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Chemisty A level > Reaction Kinetics > Flashcards

Reaction Kinetics Flashcards

1
Q

What does kinetics mean?

A

things related to the rate of reaction

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2
Q

What is the rate of reaction?

A

the rate of change of concentration of a reactant or product with time

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3
Q

What are the units for rate?

A

moldm-3 s-1

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4
Q

What are the 2 ways that rate can be measured?

A
  1. samples taken at interval time points
  2. continuous monitoring of the reaction
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5
Q

How does a colorimeter work?

A

uses a filter to select light in a wavelength range where there is a big difference in strength of absorptio by the products compared to the reactants

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6
Q

What is the method of monitoring a reaction using colorimetry?

A
  1. select filter for an appropriate wavelength
  2. calibrate the colorimeter by measuring absorbance rate of standard solutions with known concs of the coloured substance
  3. plot a calibration curve of absorbance v conc
  4. start reaction in the sample cell of the colorimeter, measure absorbance rate continuosly
  5. use calibation curve to turn absorbance readings into conc readings
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7
Q

What is the definition of the rate equation?

A

the rate equation for a reaction shows how the rate depends on the concentrations of reactants

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8
Q

What is the generic rate equation?

A

Rate = K[A]^m [B]^n

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9
Q

What is K in the rate equation?

A

the rate constant

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10
Q

What is m/n in the generic rate equation?

A

the order of reaction with respect to the reactant

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11
Q

How do you calculate the overall order of reaction (generic)?

A

m + n
the sum of the separate orders

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12
Q

What is the definition of the rate constant?

A

a measure of the probability that a reaction will happen when the particles collide

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13
Q

What happens to K as the temp increases? and why?

A

K increases as the temp increases
because the proportion of reactant molecules (or ions) with energy greater than the activation energy increases

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14
Q

How does concentration and pressure affect K?

A

it doesnt have any affect on K

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15
Q

What is half life?

A

the time taken for the concentration of a reactant to fall to half its original value

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16
Q

What is the abbreviation for half life?

A

t 1/2

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17
Q

What is the rate equation for 0 order?

A

rate = K

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18
Q

What happens to the t1/2 of a 0 order reaction?

A

sucessive half-lives decrease

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19
Q

What are the units for K for 0 order?

A

the same as rate - moldm-3 s-1

20
Q

What is the rate equation for a first order reaction?

A

Rate = K[A]

21
Q

What happens to the t1/2 of a 1st order reaction?

A

successive half-lives remain constant

22
Q

How can you calculate the value of K from the t1/2 (t1/2 equation)?

A

K = ln 2 / t1/2

23
Q

What is the relationship between the [A] and the rate of a 1st order reaction?

A

they are directly proportional

24
Q

How would you find the value of K from a 1st order rate v conc graph?

A

the gradient = K

25
Q

What is the rate equation of a 2nd order reaction?

A

rate = K[A]^2

26
Q

What happens to the t1/2 in a 2nd order reaction?

A

successive half-lives increase

27
Q

What is the units of k for a 1st order reaction?

A

s-1

28
Q

What are the units of K in a 2nd order reaction?

A

mol-1 dm3 s-1

29
Q

What are the 2 ways rate can be found?

A
  1. measuring the change in a reactant mass/ conc over time
  2. measuring the change in a product mass/conc over time
30
Q

How can titrations be sed to find the rate of reaction?

A

small samples of reaction mixture can be removed at regular intervals
samples can be titrated to determine the conc of a product/reactant

31
Q

How can colorimetry be used to determine rate of reaction?

A

formation or depletion of a coloured species
measures the amount of light absorbed by solution = proportional to the conc of the coloured species

32
Q

What is the rate determining step?

A

the slowest step in a reaction pathway

33
Q

How do you find the order of A from using initial rates?

A

change the conc of A in the reaction A + B —> C
keep conc of B constant
if 1st order than proportion of increase in conc to the initial rate is equal
if 2nd order then the proportion of the initial rate is squared = doubling the conc of A will cause the inital rate to x4

34
Q

What effect does 0 order have on rate while changing the conc of an reactant?

A

has no effect on rate

35
Q

What effect does 1st order have on rate while changing the conc of an reactant?

A

increasing the conc of reactant by a factor of x increases the rate by the same factor of x

36
Q

What effect does 2nd order have on rate while changing the conc of an reactant?

A

increasing the conc of reactant by a factor of x increases the rate by a factor of x squared

37
Q

What do clock reactions find?

A

find an approximate value for the intitial rate of reaction by measuring the time it takes for a certain amount of product to form

38
Q

What is the general method for analysis of clock reactions?

A

times for colour change are measured for a range of different initial reactant concs = T
1/T is calculated

39
Q

What does the number of moles represent in a rate equation?

A

the number of moles of a substance is equal to the order of reaction for that substance

40
Q

How do you identify a catalyst from a reaction mechanism?

A

heterogneous catalyst = it will be used up and regenerated in a later step

41
Q

What happens to the rate of reaction when temp increases? (boltzmann distribution)

A

the proportion of molecules with an energy higher than the Ea
successful collisions occurr more frequently

42
Q

What happens to the rate constant (k) when temperature increases?

A

increases = K is related to the probability of successful collisions

43
Q

What is the arrhenius equation?

A

K = Ae (-Ea/RT)

A = pre-exponential factor
R = gas constant
e = e on calc

44
Q

What is the pre-exponential factor (A) ?

A

relates to the conentrations of reactants to the frequency of collisions
units are the same for rat constant

45
Q

What is the exponential term mean - e^ -(Ea/RT) ?

A

reflects the probability of a collision being successful = very temp dependent
it has no units

46
Q

How can you rearragnge the arrhenius equation to find the Ea from a graph?

A

ln K = (-Ea/R) x 1/T + ln A
—–> y = mx + c
gradient = -Ea/R
y intercept = ln A

Chemisty A level (28 decks)

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