AQA Chemistry Definitions Flashcards
Enthalpy change
the heat energy transferred in a reaction at constant pressure
Standard enthalpy of formation
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
Standard enthalpy of combustion
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
Hess’s law
the enthalpy change for a chemical reaction independent of the route taken from reactants to products
Catalyst
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
Enthalpy of atomisation of an element
the enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state
Enthalpy of atomisation of a compound
the enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms
First ionisation energy
the enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms
Second ionisation energy
the enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions
Enthalpy change of hydration
the enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions
Enthalpy change of solution
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
Mean bond enthalpy
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
Bond dissociation enthalpy
the enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken
First electron affinity
the enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms
Second electron affinity
the enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions
Lattice enthalpy of formation
the enthalpy change when 1 mole of solid ionic compound is formed from its gaseous ions under standard conditions
Lattice enthalpy of dissociation
the enthalpy change when 1 mole of solid ionic compound is completely dissociated into its gaseous ions under standard conditions
Used in chromatography for making amino acids visible
Ninhydrin solution or UV light if the TLC plate has fluorescent dye
Rf value
distance travelled by spot/distance travelled by solvent
Primary, secondary and tertiary structures of proteins
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
Name of bond between phosphate group and 2-deoxyribose sugar in DNA
Phosphodiester bond
Halogenoalkanes —> Primary/secondary/tertiary amines/quarternary ammonium salts
Nucleophilic subsitution, requires excess ammonia and heat
Halogenoalkanes —> Nitriles
Nucleophilic substitution, requires KCN dissolved in ethanol, under reflux
Nitriles —> Primary amines
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
Halogenoalkanes —> Alkenes
Base elimination, requires KOH dissolved in ethanol, under reflux
Alkenes —> Halogenoalkanes
Electrophilic addition, HX at room temperature
Halogenoalkanes —> Alcohols
Nucleophilic substitution (hydrolysis), requires warm aqueous NaOH, under reflux
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
Alcohols —> Alkenes
Dehydration; heat with concentrated H2SO4 catalyst, under reflux
Alcohols —> Carboxylic acids
Excess oxidising agent - acidified potassium (VI) dichromate (with dilute acid to acidify) under reflux to fully oxidise
Alcohols —> Aldehyde/ketones
Oxidising agent acidified potassium (VI) dichromate (with dilute acid to acidify) heated in distillation apparatus to prevent further oxidation
Aldehydes —> Carboxylic acids
Excess oxidising agent - acidified potassium (VI) dichromate (with dilute acid to acidify) under reflux to fully oxidise
Aldehydes/ketones —> Alcohols
Use reducing agent NaBH4 (Sodium borohydride) as reagent, dissolved in water with methanol (Nucleophilic addition with H-)
Aldehydes/ketones —> Hydroxynitrile
Nucleophilic addition, with aqueous KCN and H2SO4, room temperature.
Always forms enantiomers with aldehydes
Only does so with ketones if unsymmetrical
Quarternary ammonium salts can be used as:
Cationic surfactants
Acyl chlorides with any nucleophile
Nucleophilic addition-elimination, vigorous/violent reaction, misty white fumes of HCl are always formed (also called acylation)
Acid anhydrides with any nucleophile
Nucleophilic addition-elimination, less vigorous than acyl chlorides, carboxylic acid is always formed (also called acylation)
Carboxylic acids —> esters
Esterification, concentrated sulfuric acid and an alcohol, heated, water always formed (condensation reaction)
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
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)
Esters —> Carboxylate ions + alcohols
Base hydrolysis, dilute sodium hydroxide (NaOH) under reflux
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)
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
Nitrobenzene —> Aromatic amine
Reduction, tin metal and conc. hydrochloric acid under reflux to form salt, then add NaOH solution
Uses for aromatic amines
Perfumes, starting molecules for the production of dyes and pharmaceuticals
Electronegativity
The power of an atom to attract the pair of electrons in a covalent bond
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
Test for ammonium ions
add dilute sodium hydroxide to form ammonia then test using damp red litmus paper - turns blue
Transition metals
a metal that can form one or more stable ions with a partially filled d sub-level
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
alpha amino acid
an amino acid that has its amine group bonded to the same carbon as the carboxyl group
Complex ion
a complex is a central metal atom or ion surrounded by co-ordinately bonded ligands
Ligand
a species that donates a lone pair of electrons to a central transition metal ion to form a co-ordinate bond
Vanadium ion colours
5+ = Yellow 4+ = Blue 3+ = Green 2+ = Violet
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
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
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
Bronsted-Lowry acids and bases
Bronsted-Lowry acid donates H+ ions/protons
Bronsted-Lowry base accept H+ ions/protons
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
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
Relative molecular mass (Mr)
The average mass of a molecule on a scale where an atom of carbon-12 is exactly 12
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.
Biofuel
A fuel that is made from biological material that has recently died
Racemate/Racemic mixture
A solution which contains equal quantities of each enantiomer of an optically active compound
What is used for making aspirin
Aspirin is an ester and so is made by reacting salicylic acid with ethanoic anhydride or ethanoyl chloride
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
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
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
Activation energy
the minimum amount of kinetic energy that particles need to react
What is meant by a strong acid
An acid which completely ionises to give H+ ions in water
Characteristics of dynamic equilibrium
The forward and reverse reactions proceed at equal rates and the concentrations of reactants and products remain constant
Thermal cracking
High temperature (1000 degrees Celsius) and high pressure (70 atm) produces lots of alkenes
Catalytic cracking
Uses Zeolite catalyst, slight pressure and high temperature (450 degrees Celsius) produces aromatic hydrocarbons and motor fuels
