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DF Flashcards

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1
Q

What is thermochemistry?

A

The study of the energy and heat associated with chemical reactions

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2
Q

Fuels can only release energy once _______

A

Combined with oxygen

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3
Q

Define exothermic reaction

A

A reaction that gives out energy and heats the surroundings
Has a negative enthalpy change/ ^H

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4
Q

Define endothermic reaction

A

A reaction that takes in energy and cools the surroundings
Has a positive enthalpy change/ ^H

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5
Q

What is enthalpy change?

A

The quantity of energy transferred in a reaction, shown by ^H and measured in KJmol-1

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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

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7
Q

True or false you can measure enthalpy?

A

False, you can only measure the change in enthalpy

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8
Q

What is the equation to find the change in enthalpy?

A

^H = H(products) - H(reactants)
^ represents delta (change)

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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

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10
Q

What does ‘the surroundings’ refer to?

A

The rest of the world that is not concerned on the reaction

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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
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12
Q

Define standard states

A

The physical state of a substance under standard conditions

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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

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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

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15
Q

By measuring _______ change you can calculate _______ change

A

Temperature, enthalpy

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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

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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

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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

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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

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20
Q

How can SEC of formation be calculated?

A

By making use of known quantities and incorporating these into an enthalpy cycle

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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

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22
Q

What equation can be used to show SEC of neutralisation?

A

H+ + OH- —> H2O

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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

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24
Q

What is an enthalpy cycle?

A

A way of working out an enthalpy change either directly or indirectly

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25
Q

What is Hess’ law?

A

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

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26
Q

The total enthalpy change for the indirect route __________ the enthalpy via the direct route

A

As same as

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27
Q

What are more important, reaction profiles or energy level diagrams?

A

Reaction profiles as they show activation energy

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28
Q

Define activation energy

A

The minimum amount of energy needed to react

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29
Q

What is complete combustion?

A

Occurs when there is a good supply of oxygen, releasing the maximum amount of energy

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30
Q

What is incomplete combustion?

A

Occurs when there is a bad supply of oxygen, less energy is released

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31
Q

What problems can incomplete combustion cause?

A
  • carbon monoxide is poisonous
  • particular carbon causes respiration problems and global dimming
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32
Q

Define Enthalpy, H

A

The energy content stored in a chemical system

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33
Q

1K in temperature change = _ °c

A

1

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34
Q

Energy change is….

A

Independent of the route taken

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35
Q

What can an enthalpy cycle also be called?

A
  • hess’ cycle
  • thermochemical cycle
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36
Q

How do you calculate the SEC of combustion?

A

^H1= ^H2-^H3

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37
Q

How do you calculate SEC of reaction?

A

EC reaction = sum of EC products sum of EC reactants

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38
Q

What is organic chemistry?

A

The study of the many carbon compounds found in living organisms

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39
Q

What is catenation?

A

The self linking of atoms of an element to create chains and rings e.g.Carbon

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40
Q

Hydrocarbons are…

A

Compounds containing only hydrogen and carbon

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41
Q

What is a benzene ring?

A

A ring of six carbon atoms and has a ring of delocalised electrons

42
Q

Define aromatic compounds

A

Compounds that contain one or more benzene rings

43
Q

Define Aliphatic compounds

A

Compounds that do not contain benzene rings, hydrocarbons with straight or branched chains

44
Q

What is a functional group?

A

Modifiers that are responsible for the characteristic chemical reactions of molecules
E.g. hydroxyls -OH known as alcohols

45
Q

How reactive are hydrocarbons ?

A

Relatively Unreactive

46
Q

Describe alkanes

A
  • CnH2n+2
  • saturated
  • Unreactive
  • homologous series
  • differs by CH2
47
Q

Define saturated

A

(Hydrocarbons) containing the maximum number of hydrogen atoms possible
- single bonds only

48
Q

Define homologous series

A

A series of compounds in which all members have the same general molecular formula
- same functional group

49
Q

What are structural isomers?

A

Compounds with the same molecular formulae bit different structural formulae

50
Q

What are alkyl groups?

A

Side chains found on a branched-chain alkane

51
Q

Define systematic name

A

A name given to one unique chemical substance, out of a specific series or collection

52
Q

What are Cycloalkanes?

A

Alkane molecules with a cyclic structure, CnC2n

53
Q

What are the IUPAC rules for nomenclature?

A

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
Q

What are the properties of alkanes?

A
  • boiling point increases with larger molecules
  • alkanes mix well with each other
  • insoluble in water
55
Q

Define alicyclic compounds

A

Hydrocarbons where the atoms are joined together in a ring structure

56
Q

Define Energy density

A

How much energy you can get per kilogram of fuel

57
Q

Define bond enthalpy

A

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
Q

The __________ the bond length the _________ the bond

A

Shorter
stronger

59
Q

Explain equilibrium bond length

A

The atoms move together because of attractive forces but there is repulsive forces between the nuclei

60
Q

Define average bond enthalpies

A

The average quantity of energy needed to break a particular bond

61
Q

Bond making is …..

A

Exothermic

62
Q

Bond breaking is…..

A

Endothermic

63
Q

How can you calculate enthalpy change from bond energies?

A

Enthalpy change = bonds broken- bonds made

64
Q

Why may a calculated bond enthalpy differ from the ones given in data sheets?

A
  • the calculated enthalpy is not the standard value
    -everything must be gaseous so not in standard states
  • bond enthalpies are given as averages
65
Q

Define cracking

A

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
Q

Define unsaturated

A

any organic compound that has a double bond between carbon atoms

67
Q

What is catalytic cracking?

A

Cracking done with high heats in the presence of a catalyst
- zeolite is used today at ~45c

68
Q

Define catalyst

A

a substance which speeds up a reaction but can be recovered chemically unchanged at the end (will regenerate)

69
Q

Define Catalysis

A

the process of speeding up a chemical reaction using a catalyst

70
Q

What are some features of catalysts?

A
  • 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
Q

What is homogenous catalysis?

A

when the reactants and the catalyst are in the same physical state
- usually gaseous or aqueous

72
Q

What is heterogenous catalysis?

A

When the catalyst and the reactants are in different physical states
- most commonly solid catalyst (commonly transition metals) with gaseous reactants

73
Q

Explains heterogenous catalysis with a solid catalyst

A

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
Q

What is a catalyst poison?

A

a substance that stoops a catalyst functioning properly

75
Q

How does a catalyst poison work?

A

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
Q

How can an inactive catalyst be regenerated?

A

Most can’t
some can be by reacting off the poison using another reaction

77
Q

What is the Research Octane Number (RON)?

A
  • 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
Q

Describe alkenes

A
  • 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
Q

What are the two bonds found in a double bond?

A

sigma and pi

80
Q

Describe a sigma bond

A
  • 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
Q

Describe a pi bond

A
  • 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
Q

Define electrophile

A

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
Q

What is the test for alkenes?

A

shaking the alkene with bromine water/bromine solution

84
Q

Describe the reaction of ethene with bromine

A
  • 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
Q

Define carbocation

A

an ion with a positively charged carbon atom

86
Q

What is an addition reaction?

A

a reaction where two or more molecules react to from a single larger molecule

87
Q

The _____________ for a reaction can decide what __________ is used

A

conditions, mechanism

88
Q

How is ethanol manufactured

A

via hydration reaction
- at high temperature and high pressure is presence of a catalyst

89
Q

How is ethanol made in the laboratory?

A

by adding sulfuric acid and then diluting with water

90
Q

What is a hydrogenation reaction?

A

an addition reaction involving hydrogen that happens on the surface on a catalyst
- alkene to alkane

91
Q

Define isomers

A

molecules with the same molecular formula but different structures

92
Q

Define polymer

A

a long chain molecule that is made up from lots of small molecule called monomers
- e.g. plastics

93
Q

What is copolymerisation?

A

when more than one type of monomer is used in addition polymerisation/ the polymerisation process

94
Q

What is polymerisation?

A

small molecules called monomers join together to produce long chain polymers

95
Q

Define fractional distillation

A

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

96
Q

What are the benefits of using a catalyst?

A
  • reduces costs
  • speeds up the process
  • reduces the amount of energy required
  • improves percentage yield
  • benefits the environment
97
Q

How can we improve petrol/RON?

A
  • Isomerisation
  • Reforming
  • Cracking
98
Q

What is isomerisation used for?

A

converting unbranched alkanes into branched alkanes

99
Q

What is reforming used for?

A

converting aliphatic hydrocarbons into cyclic or aromatic hydrocarbons

100
Q

What is a Z-isomer?

A

An isomer where the groups are on the same side

101
Q

What is an E-isomer?

A

An isomer where the groups are on the opposite sides

Chemistry (4 decks)

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