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Chem and Phys > AQA Chemistry Definitions > Flashcards

AQA Chemistry Definitions Flashcards

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1
Q

Enthalpy change

A

the heat energy transferred in a reaction at constant pressure

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2
Q

Standard enthalpy of formation

A

the enthalpy change when 1 mole of a compound is formed from its constituent elements under standard conditions, with all reactants and products in their standard states

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3
Q

Standard enthalpy of combustion

A

the enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions, with all reactants and products in their standard states

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4
Q

Hess’s law

A

the enthalpy change for a chemical reaction independent of the route taken from reactants to products

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5
Q

Catalyst

A

a substance that increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction

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6
Q

Enthalpy of atomisation of an element

A

the enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state

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7
Q

Enthalpy of atomisation of a compound

A

the enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms

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8
Q

First ionisation energy

A

the enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms

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9
Q

Second ionisation energy

A

the enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions

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10
Q

Enthalpy change of hydration

A

the enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions

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11
Q

Enthalpy change of solution

A

the enthalpy change when 1 mole of solute is dissolved in sufficient solvent to form a solution in which the molecules or ions are far enough apart not to interact with each other

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12
Q

Mean bond enthalpy

A

the enthalpy change when 1 mole of gaseous molecules each breaks a covalent bond to form two free radicals, averged over a range of compounds

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13
Q

Bond dissociation enthalpy

A

the enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken

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14
Q

First electron affinity

A

the enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms

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15
Q

Second electron affinity

A

the enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions

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16
Q

Lattice enthalpy of formation

A

the enthalpy change when 1 mole of solid ionic compound is formed from its gaseous ions under standard conditions

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17
Q

Lattice enthalpy of dissociation

A

the enthalpy change when 1 mole of solid ionic compound is completely dissociated into its gaseous ions under standard conditions

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18
Q

Used in chromatography for making amino acids visible

A

Ninhydrin solution or UV light if the TLC plate has fluorescent dye

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19
Q

Rf value

A

distance travelled by spot/distance travelled by solvent

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20
Q

Primary, secondary and tertiary structures of proteins

A

Primary: the polypeptide chain, sequence of amino acids in long chain
Secondary: alpha helix (spiral) or Beta-pleated sheet
Tertiary: chain coils and folds in a characteristic way, with extra bonds between parts of polypeptide chain

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21
Q

Name of bond between phosphate group and 2-deoxyribose sugar in DNA

A

Phosphodiester bond

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22
Q

Halogenoalkanes —> Primary/secondary/tertiary amines/quarternary ammonium salts

A

Nucleophilic subsitution, requires excess ammonia and heat

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23
Q

Halogenoalkanes —> Nitriles

A

Nucleophilic substitution, requires KCN dissolved in ethanol, under reflux

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24
Q

Nitriles —> Primary amines

A

Reduction, LiAlH4 in non-aqueous solvent (like dry ether) followed by dilute acid. Very expensive so alternatively catalytic hydrogenation with hydrogen gas and nickel at high temperature and pressure

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25
Q

Halogenoalkanes —> Alkenes

A

Base elimination, requires KOH dissolved in ethanol, under reflux

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26
Q

Alkenes —> Halogenoalkanes

A

Electrophilic addition, HX at room temperature

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27
Q

Halogenoalkanes —> Alcohols

A

Nucleophilic substitution (hydrolysis), requires warm aqueous NaOH, under reflux

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28
Q

Alkenes —> Alcohols

A

Electrophilic addition with H2SO4 catalyst, then hydrolysis (NS) by adding H2O and warming.
Or Hydration; use steam with a solid phosphoric (V) acid catalyst (H3PO4) at 300 degrees C and pressure of 60 atm

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29
Q

Alcohols —> Alkenes

A

Dehydration; heat with concentrated H2SO4 catalyst, under reflux

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30
Q

Alcohols —> Carboxylic acids

A

Excess oxidising agent - acidified potassium (VI) dichromate (with dilute acid to acidify) under reflux to fully oxidise

31
Q

Alcohols —> Aldehyde/ketones

A

Oxidising agent acidified potassium (VI) dichromate (with dilute acid to acidify) heated in distillation apparatus to prevent further oxidation

32
Q

Aldehydes —> Carboxylic acids

A

Excess oxidising agent - acidified potassium (VI) dichromate (with dilute acid to acidify) under reflux to fully oxidise

33
Q

Aldehydes/ketones —> Alcohols

A

Use reducing agent NaBH4 (Sodium borohydride) as reagent, dissolved in water with methanol (Nucleophilic addition with H-)

34
Q

Aldehydes/ketones —> Hydroxynitrile

A

Nucleophilic addition, with aqueous KCN and H2SO4, room temperature.
Always forms enantiomers with aldehydes
Only does so with ketones if unsymmetrical

35
Q

Quarternary ammonium salts can be used as:

A

Cationic surfactants

36
Q

Acyl chlorides with any nucleophile

A

Nucleophilic addition-elimination, vigorous/violent reaction, misty white fumes of HCl are always formed (also called acylation)

37
Q

Acid anhydrides with any nucleophile

A

Nucleophilic addition-elimination, less vigorous than acyl chlorides, carboxylic acid is always formed (also called acylation)

38
Q

Carboxylic acids —> esters

A

Esterification, concentrated sulfuric acid and an alcohol, heated, water always formed (condensation reaction)

39
Q

What are esters used for

A

Smell so used in perfumes, flavouring.
Polar so can dissolve in polar organic compounds, and low boiling points so evaporate easily from mixtures, making them good solvents in glues and printing inks.
Used as plasticisers - added to plastics during polymerisation to make them more flexible

40
Q

Esters —> Carboxylic acids + alcohols

A

Acid hydrolysis, use water with dilute sufluric acid catalyst, under reflux (lots of water required to shift equilibrium as it is reversible)

41
Q

Esters —> Carboxylate ions + alcohols

A

Base hydrolysis, dilute sodium hydroxide (NaOH) under reflux

42
Q

Benzene —> Phenylketone

A

Electrophilic substitution (Friedel-Crafts Acylation), acyl chloride with AlCl3 catalyst (halogen carrier), heated under reflux with in non-aqueous solvent (like dry ether)

43
Q

Benzene —> Nitrobenzene

A

Electrophilic substitution (Nitration), conc. sulfuric acid and conc. nitric acid to form NO2+ electrophile, keep below 55 degrees celsius to prevent further substitution

44
Q

Nitrobenzene —> Aromatic amine

A

Reduction, tin metal and conc. hydrochloric acid under reflux to form salt, then add NaOH solution

45
Q

Uses for aromatic amines

A

Perfumes, starting molecules for the production of dyes and pharmaceuticals

46
Q

Electronegativity

A

The power of an atom to attract the pair of electrons in a covalent bond

47
Q

Flame test details

A

Dip nichrome wire loop in HCl then unknown compound then hold in clear blue part of bunsen flame
Calcium ions - brick red
Strontium ions - red
Barium ions - pale green

48
Q

Test for ammonium ions

A

add dilute sodium hydroxide to form ammonia then test using damp red litmus paper - turns blue

49
Q

Transition metals

A

a metal that can form one or more stable ions with a partially filled d sub-level

50
Q

Physical and special chemical properties of transition metals

A 
High density, high melting and boiling points, similar ionic radii
Can form complex ions
Form coloured ions 
Good catalysts (due to)
Variable oxidation states
51
Q

alpha amino acid

A

an amino acid that has its amine group bonded to the same carbon as the carboxyl group

52
Q

Complex ion

A

a complex is a central metal atom or ion surrounded by co-ordinately bonded ligands

53
Q

Ligand

A

a species that donates a lone pair of electrons to a central transition metal ion to form a co-ordinate bond

54
Q

Vanadium ion colours

A 
5+ = Yellow
4+ = Blue
3+ = Green
2+ = Violet
55
Q

Catalyst in Contact process

A

Vanadium (V) oxide catalyst (heterogeneous) used to oxidise SO2 to SO3:
V2O5 + SO2 —> V2O4 + SO3

Vanadium (V) oxide then regenerated with oxygen:
V2O4 + 1/2O2 —> V2O5

56
Q

Catalyst in Haber process

A 
Iron catalyst (heterogenous) for making ammonia.
Impurities such as sulfur (come from burning methane to make hydrogen) can poison the iron catalyst by getting adsorbed by it to form iron sulfide
57
Q

Heterogeneous and homogeneous catalysts

A

Heterogeneous - different phase to reactants. Provides active sites located on surface of catalyst. Can be spread over a support medium to make surface area as large as possible
Homogeneous - same physical state as reactants. Works by combining with reactants to form intermediate species which then forms product and re-forms the catalyst

58
Q

Bronsted-Lowry acids and bases

A

Bronsted-Lowry acid donates H+ ions/protons

Bronsted-Lowry base accept H+ ions/protons

59
Q

Relative atomic mass (Ar)

A

The average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12

60
Q

Relative isotopic mass

A

The average mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is exactly 12

61
Q

Relative molecular mass (Mr)

A

The average mass of a molecule on a scale where an atom of carbon-12 is exactly 12

62
Q

Ethanol from fermentation

A

Fermentation is an exothermic reaction carried out by yeast in anaerobic conditions (no oxygen).
Yeast produces enzyme that converts glucose to ethanol and carbon dioxide.
Optimum temperature is 30-40 degrees Celsius.
Once produced, ethanol is separated from mixture by fractional distillation.
Low tech and uses renewable resources.

63
Q

Biofuel

A

A fuel that is made from biological material that has recently died

64
Q

Racemate/Racemic mixture

A

A solution which contains equal quantities of each enantiomer of an optically active compound

65
Q

What is used for making aspirin

A

Aspirin is an ester and so is made by reacting salicylic acid with ethanoic anhydride or ethanoyl chloride

66
Q

Why ethanoic anhydride is used over ethanoyl chloride in industry

A

Ethanoic anhydride is preferred over ethanoyl chloride because:
It is cheaper
It is safer to use as it is less corrosive
Does not react as violently
Does not produce dangerous hydrogen chloride fumes

67
Q

Characteristics of a benzene ring

A

Planar cyclic structure
All C-C bonds are same length, shorter than normal C-C bonds and longer than C=C bonds
Each carbon has a lone pair in a p-orbital that all combine to form a ring of delocalised electrons, making it more stable

68
Q

Le Chatelier’s Principle

A

If a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change

69
Q

Activation energy

A

the minimum amount of kinetic energy that particles need to react

70
Q

What is meant by a strong acid

A

An acid which completely ionises to give H+ ions in water

71
Q

Characteristics of dynamic equilibrium

A

The forward and reverse reactions proceed at equal rates and the concentrations of reactants and products remain constant

72
Q

Thermal cracking

A

High temperature (1000 degrees Celsius) and high pressure (70 atm) produces lots of alkenes

73
Q

Catalytic cracking

A

Uses Zeolite catalyst, slight pressure and high temperature (450 degrees Celsius) produces aromatic hydrocarbons and motor fuels

Chem and Phys (2 decks)

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