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Chemistry > Kinetics > Flashcards

Kinetics Flashcards

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1
Q

Rate of reaction equation and units (4)

A

Change in conc/time for change to occur
Mol/dm3/s
How fast a reactant is used up
How fast a product is formed
Gradient = change in y/change in x of tangent

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2
Q

What 3 things are required for particles to react

A

Collide
Enough NRG
right orientation

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3
Q

Steric factor

A

Atom group shapes influence reaction

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4
Q

Steric hindrance

A

Large atom group can get in the way of attacking species

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5
Q

Primary vs tertiary haloalkane reactions

A

SN2: primary, halogen dissociates and nuc joins
SN1: tertiary, halogen dissociates then nuc joins
Secondary: mixture

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6
Q

Activation energy

A

Minimum KE needed for particles to react/break reactant bonds

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7
Q

3 features of an activation energy curve

A

Bonds stretched
Parts have enough energy to break bonds
Separate parts can’t exists alone so form new bonds

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8
Q

Which states does the Maxwell Boltzmann theory apply to

A

Ga/liquid
Some slow
Some fast
Most in between

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9
Q

Maxwell Boltzmann theory

A

No particles have 0 KE
most have intermediate
No upper limit
Area under curve = total no. Particles

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10
Q

Maxwell Boltzmann graph features (5)

A

Fraction of particles with E NRG vs NRG E
Mode = peak
Mean = just past peak
Ea = line
X axis and line don’t touch

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11
Q

Name 8 methods of determine rate of reaction

A

Mass
Volume
Precipitate
Ph
Colorimetry
Clock reactions
Titrations
Electrical conductivity

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12
Q

Gas volume practical method (3)

A

Gas syringe, conical flask, reaction mixture, bunged delivery tube
Ideal gas equation

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13
Q

Change in mass practical method (2)

A

Digital balance, cotton wool bung (gas lost, no pressure)
Carbonate, H2 mass too small to record

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14
Q

Colorimetry practical method (4)

A

Light source, filter, sample tube, light meter
Accurate, quantitative measurement
Propanone + iodine
Brown —-> colourless

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15
Q

Precipitate practical method (3)

A

Less precise than colorimeter
Bscure black cross
Subjective

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16
Q

Ph practical method (2)

A

UI
H+ reacting/produced

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17
Q

Electrical conductivity practical method (2)

A

AC
Total no./type of ions in reaction changes

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18
Q

Clock reactions practical method (2)

A

Make oodine
Solution turns blue/black

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19
Q

Titrations practical method (4)

A

Pipette aliquots at reg intervals
Quench reaction (ice bath + carbonate)
Titrate aliquot against reac/prod
Find conc

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20
Q

Temperature effect on ROR

A

Increase temp
Increase KE
Increase speed
Increase frequency/success of collisions
Increase proportion of particles with Ea +
Increase ROR

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21
Q

Concentration effect on ROR

A

Increase conc
Increase no.particles/volume
Increase frequency/success of collisions
Increase ROR
Gas/pressure has the same effect
No change in proportion of particles in relation to Ea

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22
Q

Surface area effect on ROR

A

Olids
Increase no. Exposed particles
Increase frequency/success of collisions
Increase ROR

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23
Q

Catalyst effect on ROR

A

Increase ROR
Unchanged catalysts
Lower Ea, alternative reactant pathway
Don’t change Equm or enthalpy change
Increase proportion of particles with Ea +

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24
Q

Homogenous catalysts (4)

A

Same physical state as reactants
Catalyst + reactants —> intermediates —> products + catalyst
Ea to make intermediate < Ea to make products
Catalyst overall unchanged

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25
Q

Autocatalysts

A

Product of reaction acts as catalyst for same reaction
Increase product amount, increase ROR

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26
Q

Heterogeneous catalysts (5)

A

Diffrent physical state to the reactants
Reactants absorb onto SA of catalyst
Reaction bonds weakened/break
Radicals form —> new molecules —> desorb
Absorption —> reaction —> desorption

27
Q

catalytic converters

A

CO, NO, Unburnt HCs
—> less harmful gases
Platinum, palladium, rhodium
Honeycomb structure, increase SA

28
Q

Heterogenous catalyst poisoning

A

Cling to catalyst surface stronger than reactant
Prevent reaction

29
Q

Catalyst economic benefits

A

Quicker product
Less energy than high temperatures
Direct reaction to more useful products

30
Q

Rate equation

A

Relationship between chemical reaction rate and reactant concentration
Rate = k[A] x[B]y
K changes units
Rate: mol/dm*3/s

31
Q

K size and rate relationship

A

K, large, fast
K, small, slow

32
Q

Order 0 effect and graphs

A

No effect on rate by conc
Conc vs time: SL down
Rate vs conc: horizontal line

33
Q

Order 1 effect and graphs

A

Linear effect on rate by conc
Conc vs time: curved line down
Rate vs conc: SL up

34
Q

Order 2 effect and graphs

A

Square effect on rate by conc
Conc vs time: curved line down (steeper than order 1)
Rate vs conc: urged line up

35
Q

Half life

A

Conc/time graph
Halve y axis increments
Order 0: decrease
Order 1: constant
Order 2: increase

36
Q

Rate constant k

A

Constant of proportionality
Same for any reaction at a specific temp (increase/decrease)
Units vary depending on overall order of rate equation (make k subject, insert units and cancel)
Doesn’t change with conc/pressure
Changes with catalyst (increases)

37
Q

Order

A

Power of reactant in rate equation

38
Q

Overall order

A

Sum of powers of reactant Concs in rate equation

39
Q

Identifying rate equation (3 methods)

A

Half lives
Rate/conc graphs (conc/time, tangents, find gradients, rate/conc, graph shape)
Initial rate (gradient of conc/time graph, all reactant Concs are known, compare initial Concs and rates)

40
Q

Iodine clock equations

A

H2O2 + 2I- + 2H+ —> I2 + 2H2O
I2 + 2S2O32- —> 2I- + S4O62-
CH3COCH3 + I2 —> CH3COH2I + H+ + I-

41
Q

Iodine clock steps

A

Continuous
H2SO4 vol/conc
Distilled water + starch
KI vol/conc
Na2S2O3 conc/vol
Swirl
H2O2 conc/vol
Time
Colorless —> blue/black
Repeat and vary KI vol
Quench aliquots and Titrate

42
Q

Rate determining step (3)

A

Slowest step in reaction mechanism
Rate of overall reaction
Species in RDS are in rate equation (expect intermediates)

43
Q

Reaction mechanism

A

Series of steps where reactants become products in chem reaction

44
Q

SN2 (7)

A

Nucleophilic substitution
2 molecules in RDS
Primary haloalkanes
1 step mechanism
RX breaks and COH forms
Unstable carbocation (not true intermediate)
1 methyl group (low steric hindrance, attack immediately)

45
Q

SN2

A

Nucleophilic substitution
1 molecule in RDS
Tertiary haloalkanes
2 step mechanism
RX breaks (RDS) THEN COH forms
Stable carbocation (true intermediate)
3 methyl group (high steric hindrance, attack slowly)

46
Q

Secondary haloalkane rate equation

A

Provided
Indicates no. Molecules in RDS

47
Q

Activation energy equation

A

K = Ae*(-Ea/RT)
LnK = lnA - Ea/RT
LnK = constant - (Ea/R) x (1/T)
K: rate constant
A: scaling factor
E: natural log
R: 8.31
T: temperature

48
Q

Activation energy graph calulculations

A

LnK/(1/T)
SLG = -Ea/R
ROR inversely proportional to t
ROR proportional to 1/T
1/t or k can be used

49
Q

Activation energy assumptions

A

A constant
Less valid over larger scales
More frequent collisions, insignificant effect on rate

50
Q

Reversible reaction

A

Products of left to right can react to reform reactants

51
Q

Closed system

A

Exchange energy with surroundings but not mass

52
Q

Chemical equilibrium

A

Closed system where forward/backward rate are equal. No net conc/observable property change

53
Q

Equilibria equations

A

Can be written either way, refer to substance NOT left/right

54
Q

Kc

A

Equilibrium constant
[C]c [D]d (products)/ [A]a [B]b (reactants)
Reverse direction, 1/Kc
Units vary, cancel and simplify
0> greater left conc
0< greater right conc

55
Q

Kc and states

A

Varying concentrations (aqueous/gases)
Solids - conc fixed by density, excluded
Liquids - fixed density/conc, excluded

56
Q

Multiple liquids and Kc

A

Separate layers - fixed density/conc, excluded
Solution - dissolved, varied conc, included
Water - reactant + solvent, assume excess, exclude

57
Q

Setting up an equilibria reaction

A

Specified mols
Left to achieve Equm
Find Equm mols
Use balance ratios
Use total vol —> Kc/concs
No unit cases don’t need volume, just use moles as they cancel out

58
Q

Kp use

A

Gases
Pressure and conc are proportional
Define equilibria in terms of pressure
Partial pressure of each mixture gas

59
Q

Kp expression

A

Ptotal = sum of all mixture gas partial pressures
F = proportion of fraction of moles of mixture gas
Pa = Ptotal x Fa
Unit = atm (100,000 Pa)
PCc PDd (products)/ PAa PBb (reactants)

60
Q

Starting a Kp expression

A

Initial sums to mtotal
Find Equm amounts using mol ratios
Divide by mtotal
Get Px

61
Q

Pressure effect

A

A —> 2B
(FbPtot)2 / FaPtot
Cancel
Fb2 x Ptot / Fa
Increase Ptotal, decrease fraction, decrease Fb, increase Fa, backward equilibria shift

62
Q

Temperature effect

A

Forward Endo, increase temp, increase K, favour RHS
Forward exo, increase temp, decrease K, favour LHS

63
Q

Rate effect

A

No relationship between Equm position and ROR
Catalyst doesn’t change Equm position, speeds reaction up
Increase both reactions equally

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