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LC Chemistry > rates of reaction > Flashcards

rates of reaction Flashcards

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1
Q

rate of reaction

A

the change in concentration per unit time of any one reactant or product

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2
Q

factors affecting rate

A 
nature of reactants
particle size
concentration
temperature
catalysts
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3
Q

rate graphs

A

concentration inversely proportional to time

temp inversely proportional to time

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4
Q

catalyst

A

a substance that alters the rate of reaction but is not consumed in the reaction

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5
Q

homogeneous catalysis - when it occurs

A

occurs when reactants + catalyst are in the same phase

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6
Q

heterogeneous catalysis - when it occurs

A

occurs when reactants + catalyst are in different phases

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7
Q

factors that affect rate of reaction

A

concentration
area (surface area)
temperature
nature of reactants

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8
Q

nature of reactants

A

covalent compounds

ionic compounds

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9
Q

covalent compounds

A
  • slow reactions

- bonds broken before new ones formed

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10
Q

ionic compounds

A
  • fast reactions

- oppositely charged ions come together

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11
Q

general rules for graphs

A
  • use graph paper
  • label both axis with title and units
  • plot points accurately
  • if two things to plot on graph, put both on same graph if they tell you to. Draw in diff colours and write a key outside
  • decrease in graphs has -y axis
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12
Q

instantaneous

A

means “at an instant”, not referring to speed of reaction

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13
Q

temperature

A
  • the hotter the temp, the more energy the particles have
  • more energy - faster the particles move
  • more effective + frequent collisions + reaction occurs quicker
  • higher the temp, shorter the reaction time
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14
Q

concentration

A
  • increasing concentration, increases rate of reaction
  • for H₂O₂ - inc conc, inc amount of product (gas) produced, as it is the only reactant present
  • for hydrochloric acid + sodium thiosulphate - inc conc, causes same amount of gas to be produced but in shorter time
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15
Q

eg of catalyst

A

hydrogen peroxide decomposes into water + oxygen at room temp, the addition of manganese dioxide as a catalyst causes hydrogen peroxide to decompose faster

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16
Q

properties of catalyst

A
  • remains chemically unchanged at end of reaction
  • only needed in small amounts
  • specific - work for one reaction but not another
  • in equilibrium reactions - a catalyst helps equilibrium to be achieved quicker
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17
Q

types of catalysis

A

homogeneous
heterogeneous
autocatalysis

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18
Q

homogeneous catalysis

A

both reactants + catalyst are in same physical state
no boundary between reactants + catalyst

eg. both are liquids - aqueous potassium iodide + hydrogen peroxide, potassium iodide breaks H₂O₂ into water and oxygen

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19
Q

heterogeneous catalysis

A

reactants + catalyst are in diff physical state
there is a boundary between reactants + catalyst

eg. hydrogen peroxide (liquid) + manganese dioxide (solid) or oxidation of methanol by platinum catalyst

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20
Q

autocatalysis

A

where one of the products of a reaction catalyses the reaction

eg. reduction of manganate (VII)

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21
Q

reduction of manganate (vii)

A

MnO₄⁻ + 8H⁺ + 5Fe²⁺ –> Mn²⁺ + 5Fe³⁺ + 4H₂O

Mn²⁺ catalyses the reaction
purple colour decolorises slowly
decolorising speeds up due to Mn²⁺ ions produced, catalysing reaction

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22
Q

catalytic converters

A

exhaust fumes are a major source of air pollution. They can release these in the atmosphere:

  • Carbon monoxide (CO)
  • nitrogen monoxide (NO)
  • Nitrogen dioxide (NO₂)
  • unburned hydrocarbons
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23
Q

carbon monoxide

A

formed from incomplete combustion of hydrocarbons in fuels

  • highly toxic in blood stream
  • colourless, odourless, tasteless gas
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24
Q

nitrogen oxide

A

formed when atmospheric nitrogen and oxygen react at high temp of spark plug

  • then reacts w/ more oxygen to form nitrogen dioxide
  • nitrogen dioxide reacts w/ water to form nitric acid, leads to acid rain
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25
Q

unburned hydrocarbons

A

arise from unburned fuel + gives rise to smog

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26
Q

catalytic converter

A

converts environmentally harmful gases into harmless gases

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27
Q

what catalytic converter consists of

A
  • thin coating of platinum, palladium, thiodium on ceramic/metal honeycomb inside stainless steel case
  • catalysts spread over surface of honeycomb which has large surface area
  • mixture of hot harmful gases then converted into harmless products
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28
Q

reactions that take place in catalytic converter

A

2CO + 2NO –(Pt/Pd/Rh)–> 2CO₂ + N₂

unburned hydrocarbons react with oxides of nitrogen to form carbon dioxide, nitrogen + water which occur naturally in the air

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29
Q

replacement

A

catalytic converters will need to be replaced due to poisoning of catalyst mainly from lead. When the converter is changed it is possible to recover most of the catalyst + recycle it

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30
Q

advantage of catalytic converters

A
  • decrease in carbon monoxide emissions, nitrogen oxide emissions, smog, acid rain
  • increase in air quality
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31
Q

activation energy

A

minimum energy which colliding particles must have for a reaction to occur (between them)

  • chemical reactions involve formation of bonds between atoms, but often before new bonds can be formed old ones have to be broken
  • there has to be enough energy to start breaking old bonds before reaction can occur
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32
Q

energy profile diagrams

A

can be used to represent activation energy

bond breaker = endothermic
bond making = exothermic

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33
Q

energy in exothermic reaction

A

more energy released when bonds made than energy taken in to break bonds so overall energy value is negative

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34
Q

energy in an endothermic reaction

A

more energy taken in to break bonds than is released when bonds are made therefore overall energy value positive

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35
Q

reaction profiles graphs

A

in hardback

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36
Q

explain effective collision

A

reaches activation energy

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37
Q

inc in temp effect on: no of collisions

A

increase

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38
Q

inc in temp effect on: effectiveness of collisions

A

increase in effective collisions

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39
Q

inc in temp effect on: activation energy

A

none

40
Q

unit of instantaneous rate

A

M s⁻¹

41
Q

Suggest a reason why NO is not formed in every collision between a pair of NO2 molecules

A

molecules did not possess enough energy to break bonds

molecules did not reach activation energy

colliding molecules were not correctly orientated for reaction

42
Q

ways of increasing freq of collisions

A
  • increase temp
  • increase concentration (of reactant)
  • increase pressure
43
Q

profile diagrams

A

know profile diagrams

44
Q

describe a method you could use to determine when the same mass of the product had been formed in each run

A
  • cross print under flask

- obscured/no longer visible when viewed through same depth of solution in each run using identical flask in each run

45
Q

concentration vs rate graph + conclusion

A

straight line through origin

conceptration of x is directly proportional to rate (1/t)

46
Q

how to use same reaction to investigate effect of changing temp on reaction rate

A
  • repeat using water bath/heating solutions using hotplate (bunsen burner)
  • at a number of diff temperatures
  • with fixed volumes and concentrations of x and y (Reactants)
  • repeat a specified run from examination question eg repeat Run r
  • record reaction times and plot graph of temp vs reaction rates (inverse times)
47
Q

explain how the type of bonding in the reactants influences the rate of a chemical reaction in aqueous solution

A
  • ionic compounds react quickly (in solution) as dissociated

- covalent compounds react slowly as bonds need to be broken first before reaction

48
Q

how to reduce rate of a reaction that takes place in solution

A
  • lowering temp (cooling)
  • lowering concentration (diluting)
  • inhibitor (negative catalyst)
49
Q

oxidation of methanol using platinum wire as catalyst - observation made during experiment

A
  • wire glows and dims
  • popping sounds
  • flask becomes hot
  • flame (flash)
50
Q

oxidation of methanol using platinum wire as catalyst - products of the oxidation

A
  • methanal
  • water
  • hydrogen
51
Q

oxidation of methanol using platinum wire as catalyst - explain how this type of interaction between the methanol and platinum catalyst affects the rate of oxidation

A

-lower activation energy

  • reactants adsorbed
  • more effective collisions
52
Q

term used to describe attachment of liquid or gaseous molecules to a solid surface

A

adsorption

53
Q

explain how a catalyst poison like sulfur interferes with a catalyst

A

-surface occupied/blocked by sulfur/poison
/
-sulfur/poison bonded to catalyst

54
Q

graph with reaction rate

A

reaction rate is 1/time

55
Q

graph of temp vs reaction rate conclusion

A

rate increases with temperature exponentially

56
Q

why rate increases with temp exponentially

A

more collisions reach activation energy / more effective collisions

57
Q

what would be the effect on reaction times if experiment repeated using 0.025M sodium thiosulfate instead of 0.05M? justify your answer

A
  • reaction is twice as slows/slower rate

- rate is directly proportional to concentration/rate decreases with concentration

58
Q

metals used as catalysts in catalytic converters

A
  • platinum
  • palladium
  • rhodium
59
Q

-type of catalysis occurs in catalytic converts fitted to car exhausts

A

heterogeneous / surface adsorption

60
Q

ways catalysts increase rate of reaction

A
  • lower activation energy
  • reactants brought closer on surface
  • reactants adsorbed on surface
61
Q

substance that could poison the catalysts of the catalytic converter

A
  • lead compounds

- sulfur compounds

62
Q

unit for instantaneous rate

A

depends on graph

it will be unit of y-axis/unit of x-axis n

63
Q

why there is an almost instantaneous reaction between aqueous solutions of sodium chloride and silver nitrate

A

they are ionic compounds / ions free in solution

64
Q

ways to increase rate of a reaction + how they do so

A
  • increased pressure: closer molecules means more collisions per unit time
  • increased temperature: more collisions reach activation energy/more effective collisions
  • addition of a catalyst: lowers activation energy/more effective collisions
65
Q

how to measure reaction time of a reaction (experiment)

A
  • place x solutions in a vessel over a cross on a white surface
  • add the y solution and start a stopwatch
  • note the time when the cross becomes invisible when viewed through the solution
66
Q

describe how you would show reaction rate is directly proportional to the concentration of a solution

A
  • place x solutions in a vessel over a cross on a white surface
  • add the y solution and start a stopwatch
  • note the time when the cross becomes invisible when viewed through the solution
  • repeat for each of the given solutions
  • find the reciprocals of the times/find te 1/t values to get the rates
  • plot of rate against conc gives a straight line through the origin (0,0)
67
Q

how temp, conc, catalyst affects graphs

A

know how to draw (on book)

68
Q

effect on graph of decreasing the concentration

A
  • less steep at start due to lower conc of HCl
  • rises to half the height due to HCl concentration being halved
  • levels of later as reaction slower due to lower conc of HCl
69
Q

describe mechanism by which a catalyst increases the rate of reaction

A
  • reactants adsorbed on surface of catalyst
  • forming activated complex
  • lowering activation energy
70
Q

primary metabolite of ethanol in the human liver

A

ethanal (acetaldehyde)

71
Q

increase in temp on:

1) number of collisions
2) effectiveness of the collisions
3) the activation energy

A

1) small increase
2) large increase in effective collisions
3) no effect / none

72
Q

oxidation of methanol using platinum wire as catalyst -type of catalysis involved in this reaction

A

heterogenous

73
Q

oxidation of methanol using platinum wire as catalyst -how a catalyst poison interferes with this type of catalysis

A

preferentially adsorbed on catalyst

74
Q

another example of a reaction which involes the same type of catalysis

A 
Hydrogen peroxide and Manganese (IV)oxide
/
Ethanol and Aluminium oxide
/
Ethanol and Platinum
/
Hydrogen + Oxygen and Platinum
75
Q

why does the rate of chemical reactions generally decrease with time

A

concentrations decrease (Reactants used up)

76
Q

instantaneous rate unit

A

depends on graph

eg g/min or g/sec

77
Q

effect of decreasing diameter range of the chips used in reaction experiment

A

-steeper at start, levels off sooner, reaches same height

78
Q

conditions for a dust explosion

A
  • combustible dust particles
  • dryness
  • source of ignition (light, spark, flame, static electricity)
  • enclosed space
79
Q

reasons why rate of chemical reaction increases as temp increases and which is more significant

A

1) increased energy of ollisions
2) increased number of collisions

-first reason

80
Q

how you could investigate effect of temp on rate of a reaction between two solutions

A
  • heat known volumes of the solutions separately to a certain temp
  • mix, note temperature, and place reaction vessel over cross on …., keeping at temperature
  • record time for cross to become invisible and take rate as 1/time
  • repeat for other temps
81
Q

explain speed of reaction between sodium chloride and silver nitrate solutions compared to reaction between covalent molecules

A

AgNO3 and NaCl are present as free ions in solution

However for x and y, covalent bonds must be broken

82
Q

type of catalysis in catalytic converter

A

heterogeneous catalysis

83
Q

substances entering a car’s catalytic converter and substances to which they are converted in the interior of the catalytic converter + environmental benefit of this process

A
  • carbon monoxide (CO) to carbon dioxide (CO2) - CO toxic
  • Hydrocarbon/named hydrocarbon to carbon dioxide and water - prevents smog/reduces greenhouse effect
  • CO and NO to CO2 and nitrogen - CO toxic/NO leads to acid rain
84
Q

The oxidation of potassium sodium tartrate by hydrogen peroxide catalysted by cobalt(II) ions provides evidence for the intermediate formation theory of catalysis. State observations during epxeriment

+ how these provide evidence for intermediate formation theory

A
  • pink at start of reaction
  • then bubbling as reaction mixture turns green
  • reaction finishes and mixture turns pink again
  • colour change from pink to green indicates formation of new substance
  • change back to original colour (pink) suggests it is an intermediate
  • bubbling while green suggests intermediate is reacting
85
Q

describe how you would demonstrate the effects of particle size on rate

A
  • mass of small particles equal mass of larger particles
  • added to equal volumes of HCl of same conc
  • note times to complete reactions
86
Q

unit of rate

A

s⁻¹

87
Q

when plotting rate vs x

A

get rate if only time is given, ie get 1/time

88
Q

“use your graph (reaction rate vs temp) to find the reaction time at 35 degrees celsius”

A

be careful!!!!!!!!, find reaction time not just reaction rate

  • Find reaction rate on graph
  • Turn into reaction time using 1/time
89
Q

“draw a reaction profile diagram of the reaction with and without a catalyst”

A

draw both profiles on the same graph

90
Q

when plotting a graph of x vs reaction rate

A

if values are given in min, use min on the graph don’t label graph as s, if you use s, then dont forget to convert from min to s

91
Q

“would you expect reaction times to increase, decrease, or stay the same if you increased the temp?”

A

decrease, because reaction rate increases with temp

92
Q

decomposition of hydrogen peroxide equation

A

H2O2 –> H2O + 1/2O2

93
Q

why graph steepest at beginning (graph of reaction time vs volume)

A

greatest rate, higest conc, most collisions

94
Q

describe how to investigate effect of temp on reaction rate

A
  • heat known volumes of the solutions separately to certain temp
  • mix, note temp, place reaction vessel over cross , keeping it at the temp
  • record time taken for cross to become invisible
  • take rate as 1/time
  • repeat for diff temps
95
Q

change on graph of time vs volume if concentration was halved

A

-rise less steep
-half the final volume
-

96
Q

why reciprocal of time (1/time) used as rate

A

rate and time inversely related

rate proportional 1/t

97
Q

proceedure for preparing 0.08M soln from 0.1M solution

A
  • use burette to measure 80 cm3 of 0.1M soln
  • make up with di water
  • to 100cm3

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