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A level Chemistry > Kinetics > Flashcards

Kinetics Flashcards

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1
Q

pressure =

A

Conc of gas

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2
Q

⭐ can’t have ? on x axos of energy profile diagram?

A

time. must be ‘progres of reaction’

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3
Q

don’t put ? on EPD

A

Double headed arrows

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4
Q

kinetics is about?

A

ROR

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5
Q

Ea =

A

the min. energy a particle must have to be involved in a successful collision

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6
Q

Rate of reaction =?

A

the change in conc of products/ reactants with time

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7
Q

the units of rate are?

A

moldm-3

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8
Q

how can rate be measured from a graph?

A
  • conc/time graph
  • draw tangent to curve, calculate gradient
  • draw tangent all the way to axis
  • make the angle either side of the tangent roughly the same
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9
Q

slope of the curve =?

A

rate

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10
Q

⭐ IROR =

A

AT 0 SECONDS

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11
Q

what is the relationship between conc and rate?

A

conc ∝ rate

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12
Q

how are orders of reaction always deduced?

A

From experimental data

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13
Q

the order of reaction is to do w ?

A

how changing the conc of 1 reactant affects the ROR

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14
Q

First order reactions?

A
  • x2 conc of reactant, rate does not change
  • Rate = k[r] to the power of 0
  • so rate is ∝ to [HCl]^0
    anything to the power of 0 is 1
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15
Q

First order reactions?

A
  • when conc of reactant x2, rate x2
  • Rate = k[HCl]^1
  • Rate ∝ [HCl]^1
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16
Q

Second order reactions?

A
  • when the conc of reactant doubles, the rate increases by 2^2 = 4
  • Rate = k[HCl] to the power of 2
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17
Q

Rate equation?

A

Rate = k[A][B] to the power of 0/1/2

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18
Q

if the reaction is first order?

A

don’t include that reactant in the rate equation

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19
Q

overall order?

A

just add indiv orders together

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20
Q

The rate constant, k, is

A

proportionality constant that relates rate to the conc

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21
Q

what do you have to work out for every single reaction?

A

units for k, just like we have to work out the units for the equilibrium constant

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22
Q

what is the impact of increasing temp on k?

A

Rate ⬆ and conc stays the same so ⬆ temp means that k has to ⬆.

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23
Q

when working out the units?

A

when bringing a unit to the top, change the signs

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24
Q

how do you work out the units for k ?

A

cancel units

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25
Q

k =

A

rate/ [reactants]

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26
Q

only include ? in the rate equation?

A

reactants not products

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27
Q

how do u know when a substance is a catalyst?

A

doesn’t appear in reaction but affects ROR

28
Q

how else can we tell the order of a reaction?

A
  • half life from a graph

- conc/time or conc/rate graph

29
Q

half life definition?

A

the time for the conc of a reactant to drop to half of its original value
t subscript 1/2/

30
Q

exam tip: half life

A
  • show clearly on the graph 2 half lives
  • calculation
  • explain which order
31
Q

Conc vs time graph: zero order

A

the [r] has no effect on time but conc decreases over time bc [r] is used up.
conc decreases at a constant rate.
STRAIGHT LINE

32
Q

Conc vs time graph: first order

A
  • as the conc x2, reaction time halves
  • conc halves at equal time intervals - constant half life
  • slight downwards curve
33
Q

Conc vs time graph: second order

A
  • as he conc x2, reaction time 1/4 so half life increases
  • conc rapidly decreases
  • downwards curve
34
Q

rate vs conc graph: zero order

A
  • reactant has no effect on rate

- horizontal line

35
Q

rate vs conc graph: first order

A
  • as the conc x2 the rate x2
  • as conc x3, rate x3
  • rate ∝ conc
  • proportional straight line
36
Q

rate vs conc graph: second order

A
  • as the conc 2z, rate 4x
  • rate ∝ conc^2
    exponential graph when rate vs conc
    but when rate vs conc^2, then straight line
37
Q

initial rates method (using experimental data)

A

if 2 reactants. look at when one is constant to get the rate for the other

38
Q

if 2 reactants, and both change ?

A

Work out the order for for, account for that change and deduce the order for the second (actually decent)

39
Q

when working out the mechanism,

A
  • TRY to make 1 of the products
  • cancel intermediate to get overall equation
  • reactions don’t have to make sense
  • check by cancelling
  • can only cancel something if it appears in the reactant and products
40
Q

what is a reaction mechanism?

A

the series of steps of a reaction

41
Q

the rate determining step?

A

the slow step.

42
Q

how can the molecules in the rate determining step be worked out?

A
  • from the rate equation
  • if a reactant appears in the rate equation, it will appear in the RDS
  • The order tells you how many particles to put into the RDS
    []^1 = 1 of that reactant, []^2 = 2 of that reactant
43
Q

the 2nd step of the mechanism must?

A

use up the intermediate

44
Q

Why might the initial rate of substances be different?

A

different molar ratios

45
Q

diradical =?

A

2 unpaired e-s

46
Q

what affects the value of the rate constant?

A

the temp

47
Q

What is natural log the inverse of?

A

exponential

48
Q

what can the Arrhenius equation do?

A

calculate the proportion of particles that can actually react

49
Q

In means

A

natural log of

50
Q

In k =

A

natural log of the rate constant

y axis

51
Q

A =

A

the pre-exponential factor

tells us about the frequency and geometry of collisions

52
Q

Ea=

A

Activate energy in J

53
Q

R =

A

the gas constant(data sheet)

54
Q

T =

A

temp in Kelvin

55
Q

y = mx + c in relation to Arrhenius equation

A 
Y = In K (y axis)
M = -Ea/ R, gradient 
x = 1/T in kelvin (x axis)
c = y intercept, natural log of A
56
Q

graph for arrhenius?

A
  • exponential
  • when the temp x2, the fraction of molecules w E ≥ Ea more than x2
  • so the relationship between rate constant and temp is NOT double
57
Q

when MUST you substitute into the arrhenius equation to get A?

A
  • when the x axis does not start at 0 (there’s a break)

- if it does, y intercept = inA

58
Q

alternative method to find k?

A

k = in 2/ half life

BUT THIS ONLY WORKS FOR FIRST ORDER REACTIONS

59
Q

Colorimetry:

darker solution…

A

more conc

60
Q

Colorimetry: purpose

A

In any reaction involving a coloured substance (either reacting or being produced), the reaction can be followed using a colorimeter

61
Q

Colorimetry: light

A
  • colour of light can be changed by selecting a paticiualrly coloured filter
  • complementary colour to the same used so the samle absorbs it
  • e.g. copper sulphate is blue so a red light is used bc red is absorbed
62
Q

Colorimetry: the more concentrated a solution is?

A

the more light it will absorb

63
Q

Colorimetry: The substance used has to…

A

change colour as the reaction occurs

64
Q

Colorimetry: what can u measure?

A
  • the amount of light absorbed as it passes through a solution - recorded as the absorption of a solution
65
Q

Colorimetry: how to get conc from absorbance?

A
  • plot calibration curve by making up known concs of the coloured solution and measuring the absorbanc of each under the same conditions as the experiment that u will do
  • plot absorbance against conc to get the CC
  • read off CC
66
Q

The rate constant always ?

A

STAYS THE SAME unless T changes

A level Chemistry (39 decks)

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