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Chem and Phys > AQA Chemistry Definitions > Flashcards

AQA Chemistry Definitions Flashcards

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
Halogenoalkanes ---> Alkenes
Base elimination, requires KOH dissolved in ethanol, under reflux
26
Alkenes ---> Halogenoalkanes
Electrophilic addition, HX at room temperature
27
Halogenoalkanes ---> Alcohols
Nucleophilic substitution (hydrolysis), requires warm aqueous NaOH, under reflux
28
Alkenes ---> Alcohols
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
29
Alcohols ---> Alkenes
Dehydration; heat with concentrated H2SO4 catalyst, under reflux
30
Alcohols ---> Carboxylic acids
Excess oxidising agent - acidified potassium (VI) dichromate (with dilute acid to acidify) under reflux to fully oxidise
31
Alcohols ---> Aldehyde/ketones
Oxidising agent acidified potassium (VI) dichromate (with dilute acid to acidify) heated in distillation apparatus to prevent further oxidation
32
Aldehydes ---> Carboxylic acids
Excess oxidising agent - acidified potassium (VI) dichromate (with dilute acid to acidify) under reflux to fully oxidise
33
Aldehydes/ketones ---> Alcohols
Use reducing agent NaBH4 (Sodium borohydride) as reagent, dissolved in water with methanol (Nucleophilic addition with H-)
34
Aldehydes/ketones ---> Hydroxynitrile
Nucleophilic addition, with aqueous KCN and H2SO4, room temperature. Always forms enantiomers with aldehydes Only does so with ketones if unsymmetrical
35
Quarternary ammonium salts can be used as:
Cationic surfactants
36
Acyl chlorides with any nucleophile
Nucleophilic addition-elimination, vigorous/violent reaction, misty white fumes of HCl are always formed (also called acylation)
37
Acid anhydrides with any nucleophile
Nucleophilic addition-elimination, less vigorous than acyl chlorides, carboxylic acid is always formed (also called acylation)
38
Carboxylic acids ---> esters
Esterification, concentrated sulfuric acid and an alcohol, heated, water always formed (condensation reaction)
39
What are esters used for
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
Esters ---> Carboxylic acids + alcohols
Acid hydrolysis, use water with dilute sufluric acid catalyst, under reflux (lots of water required to shift equilibrium as it is reversible)
41
Esters ---> Carboxylate ions + alcohols
Base hydrolysis, dilute sodium hydroxide (NaOH) under reflux
42
Benzene ---> Phenylketone
Electrophilic substitution (Friedel-Crafts Acylation), acyl chloride with AlCl3 catalyst (halogen carrier), heated under reflux with in non-aqueous solvent (like dry ether)
43
Benzene ---> Nitrobenzene
Electrophilic substitution (Nitration), conc. sulfuric acid and conc. nitric acid to form NO2+ electrophile, keep below 55 degrees celsius to prevent further substitution
44
Nitrobenzene ---> Aromatic amine
Reduction, tin metal and conc. hydrochloric acid under reflux to form salt, then add NaOH solution
45
Uses for aromatic amines
Perfumes, starting molecules for the production of dyes and pharmaceuticals
46
Electronegativity
The power of an atom to attract the pair of electrons in a covalent bond
47
Flame test details
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
Test for ammonium ions
add dilute sodium hydroxide to form ammonia then test using damp red litmus paper - turns blue
49
Transition metals
a metal that can form one or more stable ions with a partially filled d sub-level
50
Physical and special chemical properties of transition metals
``` 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
alpha amino acid
an amino acid that has its amine group bonded to the same carbon as the carboxyl group
52
Complex ion
a complex is a central metal atom or ion surrounded by co-ordinately bonded ligands
53
Ligand
a species that donates a lone pair of electrons to a central transition metal ion to form a co-ordinate bond
54
Vanadium ion colours
``` 5+ = Yellow 4+ = Blue 3+ = Green 2+ = Violet ```
55
Catalyst in Contact process
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
Catalyst in Haber process
``` 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
Heterogeneous and homogeneous catalysts
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
Bronsted-Lowry acids and bases
Bronsted-Lowry acid donates H+ ions/protons | Bronsted-Lowry base accept H+ ions/protons
59
Relative atomic mass (Ar)
The average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12
60
Relative isotopic mass
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
Relative molecular mass (Mr)
The average mass of a molecule on a scale where an atom of carbon-12 is exactly 12
62
Ethanol from fermentation
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
Biofuel
A fuel that is made from biological material that has recently died
64
Racemate/Racemic mixture
A solution which contains equal quantities of each enantiomer of an optically active compound
65
What is used for making aspirin
Aspirin is an ester and so is made by reacting salicylic acid with ethanoic anhydride or ethanoyl chloride
66
Why ethanoic anhydride is used over ethanoyl chloride in industry
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
Characteristics of a benzene ring
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
Le Chatelier's Principle
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
Activation energy
the minimum amount of kinetic energy that particles need to react
70
What is meant by a strong acid
An acid which completely ionises to give H+ ions in water
71
Characteristics of dynamic equilibrium
The forward and reverse reactions proceed at equal rates and the concentrations of reactants and products remain constant
72
Thermal cracking
High temperature (1000 degrees Celsius) and high pressure (70 atm) produces lots of alkenes
73
Catalytic cracking
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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