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Kinetics Flashcards

(63 cards)

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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
Autocatalysts
Product of reaction acts as catalyst for same reaction Increase product amount, increase ROR
26
Heterogeneous catalysts (5)
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
catalytic converters
CO, NO, Unburnt HCs —> less harmful gases Platinum, palladium, rhodium Honeycomb structure, increase SA
28
Heterogenous catalyst poisoning
Cling to catalyst surface stronger than reactant Prevent reaction
29
Catalyst economic benefits
Quicker product Less energy than high temperatures Direct reaction to more useful products
30
Rate equation
Relationship between chemical reaction rate and reactant concentration Rate = k[A] *x[B]*y K changes units Rate: mol/dm*3/s
31
K size and rate relationship
K, large, fast K, small, slow
32
Order 0 effect and graphs
No effect on rate by conc Conc vs time: SL down Rate vs conc: horizontal line
33
Order 1 effect and graphs
Linear effect on rate by conc Conc vs time: curved line down Rate vs conc: SL up
34
Order 2 effect and graphs
Square effect on rate by conc Conc vs time: curved line down (steeper than order 1) Rate vs conc: urged line up
35
Half life
Conc/time graph Halve y axis increments Order 0: decrease Order 1: constant Order 2: increase
36
Rate constant k
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
Order
Power of reactant in rate equation
38
Overall order
Sum of powers of reactant Concs in rate equation
39
Identifying rate equation (3 methods)
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
Iodine clock equations
H2O2 + 2I- + 2H+ —> I2 + 2H2O I2 + 2S2O3*2- —> 2I- + S4O6*2- CH3COCH3 + I2 —> CH3COH2I + H+ + I-
41
Iodine clock steps
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
Rate determining step (3)
Slowest step in reaction mechanism Rate of overall reaction Species in RDS are in rate equation (expect intermediates)
43
Reaction mechanism
Series of steps where reactants become products in chem reaction
44
SN2 (7)
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
SN2
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
Secondary haloalkane rate equation
Provided Indicates no. Molecules in RDS
47
Activation energy equation
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
Activation energy graph calulculations
LnK/(1/T) SLG = -Ea/R ROR inversely proportional to t ROR proportional to 1/T 1/t or k can be used
49
Activation energy assumptions
A constant Less valid over larger scales More frequent collisions, insignificant effect on rate
50
Reversible reaction
Products of left to right can react to reform reactants
51
Closed system
Exchange energy with surroundings but not mass
52
Chemical equilibrium
Closed system where forward/backward rate are equal. No net conc/observable property change
53
Equilibria equations
Can be written either way, refer to substance NOT left/right
54
Kc
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
Kc and states
Varying concentrations (aqueous/gases) Solids - conc fixed by density, excluded Liquids - fixed density/conc, excluded
56
Multiple liquids and Kc
Separate layers - fixed density/conc, excluded Solution - dissolved, varied conc, included Water - reactant + solvent, assume excess, exclude
57
Setting up an equilibria reaction
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
Kp use
Gases Pressure and conc are proportional Define equilibria in terms of pressure Partial pressure of each mixture gas
59
Kp expression
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) PC*c PD*d (products)/ PA*a PB*b (reactants)
60
Starting a Kp expression
Initial sums to mtotal Find Equm amounts using mol ratios Divide by mtotal Get Px
61
Pressure effect
A —> 2B (FbPtot)*2 / FaPtot Cancel Fb*2 x Ptot / Fa Increase Ptotal, decrease fraction, decrease Fb, increase Fa, backward equilibria shift
62
Temperature effect
Forward Endo, increase temp, increase K, favour RHS Forward exo, increase temp, decrease K, favour LHS
63
Rate effect
No relationship between Equm position and ROR Catalyst doesn’t change Equm position, speeds reaction up Increase both reactions equally

Chemistry (24 decks)

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