rate

A
  • increase in concentration = increase that the mlcls will collide = increase in rate

-reducing volume / increasing pressure on gas = concentration increase

33
Q

phyisical state of reactants and rate

A
  • reactants that are more homogenous the faster it will react
  • reactants in diff. phases = limited area of contact
  • limited area = reactions that involve solids proceed faster if the surface area of the solid is increased
34
Q

temperature and rates

A
  • higher temp = more KE = molecules will collide more often and w/ greater energy

  • rate increases bc of temperature rising
35
Q

structure and rates

A
  • greater frequency of collisiosn = greater rate of reaction
36
Q

for a collision to lead to a rxn what needs to occur

A

has to have enough energy to stretch bonds to form new bonds in other proper locations

37
Q

what are effective collisions

A

collisions in which the 2 conditions are met (greater frequency + lead to reaction)

  • increase in EFFECTIVE collision = faster rate
38
Q

what is activation energy

A
  • Svante Arrhenius
  • energy that molecules possess in order to react
39
Q

what is a reaction coordinate diagram

A
  • very top of the hill is the transitions tate
  • right = products
  • left = reactants
40
Q

what is the activated complex and activation energy barrier

A
  • activated complex: species present at the transition state
  • activation energy barrier= the energy gap between the reactants and the activated complex
41
Q

difference in Ea of the forward vs. reverse

A

Ea is always higher for endothermic proc3sses

42
Q

what is the arrhenius equation

A

ln k = -Ea/R(1/T) + Ln A

  • T = temp in kelbin
  • Ea = activatio energy
  • R = 8.314 J/ mol k

A = frequency factor

43
Q

what is a frequency factor

A

the likelihood that collisions would occur w/ proper orientation for reaction

44
Q

what arrhenius equation is used to evauluate 2 or more temps

A

ln k1/k2= Ea/R(1/t2 - 1/T1)

45
Q

what does a balanced equattion not tell us

A

how the reaction occurs

46
Q

what is the reaction mechanism

A

the sequence of events that describes the actual process of how reactants turn into products

47
Q

what is each step known as in a reaction mechanism

A

elementary reaction

48
Q

what is an INTERMEDIATE

A

substance that is formed first as a product then consumed as a reactant

49
Q

what is molecularity

A

the number of reactants molecules in an elementary step

50
Q

what are the different molecularitys

A
  • unimolecular = k[A]
  • bimolecular = 2
  • termolecular = 3
51
Q

what happens in a mulistep process

A

one process will be slower than the others and this is the rate determining step

52
Q

why is the slowest step the rate determining ste[

A

slowest step has the largest activation energy

53
Q

what is a catalyst

A

a substance that changes the rate of a reaction w/out being permanently consumed

  • consumed in an early step in the reactants and then produced in the products at a later step
54
Q

what is a homogenous catalyst

A

present in the same phase as the reactant molecules

55
Q

what is a heterogenous catalyst

A

present in a different phase than the reactant molecules

  • catalyst can speed up a reaction by holding the reactants together and helping to break bonds
56
Q

what is an enzyme

A

protein molecules that catalyze biological reactions

  • active site: the place of the reaction
57
Q

what is sibstrate and the lock and key model

A
  • substrate: substances that undergo reactoin at the site
  • lock and key model: enzymes are specific and they fit inside certain substrates

chemistry 1302 gen chem 2 (10 decks)

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