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chem 12 > reaction kinetics (unit 1) > Flashcards

reaction kinetics (unit 1) Flashcards

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1
Q

as a reaction proceeds, the reactants ____ while the products _____

A
  • decrease, increase
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2
Q

rate

A
  • change in amount of reactant or product/time
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3
Q

reaction kinetics

A
  • study of rxn rates + factors that affect rates
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4
Q

expressing reaction rates

A
  • quantity of product formed/ time

- quantity of reactant consumed/ time

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5
Q

what changes will you find in amounts of gas, liquids, solids and aqueous solutions?

A
  • gas = change in volume
  • liquids/solids = change in mass
  • aqueous solutions = change in concentration
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6
Q

ionic form

A
  • shows that some rxns have some ions that don’t change concentration
  • to write COMPLETE ionic, dissociate all AQ compounds and leave as is
  • to write NET ionic, dissociate all AQ compounds and get rid of stuff that is the same on each side
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7
Q

coefficient ratios

A
  • only proportional to MOL/S

- when other units used, you must convert to mol (ex/ the question gives you CO2 but you need to find O2)

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8
Q

on mass of container + contents vs time graph, the rate equals the ___

A
  • slope, which is amount vs time
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9
Q

for a changing rate on a mass of container + contents vs time graph, how can we express it?

A
  • draw straight line by curved line to get average

- draw tangent for average rate at a certain time interval

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10
Q

monitoring colour changes

A
  • only in rxns where coloured reactant is consumed or new coloured product formed
  • colour intensively can be measured quantitatively w/spectrophotometer
  • rate = change in colour intensity/ time
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11
Q

monitoring temp changes

A
  • in exothermic rxn, temp of surroundings increases
  • in endothermic rxn, temp of surroundings decreases
  • measured in insulated container (calorimeter), r = change in temp / time
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12
Q

monitoring pressure changes

A
  • if more moles of gas in product, pressure increases
  • if more moles of gas in reactants, pressure decreases
  • if equal MOG, pressure doesn’t change
  • rate for constant volume= change in pressure/time
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13
Q

7 ways to monitor reaction rates

A
  • colour change
  • temp change
  • pressure change
  • volume change
  • mass change
  • molar concentration change of specific ions
  • acidity change
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14
Q

monitoring volume changes

A
  • ex/ if more gas is produced in a balloon, the volume increases
  • under constant pressure, rate = change in volume/time
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15
Q

monitoring mass changes

A
  • if only one solid is used up, remove it periodically and weigh it
  • if one gas is produced and escapes, measure mass of what’s left in container
  • rate = change in mass of container + contents / time
  • ALSO: don’t measure mass of aq substances separately since they are mostly water
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16
Q

monitoring changes in molar concentration of specific ions

A
  • concentration of specific ion can be measured w/spectrophotometer or periodically taking samples and titrating
  • rate = change in conc of specific ion/time. make sure to CHANGE INTO IONIC FORM FIRST
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17
Q

monitoring changes in acidity

A
  • rate = change in pH / time
  • measured w/pH meter
  • pH is a measure of acidity
  • if hydrogen is a reactant, its concentration will decrease so pH will increase
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18
Q

is rate of reaction always positive?

A
  • yes, always!!!
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19
Q

homogenous rxn

A
  • all reactants are in the same phase (don’t consider products)
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20
Q

heterogenous rxn

A
  • more than 1 phase in reactants
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21
Q

5 factors that affect both homo and hetero rxns

A
  • temp
  • concentration of reactants
  • pressure
  • nature of reactants
  • catalysts/inhibitors
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22
Q

temp on homo/hetero rxns

A
  • as temp increases, rate increases
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23
Q

concentration of reactants on homo/hetero rxns

A
  • as conc of 1 or more reactant increases, rate increases

- partial pressure of a gas (pressure exerted by that gas in a mixture of gases) increases w/conc

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24
Q

pressure on homo/hetero rxns

A
  • affects rxns w/gases in reactants
  • as pressure increases, rate increases
  • decrease in volume of container increases pressure (therefore rate)
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25
Q

nature of reactants on homo/hetero rxns

A
  • rate depends on how strong + how many bonds in reactants need to be broken
  • covalent bonds are generally strong + slow to break down
  • when many bonds have to be broken/many new bonds must form, rate is low
  • simple electron transfer + ppt rxns are fast, acid base (proton transfer) is intermediate
  • aq is fastest phase, solid is slowest, gas + liquid are intermediate
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26
Q

catalysts/inhibitors on homo/hetero rxns

A
  • catalyst: substance which can be added to increase rxn rate without being consumed
  • inhibitor: substance which can be added to reduce rxn rate (can combine w/catalyst/reactant + prevent it from reacting). ex/ sunscreens, poisons, organophosphates (Diazinon), antibiotics, antidepressants
27
Q

surface area on hetero rxns

A
  • only affects hetero rxns
  • when 2 dif phases react, rxn can only take place on surface
  • increase SA by cutting solid into smaller pieces
28
Q

examples of body chemistry using control of rxn rates

A
  • metabolism
  • fever can destroy bacteria
  • neurotransmitters = awareness + sleep
  • hormones = messengers (adrenaline, sex hormones)
  • catalysts = enzymes (digestive enzymes)
  • aging
29
Q

examples of fuel using control of rxn rates

A
  • conc of O2 is important. to increase combustion rate, you can increase O2 conc OR increase SA, increase temp, add catalyst
  • to decrease combustion rate, water on fire smothers it and decreases O2 and cools it. fire retardant is used on forest fires and children’s clothes. airplane fuels used when spilled
30
Q

examples of industrial processes using control of rxn rates

A
  • all used to produce products quickly
  • fiberglass uses catalyst (hardener) to harden fast
  • epoxy in glue is catalyst
  • concrete, ceramics, paint
  • oil refining
  • sewage treatment uses microbes to speed up breakdown
31
Q

examples of preventing rusting using control of rxn rates

A
  • paint + sealers prevent O2 from contacting surface and keeps surface cool and dry (ex/ cars)
32
Q

examples of control of rxn rates in cooking

A
  • improves taste
  • kills some bacteria
  • if too hot, burning begins as well as production of carcinogens
  • food preservation keeps food at lower temp, uses anti-oxidants (ascorbic acid), keeps out O2 (sealing) and preservatives preserve food too
33
Q

collision theory: 3 requirements for successful collision

A
  • molecules must collide
  • molecules must collide w/sufficient KE, greater than or equal to Ea
  • molecules must collide w/proper collision geometry
34
Q

how collision theory explains the effects of conc on rxn rate

A
  • when both have low conc, low chance of collision so slow rxn
  • when one has high conc, higher chance of collision so faster rxn
  • when both have high conc, very high chance of collision so very fast rxn
35
Q

how collision theory explains effects of temp on rxn rate

A
  • when molecules move faster, more probability of collisions/unit time = faster rate
  • a greater fraction of molecules have sufficient KE so the collisions are effective = faster rate
36
Q

enthalpy

A
  • the heat content of a substance

- total KE + PE of a substance at constant pressure

37
Q

exothermic

A
  • heat is released to surroundings (temp of surroundings gets warmer)
38
Q

endothermic

A
  • heat is absorbed from surroundings (temp of surroundings gets cooler)
39
Q

if the heat term is shown BESIDE the equation…

A
  • if it’s negative, it’s exothermic

- if it’s positive, it’s endothermic

40
Q

thermochemical equations

A
  • heat term is in the equation
  • heat term at left of arrow = endothermic
  • heat term at right of arrow = exothermic
41
Q

when temp is increased, how does this affect molecules?

A
  • average KE increases = fewer slow ones and more fast ones. greater fraction of molecules have KE which is greater/equal to Ea so rxn rate increases
  • curve of molecules is more spread out at higher temp
  • total area under curve is same for high and low temp
42
Q

activation energy

A
  • min KE particles must collide w/to collide successfully
43
Q

if Ea is near tail of curve + temp is increased by 10 degrees C, rxn rate will ___

A
  • approx double
44
Q

if temp is increased + Ea is near middle of curve, rxn rate will ___

A
  • not change much as rxn rate is already fast
45
Q

KE + PE as colliding molecules approach each other

A
  • the repulsion slows them down so KE decreases
  • as they push against repulsive force, PE increases
  • KE + PE = total E (stays constant)
46
Q

progress of rxn in terms of KE and PE

A
  • as molecules approach each other, KE converts to PE
  • molecules form temporary unstable species which exists before products are formed called activated complex
  • AC rearranges to form product molecules
  • product molecules move apart + speed up. PE converts to KE
47
Q

if colliding molecules don’t have enough KE to convert to PE to make it over the activation energy barrier…

A
  • collision is unsuccessful, no rxn. molecules bounce off each other unchanged
48
Q

the Ea is fixed by the ___

A
  • nature of the reactants (#s and strengths of bonds)! to temp or conc or SA of a solid! temp does not change the Ea diagram at all, not the Ea or the change in enthalpy!
49
Q

when collision geometry is unfavourable…

A
  • Ea is very high, so very few molecules will form products
50
Q

how to use PE diagram

A
  • forward rxn: goes from left to right side of graph
  • reverse rxn: goes from right to left side of graph
  • change in enthalpy is change from reactant line to product line
  • Ea(f) js from reactant line to AC line
  • Ea(r) is from product line to AC line
51
Q

most rxns take place in a ___ of simple steps, other than 2 simple particle collisions

A
  • series
52
Q

rxn mechanism

A
  • the series of steps by which a rxn takes place
  • can’t be determined by just looking at overall rxn
  • deduced through much research
  • some mechanisms are known, many are not
  • each step is called an Elementary Process
53
Q

rate determining step

A
  • slowest step in the mechanism
  • overall rxn can never be faster than RDS
  • only way to speed up rxn is by speeding up RDS. speeding up a fast step (not RDS) will have no effect on overall rate
54
Q

rxn intermediate

A
  • species (atom, molecule or ion) which is produced in 1 step + used up in a later step (appears on right + lower left)
  • an intermediate doesn’t accumulate like a product b/c as soon as it’s formed, it gets used up again
  • intermediates aren’t necessarily unstable (they may last a while)
55
Q

PE diagram for rxn mechanism

A
  • each bump is a step
  • the higher the bump, the slower the step
  • the highest bump is the RDS
  • AC’s at top of bumps, intermediates in middle valleys, product in final valley
  • Ea(f) overall vertical distance from reactants to top of highest bump
56
Q

how catalysts work

A
  • produces an alternate mechanism w/lower Ea. more molecules can make it over barrier so rxn rate increases
  • usually involves more steps but its highest Ea is never as high as uncatalyzed rxn
  • catalyst never changes PE/change in enthalpy of reactants/products, only provides alternate route
  • uncatalyzed rxn still continues at its own rate
57
Q

catalysts sometimes work by…

A
  • providing a surface which has atom spacing just right to break reactant molecule + hold it for an attack from another reactant
  • helping to form an intermediate which can react more easily to form products
58
Q

finding catalyst in rxn mechanism

A
  • one that appears on left and later on right side
59
Q

finding AC in rxn mechanism

A
  • for a given step, add up all the junk on the reactant side
60
Q

what 2 phases get affected by concentration changes

A

aqueous and gas

61
Q

the lower the PE is, the _____er the bond is

A
  • strong
62
Q

how would you dissociate CaCl2 (aq)?

A
  • Ca 2+ (aq) +2Cl-(aq)
63
Q

when can you measure pressure if there are no gases in the reactants?

A
  • if it’s a closed system
64
Q

if there are no gases in reactants, will pressure/ volume affect the rxn rate?

A
  • nah bruh

chem 12 (1 decks)

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