DF Flashcards
(151 cards)
1
Q
What is thermochemistry?
A
The study of the energy and heat associated with chemical reactions
2
Q
Fuels can only release energy once _______
A
Combined with oxygen
3
Q
Define exothermic reaction
A
A reaction that gives out energy and heats the surroundings
Has a negative enthalpy change/ ^H
4
Q
Define endothermic reaction
A
A reaction that takes in energy and cools the surroundings
Has a positive enthalpy change/ ^H
5
Q
What is enthalpy change?
A
The quantity of energy transferred in a reaction, shown by ^H and measured in KJmol-1
6
Q
What is an enthalpy diagram?
A
A diagram showing the change in energy from a line representing the reactants to a line representing the products
7
Q
True or false you can measure enthalpy?
A
False, you can only measure the change in enthalpy
8
Q
What is the equation to find the change in enthalpy?
A
^H = H(products) - H(reactants)
^ represents delta (change)
9
Q
What is ‘the system’?
A
The reactants and the products of the reaction that the chemists are interested in
May lose or gain enthalpy as a result of the reaction
10
Q
What does ‘the surroundings’ refer to?
A
The rest of the world that is not concerned on the reaction
11
Q
What are the standard conditions?
A
- specified temperature, (298K, 25°c)
- standard pressure of 1 atm
- standard concentration of 1moldm-3 for solutions
12
Q
Define standard states
A
The physical state of a substance under standard conditions
13
Q
What is Kelvin?
A
Kelvin, K is the SI (international system) unit that could always be used in calculations
0K is known as absolute zero
To convert between kelvin and Celsius +273
14
Q
What is the standard enthalpy change for a reaction?
A
The enthalpy change when molar quantities of reactants as stated in their equation react together under standard conditions
15
Q
By measuring _______ change you can calculate _______ change
A
Temperature, enthalpy
16
Q
What is the equation for energy transferred?
A
Energy transferred,q,J = specific heat capacity, C,Jg-1K-1 x mass,m,g x temp.change,^T,K
17
Q
What is standard enthalpy change of combustion?
A
The enthalpy change that occurs when one mole of a substance is burnt completely in oxygen under standard conditions in standard states
The ^H is always negative
Accurately measured by a bomb calorimeter
18
Q
How do you calculate SEC of combustion in practice?
A
In practice it is often impossible to measure so adjustments are made after to allow for the non-standard conditions
19
Q
What is the standard enthalpy change of formation?
A
The enthalpy change that occurs when one mole of a compound is formed from its constituent elements under the standard conditions in standard states
The SEC of formation of a pure element in its standard state is 0
20
Q
How can SEC of formation be calculated?
A
By making use of known quantities and incorporating these into an enthalpy cycle
21
Q
What is the standard enthalpy change of neutralisation?
A
The enthalpy change when one mole of hydrogen ions react with one mole of hydroxide ions to form one mole of water under standard conditions
22
Q
What equation can be used to show SEC of neutralisation?
A
H+ + OH- —> H2O
23
Q
When writing equations for SEC what must be done?
A
The equation must always be balances to show one mole of the substance reacting, even if this mean halving a mole of oxygen
24
Q
What is an enthalpy cycle?
A
A way of working out an enthalpy change either directly or indirectly
25
What is **Hess’ law**?
States the enthalpy change for any chemical reaction is independent of the intermediate stages, so long as initial and final conditions are the same for each route
26
The total enthalpy change for the indirect route __________ the enthalpy via the direct route
As same as
27
What are more important, reaction profiles or energy level diagrams?
Reaction profiles as they show activation energy
28
Define activation energy
The minimum amount of energy needed to react
29
What is complete combustion?
Occurs when there is a good supply of oxygen, releasing the maximum amount of energy
30
What is incomplete combustion?
Occurs when there is a bad supply of oxygen, less energy is released
31
What problems can incomplete combustion cause?
- carbon monoxide is poisonous
- particular carbon causes respiration problems and global dimming
32
Define Enthalpy, H
The energy content stored in a chemical system
33
1K in temperature change = _ °c
1
34
Energy change is….
Independent of the route taken
35
What can an enthalpy cycle also be called?
- hess’ cycle
- thermochemical cycle
36
How do you calculate the SEC of combustion?
^H1= ^H2-^H3
37
How do you calculate SEC of reaction?
EC reaction = sum of EC products sum of EC reactants
38
What is organic chemistry?
The study of the many carbon compounds found in living organisms
39
What is catenation?
The self linking of atoms of an element to create chains and rings e.g.Carbon
40
Hydrocarbons are…
Compounds containing only hydrogen and carbon
41
What is a benzene ring?
A ring of six carbon atoms and has a ring of delocalised electrons
42
Define aromatic compounds
Compounds that contain one or more benzene rings
43
Define Aliphatic compounds
Compounds that do not contain benzene rings, hydrocarbons with straight or branched chains
44
What is a functional group?
Modifiers that are responsible for the characteristic chemical reactions of molecules
E.g. hydroxyls -OH known as alcohols
45
How reactive are hydrocarbons ?
Relatively Unreactive
46
Describe alkanes
- CnH2n+2
- saturated
- Unreactive
- homologous series
- differs by CH2
47
Define saturated
(Hydrocarbons) containing the maximum number of hydrogen atoms possible
- single bonds only
48
Define homologous series
A series of compounds in which all members have the same general molecular formula
- same functional group
49
What are structural isomers?
Compounds with the same molecular formulae bit different structural formulae
50
What are alkyl groups?
Side chains found on a branched-chain alkane
51
Define systematic name
A name given to one unique chemical substance, out of a specific series or collection
52
What are Cycloalkanes?
Alkane molecules with a cyclic structure, CnC2n
53
What are the IUPAC rules for nomenclature?
The process to name branched alkanes
- find the longest chain
- same side chain using suffix -yl
- name location of side chain using the the number of the attached carbon
- name the compound using location of side chain, side chain, main chain
-list side chains in alphabetical order
54
What are the properties of alkanes?
- boiling point increases with larger molecules
- alkanes mix well with each other
- insoluble in water
55
Define alicyclic compounds
Hydrocarbons where the atoms are joined together in a ring structure
56
Define Energy density
How much energy you can get per kilogram of fuel
57
Define bond enthalpy
The quantity of energy needed to break one mole of bond to give separate atoms all in the gaseous state
- indicates the strength of the bond
- measured using enthalpy cycles
- units in KJmol
58
The __________ the bond length the _________ the bond
Shorter
stronger
59
Explain equilibrium bond length
The atoms move together because of attractive forces but there is repulsive forces between the nuclei
60
Define average bond enthalpies
The average quantity of energy needed to break a particular bond
61
Bond making is …..
Exothermic
62
Bond breaking is…..
Endothermic
63
How can you calculate enthalpy change from bond energies?
Enthalpy change = bonds broken- bonds made
64
Why may a calculated bond enthalpy differ from the ones given in data sheets?
- the calculated enthalpy is not the standard value
-everything must be gaseous so not in standard states
- bond enthalpies are given as averages
65
Define cracking
the breaking down of long-chained saturated hydrocarbons to form a mixture of shorter chained alkanes and alkenes
- any reaction in which a larger molecule is made into a smaller molecule
66
Define unsaturated
any organic compound that has a double bond between carbon atoms
67
What is catalytic cracking?
Cracking done with high heats in the presence of a catalyst
- zeolite is used today at ~45c
68
Define catalyst
a substance which speeds up a reaction but can be recovered chemically unchanged at the end (will regenerate)
69
Define Catalysis
the process of speeding up a chemical reaction using a catalyst
70
What are some features of catalysts?
- may change in the reaction but won't undergo any permanent change
- are only needed in small amounts
- doesn't effect the amount of products or change the enthalpy of the reaction
- will affect the rate of the reaction
71
What is homogenous catalysis?
when the reactants and the catalyst are in the same physical state
- usually gaseous or aqueous
72
What is heterogenous catalysis?
When the catalyst and the reactants are in different physical states
- most commonly solid catalyst (commonly transition metals) with gaseous reactants
73
Explains heterogenous catalysis with a solid catalyst
the reactant will be **adsorbed** onto the surface of the catalyst. this will weaken the bonds in the reactant. as new bonds are made this weakens the bonds between catalyst and reactants so products are released.
74
What is a catalyst poison?
a substance that stoops a catalyst functioning properly
75
How does a catalyst poison work?
the substance adsorbs more strongly than the reactants. this can't be broken down so the active sites on the catalyst surface are now blocked. catalyst is inactive
76
How can an inactive catalyst be regenerated?
Most can't
some can be by reacting off the poison using another reaction
77
What is the Research Octane Number (RON)?
- assigned to fuels according to how well it burns
- the closer to 100 the better the fuel burns
- fuels can be made more effective be adding cyclic and branched alkanes
78
Describe alkenes
- unsaturated hydrocarbons with C=C
- general formula CnH2n
- boiling point increases as number of carbons increase
- when naming the position of the double bond is shown by inserting the number position of the lowest carbon in the double bond between the prefix and suffix
- very reactive
79
What are the two bonds found in a double bond?
sigma and pi
80
Describe a sigma bond
- first bond, is the single bond bond
- the two electrons are arranged between the atoms in an area of increased electron density
- is the overlap of the two s-orbitals
81
Describe a pi bond
- the second bond
- consists of two areas of negative charge
- fixes the carbon atoms in position and prevents rotation of double bond
- is the overlap of two p-orbitals
-the reactive part of the double bond by sideways overlap of p-orbitals
- formed above and below the plane of the bonded atoms
82
Define **electrophile**
a positive ion/delta positive molecule that will be attracted to s negatively charged region and react by accepting a lone pair of electrons to form a covalent bond
83
What is the test for alkenes?
shaking the alkene with bromine water/bromine solution
84
Describe the reaction of ethene with bromine
- bromine becomes polarised as it approaches the alkene
- the delta positive bromine is able to break off and bond to the alkene to create a carbocation
- the other bromine molecule is now able to bond to the carbocation to form dibromoethane
- this is an example of an organic reaction mechanism
85
Define carbocation
an ion with a positively charged carbon atom
86
What is an addition reaction?
a reaction where two or more molecules react to from a single larger molecule
87
The _____________ for a reaction can decide what __________ is used
conditions, mechanism
88
How is ethanol manufactured
via hydration reaction
- at high temperature and high pressure is presence of a catalyst
89
What are the conditions for the manufacturing of ethanol?
gaseous alkene
- high temperatures and pressures
- phosphoric acid catalyst
90
How is ethanol made in the laboratory?
by adding sulfuric acid and then diluting with water
91
What is a hydrogenation reaction?
an addition reaction involving hydrogen that happens on the surface on a catalyst
- alkene to alkane, this is a reduction reaction
92
What is a halogenation reaction?
when a halogen reacts with an alkene to produce a di-substituted haloalkane, happens at room temp
93
What conditions is needed for a hydrogenation reaction of alkene to alkane?
- gaseous alkene
- nickel catalyst
- 150*c
94
Define isomers
molecules with the same molecular formula but different structures
95
Define polymer
a long chain molecule that is made up from lots of small molecule called monomers
- e.g. plastics
96
What is copolymerisation?
when more than one type of monomer is used in addition polymerisation/ the polymerisation process
97
What is polymerisation?
small molecules called monomers join together to produce long chain polymers
98
Define fractional distillation
the separation of the components in a liquid mixture into fractions which differ in boiling point (and hence chemical composition) by means of distillation, typically using a fractionating column
99
What are the benefits of using a catalyst?
- reduces costs
- speeds up the process
- reduces the amount of energy required
- improves percentage yield
- benefits the environment
100
How can we improve petrol/RON?
- Isomerisation
- Reforming
- Cracking
101
What is isomerisation used for?
converting unbranched alkanes into branched alkanes
102
What is reforming used for?
converting aliphatic hydrocarbons into cyclic or aromatic hydrocarbons
103
What is a Z-isomer?
An isomer where the groups are on the same side
104
What is an E-isomer?
An isomer where the groups are on the opposite sides
105
What do chain properties depend on?
- chain length
-tensile strength increases with chain length as long chains are more entangled and have stronger intermolecular bonds
- side groups
-polar groups increase the strength of bonds between polymer chains
- branching
-straight, unbranched chains pack close together so polymer is stronger
- chain flexibility
-the more rigid the chain the stronger the polymer. Hydrocarbons-flexible. Benzene rings-shift
- cross-linking
-more extensive cross-linking makes the polymer harder to melt
- stereoregularity
-the more regular the orientation of the side groups, the closer the packing, the stronger polymer
106
Define tensile strength
The measure of the force needed to break a material
107
Define elasromers
Soft and springy polymers, can be stretched and return to original shape
108
Define plastics
Polymers that are easily molded
109
Define fibres
Polymers which can be made into strong, thin threads
110
Define thermoplastics
Polymers without cross links
Polymer can be deformed, and will set
111
Define thermosets
Polymers with extreme cross-linking
Can’t change shape, eventually will char and burn
112
Define a monomer
A small molecule that combines with many other monomers to form a polymer
113
Define a repeat unit
A specific arrangement of atoms that occurred in a structure over and over again
114
Define addition polymerisation
The process in which unsaturated alkane molecules add in to a growing polymer chain one at a time, to form a very long saturated molecular chain
115
What is avogadros law?
Equal volumes of all gases at the same temperature and pressure contain an equal amount of molecules
1811
116
Define molar volume
The volume occupied by one mole of any gas at a particular temperature and pressure
The volume per mole of gas
117
At room temperature and 1atm what is the molar volume of any gas?
24dm*3*
118
How many cm*3* in 1 dm*3* ?
1000
119
Define isomers
distinct compounds with the same molecular formula but different structural formula
120
what are structural isomers?
isomers where the atoms are bonded together in a different order
121
what are stereoisomers?
isomers where the order f bonding is the same but the arrangement of the atoms in space is different
122
what are the types of structural isomerism?
- chain isomerism, atoms have different arrangements
- position isomerism, functional groups in different positions
- functional grou isomerism, different functional groups, different homologous series
123
what are the types of stereoisomerism?
- E/Z isomerism
- optical isomerism
124
What can E/Z isomerism also be called?
cis/trans isomerism, only applies when both groups on either end of the double bond are the same
125
Why is E/Z isomerism a thing?
the double bond prevents rotation
126
In a Z-isomer are the groups on the same or opposite side?
same, cis
127
In an E-isomer are the groups on the same or opposite side?
opposite side, trans
128
define E/Z isomerism
a type of stereoisomerism in which different groups attacked the each carbon of a carbon C=C double bond may be arranged differently in space because of the restricted rotation of the C=C double bond
129
define cis/trans isomerism
a special type of E/Z isomerism in which there is the same group on both carbons of the C=C double bond
130
List some primary atmosphere pollutants
- particulates
- volatile organic compounds VOC
- carbon monoxide
- carbon dioxide
- nitrogen oxides
- sulfur oxides
131
Wat are the sources of VOCs?
plants, unburnt fuel from petrol engines
132
What is the major polluting effect of particulates?
global dimming, cause lung and heart cancer
133
What is the major polluting effect of VOCs?
photochemical smog
134
What is the major polluting effect of carbon monoxide?
toxic gas, photochemical smog
135
What is the major polluting effect of carbon dioxide?
greenhouse effect
136
What is the major polluting effect of nitrogen oxides?
acid rain, photochemical smog
137
What is the major polluting effect of sulfur oxides?
toxic gas, acid rain
138
describe acid rain
- sulfur dioxide reacts with water to make a weak acid, sulfuric IV acid
- sulfur trioxide reacts with water to make a strong acid, sulfuric VI acid
- nitrgen oxides react with water to form stong nitric acid
- will cause breathing difficulties, corrode limestone, kill forests and life in lakes
139
Describe photochemical smog
formed when primary pollutants are acted upon by sunlight to produce secondary pollutants
- causes haziness, reduced visibility and respiratory problems
140
What is used in a petrol engine?
a three way catalytic converter, consisting of platinum or rhodium on a porous support
141
What are the main pollutants produced in a petrol engine/
CO, hydrocarbons, nitrogen monoxide
NO is reacted with CO to produce N2 and CO2
142
What do diesel engines use?
diesel particulate filters usually containing ceramic. can be regenerated with high temps
143
What are the main pollutants produced by a diesel engine?
CO, hydrocarbons, Particulates and nitrogen oxides
nitrogen oxides can be recycled through the cylinder
144
define biofuels
alternate fuels derived from renewable plant and animal materials
145
what biofuels are there?
- ethanol
- biodiesel
- green diesel
- biogas
146
Describe ethanol
- made by fermentation of carbohydrate crops
- considered carbon neutral
- too volatile to be used alone
147
Describe biodiesel
- made by chemically reacting fats and oils with alcohols to produce fatty acid esters- transesterification
- made using waste oil
- carbon neutral
- biodegradable
- produces less poluutants, more nitrogen oxides
148
What are the advantages of using hydrogen as a fuel?
- renewable, made by water and electrolysis
- stored and sent down pipelines
- produces no pollutants
- used in internal combustion engines or fuel cells
149
What are the disadvantages of using hydrogen as a fuel?
- production of it requires electricity
- less energy dense than petrol
- oxides of nitrogen still formed due to high temps
- needed in large volumes
- needs larger storage
150
describe fuel cells
- used on a small scale in cars
- main product is water
- convert chemical energy from a fuel using a chemical reaction with an oxidising agent (oxygen)
151
