book kinetics Flashcards

1
Q

rate of reaction definition

A

rate at which reactants are converted into products

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2
Q

what is easured when measuring rate of a reaction

A

measure formation of products

consumption of reactants

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3
Q

what is a kinetics profile

A

graph of conc against time that shows how fast conc changes as the reaction proceeds

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4
Q

what do we plot when looking at rate of reaction

A

concentration against time

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5
Q

rate of reaction at a particular time

A

find the gradient (y/x)

rate must be positive

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6
Q

initial rate is the

A

rate at 0 time

tangent on 0 + gradient at 0

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7
Q

units for rate of reaction if conc is in moldm-3

A

mol dm-3 s-1

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8
Q

units for rate of reaction of a gas whrn units are Pa

A

Pa s-1

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9
Q

gradient of line or rate at particular time in terms of differentials

A

d[a] / dt

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10
Q

what affects the rate of reaction

A

conc
temp
catalyst

surface area of solid
radiation intensity
solvent nature

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11
Q

what is rate constant k

A

constant that relates the speed of the reaction to a certain condition, normally temp.

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12
Q

does rate law / rate equations use reactant conc or product conc

A

reactant conc

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13
Q

rate law / rate equation example

A

k [rea] [rea]

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14
Q

why do we need integrated rate equations

A

rates of reaction cannot be measured directly.

exp data usually consists of pro and rea conc measurements at different times.

integrated rate laws give an expression that shows how conc varies with time.

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15
Q

IRL of conc of rea A at time t

A

[A]t

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16
Q

IRL of conc of rea A at the start of the rea

A

[A]0

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17
Q

IR for first order reaction:
A -> B

A

ln [A]t = ln[A]0 - kt

if k and ln[A]0 are known, conc of A at any time can be found

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18
Q

what do u plot on the graph for 1st order rea

A

ln[A] against time

gradient = -k

19
Q

IRL straight line edition for 1st order

A

ln[A]t = -kt + ln[A]0

y = mx + c

20
Q

IRL for second order rea

A

1/ln[A]t = 1/ln[A]0 + 2kt

21
Q

IRL straight order version for 2nd order

A

1/ln[A]t = 2kt + 1/ln[A]0

22
Q

what do we plot for a 2nd order rea

A

1/[A] against time

2k = gradient

23
Q

half life definition

A

t 1/2

time taken for conc of reactant to fall to half its initial value

24
Q

half life equation first order

A

t1/2 = ln(2) / k

25
half life equation 2nd order
t1/2 = 1 / 2k [A]0
26
how must a rate equation be determined
experiments to see how rate depends on conc of each reactant. in order to find the order.
27
if the conc change of a reactant has no effect on the rate it isss
0th order doesnt appear in the overall rate equation
28
what is the reactions mechanism
series of elementary steps that make up the whole reaction (complex reactions, reactions with more than one step)
29
isolation method
put one reactant in excess so its initial conc is the same as its conc throughout the reaction. find the effect of 1 rea conc on rate, then switch and repeat for the other reactant. these will give us pseudo rate constants.
30
initial rates method
gradient is found for t=0 - ror at start of reaction initial rate repeat for different starting concentrations conc is plotted against time conc ust be monitored throught and plotted in order to get a graph to find t=0
31
each elementary step has its own
rate constant
32
the rate determining step is the
slowest step slowest mechanism
33
what is a concerted reaction
when rea turns into pro in a single step
34
if a rate constant has a larger value that means the reaction is
faster
35
k is .... for a given temp
constant
36
rate is .... for a given temp
not constant usually changes during the reaction.
37
what does the term e -Ea/RT mean
fraction of collisions that have the required energy
38
what happens to e -Ea/RT as temp increases
the value gets smaller, it gets closer to 0 e0 = 1 1 means all collisions have enough energy. so k = A
39
what is A in arrhenius
pre exponential factor same units as k rate constant value if all the collisions have enough energy to overcome the energy barrier aka the activation energy.
40
what is the arrhenius equation
k = Ae -Ea/RT equation that describes how the rate constant varies with temperature
41
what is Ea
activation energy Jmol-1 energy barrier reactants need to overcome in order to form products
42
how does rate constant increase with temp
a greater fraction of the reactant molecules have enough energy to pass over the energy barrier. more reaction molecules have or have above the Ea value.
43
what happens in the collision theory
used to find approx value of A. for a reaction to occur, 2 molecules must collide with a certain minimum kinetic energy. the Ke must be equal to or larger than the Ea.
44
what is kinetics
study of the rates of chemical reactions