rates of reaction Flashcards
1
Q
rate of reaction
A
the change in concentration per unit time of any one reactant or product
2
Q
factors affecting rate
A
nature of reactants particle size concentration temperature catalysts
3
Q
rate graphs
A
concentration inversely proportional to time
temp inversely proportional to time
4
Q
catalyst
A
a substance that alters the rate of reaction but is not consumed in the reaction
5
Q
homogeneous catalysis - when it occurs
A
occurs when reactants + catalyst are in the same phase
6
Q
heterogeneous catalysis - when it occurs
A
occurs when reactants + catalyst are in different phases
7
Q
factors that affect rate of reaction
A
concentration
area (surface area)
temperature
nature of reactants
8
Q
nature of reactants
A
covalent compounds
ionic compounds
9
Q
covalent compounds
A
- slow reactions
- bonds broken before new ones formed
10
Q
ionic compounds
A
- fast reactions
- oppositely charged ions come together
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
12
Q
instantaneous
A
means “at an instant”, not referring to speed of reaction
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
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
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
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
17
Q
types of catalysis
A
homogeneous
heterogeneous
autocatalysis
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
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
20
Q
autocatalysis
A
where one of the products of a reaction catalyses the reaction
eg. reduction of manganate (VII)
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
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
23
Q
carbon monoxide
A
formed from incomplete combustion of hydrocarbons in fuels
- highly toxic in blood stream
- colourless, odourless, tasteless gas
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
25
unburned hydrocarbons
arise from unburned fuel + gives rise to smog
26
catalytic converter
converts environmentally harmful gases into harmless gases
27
what catalytic converter consists of
- 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
28
reactions that take place in catalytic converter
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
29
replacement
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
30
advantage of catalytic converters
- decrease in carbon monoxide emissions, nitrogen oxide emissions, smog, acid rain
- increase in air quality
31
activation energy
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
32
energy profile diagrams
can be used to represent activation energy
bond breaker = endothermic
bond making = exothermic
33
energy in exothermic reaction
more energy released when bonds made than energy taken in to break bonds so overall energy value is negative
34
energy in an endothermic reaction
more energy taken in to break bonds than is released when bonds are made therefore overall energy value positive
35
reaction profiles graphs
in hardback
36
explain effective collision
reaches activation energy
37
inc in temp effect on: no of collisions
increase
38
inc in temp effect on: effectiveness of collisions
increase in effective collisions
39
inc in temp effect on: activation energy
none
40
unit of instantaneous rate
M s⁻¹
41
Suggest a reason why NO is not formed in every collision between a pair of NO2 molecules
molecules did not possess enough energy to break bonds
molecules did not reach activation energy
colliding molecules were not correctly orientated for reaction
42
ways of increasing freq of collisions
- increase temp
- increase concentration (of reactant)
- increase pressure
43
profile diagrams
know profile diagrams
44
describe a method you could use to determine when the same mass of the product had been formed in each run
- 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
concentration vs rate graph + conclusion
straight line through origin
conceptration of x is directly proportional to rate (1/t)
46
how to use same reaction to investigate effect of changing temp on reaction rate
- 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
explain how the type of bonding in the reactants influences the rate of a chemical reaction in aqueous solution
- ionic compounds react quickly (in solution) as dissociated
| - covalent compounds react slowly as bonds need to be broken first before reaction
48
how to reduce rate of a reaction that takes place in solution
- lowering temp (cooling)
- lowering concentration (diluting)
- inhibitor (negative catalyst)
49
oxidation of methanol using platinum wire as catalyst - observation made during experiment
- wire glows and dims
- popping sounds
- flask becomes hot
- flame (flash)
50
oxidation of methanol using platinum wire as catalyst - products of the oxidation
- methanal
- water
- hydrogen
51
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
-lower activation energy
- reactants adsorbed
- more effective collisions
52
term used to describe attachment of liquid or gaseous molecules to a solid surface
adsorption
53
explain how a catalyst poison like sulfur interferes with a catalyst
-surface occupied/blocked by sulfur/poison
/
-sulfur/poison bonded to catalyst
54
graph with reaction rate
reaction rate is 1/time
55
graph of temp vs reaction rate conclusion
rate increases with temperature exponentially
56
why rate increases with temp exponentially
more collisions reach activation energy / more effective collisions
57
what would be the effect on reaction times if experiment repeated using 0.025M sodium thiosulfate instead of 0.05M? justify your answer
- reaction is twice as slows/slower rate
| - rate is directly proportional to concentration/rate decreases with concentration
58
metals used as catalysts in catalytic converters
- platinum
- palladium
- rhodium
59
-type of catalysis occurs in catalytic converts fitted to car exhausts
heterogeneous / surface adsorption
60
ways catalysts increase rate of reaction
- lower activation energy
- reactants brought closer on surface
- reactants adsorbed on surface
61
substance that could poison the catalysts of the catalytic converter
- lead compounds
| - sulfur compounds
62
unit for instantaneous rate
depends on graph
it will be unit of y-axis/unit of x-axis n
63
why there is an almost instantaneous reaction between aqueous solutions of sodium chloride and silver nitrate
they are ionic compounds / ions free in solution
64
ways to increase rate of a reaction + how they do so
- 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
how to measure reaction time of a reaction (experiment)
- 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
describe how you would show reaction rate is directly proportional to the concentration of a solution
- 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
how temp, conc, catalyst affects graphs
know how to draw (on book)
68
effect on graph of decreasing the concentration
- 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
describe mechanism by which a catalyst increases the rate of reaction
- reactants adsorbed on surface of catalyst
- forming activated complex
- lowering activation energy
70
primary metabolite of ethanol in the human liver
ethanal (acetaldehyde)
71
increase in temp on:
1) number of collisions
2) effectiveness of the collisions
3) the activation energy
1) small increase
2) large increase in effective collisions
3) no effect / none
72
oxidation of methanol using platinum wire as catalyst -type of catalysis involved in this reaction
heterogenous
73
oxidation of methanol using platinum wire as catalyst -how a catalyst poison interferes with this type of catalysis
preferentially adsorbed on catalyst
74
another example of a reaction which involes the same type of catalysis
```
Hydrogen peroxide and Manganese (IV)oxide
/
Ethanol and Aluminium oxide
/
Ethanol and Platinum
/
Hydrogen + Oxygen and Platinum
```
75
why does the rate of chemical reactions generally decrease with time
concentrations decrease (Reactants used up)
76
instantaneous rate unit
depends on graph
eg g/min or g/sec
77
effect of decreasing diameter range of the chips used in reaction experiment
-steeper at start, levels off sooner, reaches same height
78
conditions for a dust explosion
- combustible dust particles
- dryness
- source of ignition (light, spark, flame, static electricity)
- enclosed space
79
reasons why rate of chemical reaction increases as temp increases and which is more significant
1) increased energy of ollisions
2) increased number of collisions
-first reason
80
how you could investigate effect of temp on rate of a reaction between two solutions
- 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
explain speed of reaction between sodium chloride and silver nitrate solutions compared to reaction between covalent molecules
AgNO3 and NaCl are present as free ions in solution
However for x and y, covalent bonds must be broken
82
type of catalysis in catalytic converter
heterogeneous catalysis
83
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
- 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
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
- 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
describe how you would demonstrate the effects of particle size on rate
- mass of small particles equal mass of larger particles
- added to equal volumes of HCl of same conc
- note times to complete reactions
86
unit of rate
s⁻¹
87
when plotting rate vs x
get rate if only time is given, ie get 1/time
88
"use your graph (reaction rate vs temp) to find the reaction time at 35 degrees celsius"
be careful!!!!!!!!, find reaction time not just reaction rate
- Find reaction rate on graph
- Turn into reaction time using 1/time
89
"draw a reaction profile diagram of the reaction with and without a catalyst"
draw both profiles on the same graph
90
when plotting a graph of x vs reaction rate
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
"would you expect reaction times to increase, decrease, or stay the same if you increased the temp?"
decrease, because reaction rate increases with temp
92
decomposition of hydrogen peroxide equation
H2O2 --> H2O + 1/2O2
93
why graph steepest at beginning (graph of reaction time vs volume)
greatest rate, higest conc, most collisions
94
describe how to investigate effect of temp on reaction rate
- 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
change on graph of time vs volume if concentration was halved
-rise less steep
-half the final volume
-
96
why reciprocal of time (1/time) used as rate
rate and time inversely related
rate proportional 1/t
97
proceedure for preparing 0.08M soln from 0.1M solution
- use burette to measure 80 cm3 of 0.1M soln
- make up with di water
- to 100cm3
