Definitions Flashcards
activated complex
an unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction
activation energy
the energy required by colliding molecules to form an activated complex
addition reaction
a reaction in which two or more molecules combine to produce a larger molecule and nothing else
alcohols
carbon compounds which contain the hydroxyl -OH functional group
aldehydes
carbon compounds which contain the -C=O functional group. they are formed by oxidation of primary alcohols and oxidise to produce carboxylic acids.
alkanes
a homologous series of saturated hydrocarbons, general formula CnH2n+2. first member is methane CH4
alkenes
a homologous series of unsaturated hydrocarbons, general formula CnH2n. each member contains a carbon to carbon double bond. first member is ethene. CH2=CH2
alkyl group
a group of carbon and hydrogen atoms forming a branch in a carbon compound, for example methyl group (CH3-) or ethyl group (C2H5-)
amide link
a group of atoms formed by condensation polymerisation of amino acids in the formation of protein chains. the amide link is CONH and occurs between each pair of amino acid residues in the chain. also called a peptide link
amine group
a functional group -NH2
amino acids
compounds of general formula, H2NCHRCOOH where R is a difference which link by condensation reaction to form proteins.
essential amino acids
cannot be synthesised by an organism and must be present in its diet
antioxidants
compounds that slow oxidation reactions. they are commonly added to food to prevent edible oils becoming rancid. example include vitamin E and C
atom economy
a measure of the proportion of reactants that have been converted into products. it is calculated using formula, atom economy = mass of desired product/total mass of reactants x 100. reactions with a high atom economy are desirable
atomic number
numbers of protons in the nucleus of an atom
average rate
the change in mass or conc. of a reactant or product divided by time interval during which the change occurs
biodegrade
the breakdown of materials by bacteria or other biological means
bonding continuum
a concept applied to bonding. ionic and covalent bonding lie at opposite ends with polar covalent bonding in-between on the continuum
carbonyl group
C=O. it is present in ketones and aldehydes
catalyst
a substance which speeds up a reaction without itself being used up by providing an alternative pathway and it lowers the activation energy
chromatography
a technique used for separating substances. molecules of different size or polarity can be separated by this technique which used a mobile phase of gas or liquid passing over a stationary phase of solid or liquid-impregnated solid
closed system
reversible reactions will only reach a state of dynamic equilibrium when the reaction takes place in a reaction vessel which prevents reactants and products escaping
collision theory
a theory used to explain the factors which lead to a successful collision. they require reactants to i) collide, ii) have correct collision geometry and iii) have sufficient activation energy before a reaction occurs
condensation polymerisation
a process whereby many small molecules (monomers) join to form a large molecule (polymer) with water or other small molecules formed at the same time. an example of this is forming a protein form amino acids
condensation reaction
a reaction in which two (or more) molecules join together by the elimination of a small molecules, such as water
covalent bonding
a bond formed between two atoms by the sharing of a pair of electrons. this usually occurs between non-metal atoms
covalent molecular
bonding in various non-metal small molecules like water or chlorine (Cl2)
covalent network
a very strong stable structure held together by strong covalent bonds. consequently, the compounds are all solids at room temperature and have very high melting points
covalent radius
a useful measure of atomic size, being half the distance between the nuclei of two covalently bonded atoms of an element. covalent bond lengths between any two atoms can be obtained by adding the appropriate covalent bond radii.
cycloalkanes
a homologous series of saturated ring molecules with general formula CnH2n. simplest is cyclopropane, C3H6
dehydration
the removal of water from a single compound for example dehydration of ethanol C2H5OH produces ethene C2H4.
denaturing/denature
altering the shape of a protein by an increase in temperature or a reduction in pH. loss of enzyme activity is a consequence
detergent `
a soap-like molecule which can dissolve fats and oils. has -SO3 (sulphonate) group
displacement
a redox reaction where a metal high in the electrochemical series reacts with a metal compound lower in the series
distillation
a process used for separating liquid mixtures. a liquid is boiled and its vapour then condensed to collect pure samples of the liquid. it is used to increase the percentage of ethanol after fermentation
electrochemical series
a list of chemicals arranged in order of their increasing ability to gain electrons, in other words in order of increasing oxidising power
electrolysis
the process which occurs when a current of electricity is passed through a molten electrolyte (resulting in decomposition) or an electrolyte solution (resulting in decomposition of the solute and/or the water)
electronegativity
the strength of the attraction by an atom of an element for its bonding electrons. if the electronegativities of two atoms sharing electrons are similar the bond will be almost purely covalent. the greater the difference in electronegativities the more likely the bond is to be polar covalent or even ionic
emulsifier
a compound which allows oil and water to mix
emulsion
a mixture of liquids where small droplets of one liquid are dispersed in another liquid. emulsions of oil and water are commonly found in food
endothermic reaction
a reaction where heat energy is absorbed from the surroundings. positive enthalpy change
end-point
the point in a titration where the indicator changes colour to indicate the reaction is complete
enthalpy change
the difference in heat energy between reactants and products in a reaction
enthalpy of combustion
the enthalpy change when one mole of a substance is completely burnt in oxygen
enzyme
a globular protein which is able to catalyse a specific reaction
equilibrium
state attained in a reversible reaction when forward and reverse reactions are taking place at the same time
essential oils
oils extracted from plants. they have distinctive smells, are non-polar, volatile and contain compounds known as terpenes
esters
carbon compounds formed when alcohols react with carboxylic acids by condensation
exothermic reaction
a reaction where heat energy is released to the surroundings. negative enthalpy change
fats
esters formed from one molecule of glycerol and three molecules of, usually saturated, long chain carboxylic acids. the compounds have melting points high enough to be solid at room temperature.
fatty acids
carboxylic acids formed from the hydrolysis of fats and oils
feedstock
a substance derived from a raw material which is used to manufacture another substance
fermentation
the process catalysed by enzymes in yeast which converts sugars into ethanol and carbon dioxide. this is known as alcoholic fermentation
free radicals
highly reactive atoms or molecules with unpaired electrons
free radical scavenger
a compound added to plastics, cosmetics and foods to prevent free radical reactions. these scavengers react with free radicals to produce stable molecules and terminate the reaction
gas liquid chromatography (GLC)
a technique used to separate mixtures in gas phase
glycerol
propan-1,2,3-triol; formed form the hydrolysis of fats and oils
haber process
industrial production of ammonia from nitrogen and hydrogen using high pressure and temperature, with iron as a catalyst
hess’s law
the enthalpy change of a chemical reaction depends only on the chemical nature and physical state of the reactants and products and is independent of any immediate steps
homologous series
a group of chemically similar compounds which can be represented by a general formula. physical properties change progressively through the series, for example the alkanes show a steady increase in boiling point
hormones
chemicals, often complex proteins, which regulate metabolic processes in the body. an example is insulin which regulates sugar metabolism
hydration
the addition of water to an unsaturated compound, for example the hydration of ethene C2H4 produces ethanol C2H5OH
hydrocarbon
a compound containing elements carbon and hydrogen only
hydrogenation
the addition of hydrogen to an unsaturated compound; for example hydrogenation converts alkenes to alkanes and oils into fats
hydrogen bonds
intermolecular forces of attraction. the molecules must contain highly polar bonds in which hydrogen atoms are linked to very electronegative nitrogen, oxygen or fluorine atoms. The hydrogen atoms are then left with a positive charge and are attracted to the electronegative atoms of other molecules. They are a specific, stronger type of PDPD interaction.
hydrolysis
the breaking down of larger molecules into smaller molecules by reaction with water
hydrophilic
parts of a molecule which are attracted to water, for example the -OH group in alcohols
hydrophobic
parts of a molecule which repel water for example the long hydrocarbon chains in fats and oils
hydroxyl group
the -OH group; it is found in alcohols
intermolecular bonding
bonds between molecules such as LDF, PDPF interactions and hydrogen bonds. these are much weaker than intramolecular bonds
intramolecular bonding
bonds within molecules such as covalent and polar covalent bonds
ionic bond
bond formed as a result of attraction between positive and negative ions
ionisation
the loss or gain of electrons by neutral atoms to form ions
ionisation energy
the energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state
ions
atoms or groups of atoms which possess a positive or negative charge due to loss or gain of electrons
isomers
compounds which have the same molecular formula but different structural formulae.
isotopes
atoms of the same element which have different numbers of neutrons. they have the same atomic number but different mass number
ketones
carbon compounds which contain the carbonyl group (C=O). formed from oxidation of secondary alcohols. cannot be oxidised using mild oxidising agents
Le Chatelier’s principle
if any change of physical or chemical conditions is imposed on any chemical equilibrium then the equilibrium alters in the direction which tends to counteract the change of conditions
London dispersion force
a force of attraction between all atoms and molecules formed from temporary and induced dipoles
mass number
the total number of protons and neutrons in the nucleus of an atom
metallic bonding
the bonding responsible for typical metallic properties : malleability, ductility and electrical conductivity in metals and alloys. each atom loses its outer electrons to form positive ions. these pack together in a regular crystalline arrangement with the electrons delocalised through the structure, binding the ions together
miscibility
the ability of liquids to mix perfectly together. in contrast, immiscible liquids form clearly defined layers with the denser liquid being the lower layer
mobile phase
in chromatography, the moving part of the process; for example the inert gas in GLC which carries the mixture of compounds through the column, or the solvent in paper chromatography which carries the mixture of compounds up the paper
molar bond enthalpy
the energy required to break one mole of covalent bonds
molar volume
the volume of one mole of a gas at a specified temperature and pressure
monatomic
a term used to describe the noble gases that are composed of individual atoms which do not bond to each other. they are held together by LDF in liquid and solids state
non-polar covalent bond
a covalent bond where both atoms share the electrons equally. this occurs between all elements that exist as molecules (Cl2, S8) since the atoms joining are identical. it also occurs in compounds where the bonding atoms have a small difference in electronegativity such as hydrocarbons
oils
esters formed from one molecule of glycerol and three molecules of typically unsaturated carboxylic acid. oils have melting points low enough to be liquids at room temperature
oxidation
a process where electrons are lost
oxidising agent
a substance which gains electrons or accepts electrons
peptide link
amide link but in a protein
permanent dipole-permanent dipole interactions
the attraction between molecules which possess a permanent dipole because of the presence of polar bonds
polar covalent bonds
bonds formed between non-metallic atoms by sharing a pair of electrons. if the atoms have considerably different electronegativities, the electrons are not shared equally, the more electronegative atom becoming slightly negative in comparison to the other atom.
polymer
a large molecule which is formed by joining together many smaller molecules (monomers)
polymerisation
the process where a polymer is formed
raw material
a useful substance for the chemical industry which found naturally, for example crude oil, water, air, metallic ores, coal, etc. can be made into feedstocks
redox reaction
a reaction where reduction and oxidation happen at the same time. electrons are lost by one substance and gained by another
redox titration
an experiment which the volumes of aqueous solutions of a reducing agent and an oxidising agent, which react together completely, is measured accurately.
reducing agent
a substance which loses electrons or is an electron donor
reduction
a process where electrons are gained
reproducibility
results obtained from an experiment are said to be reproducible if the same data can be obtained when the experiment is repeated. an experiment with good reproducibility will produce the same results again and again when carried out
retention time
the length of time it takes a substance to reach the detector after being injected into the chromatography column
rogue data
results that are unusual or do not fit pattern of expected results
screening
the ability of electrons in the inner energy levels to reduce the attraction of the nuclear charge for the electrons of the outermost levels
standard solution
a solution of a known concentration
stationary phase
in chromatography it is the phase other than the mobile phase. for example the liquid in GLC
temporary dipole
formed in all atoms where an excess of electrons is formed at one part of the atom. temporary dipoles are the basis for LDF
terpene
unsaturated compounds found in many plant oils. they are formed from the joining together of isoprene units
triglyceride
the molecules found in fats and oils. formed from one glycerol molecule joining to three fatty acid molecules
uv light
a high energy form of radiation which can break bonds in molecules, causing free radicals to form
van der waals’ forces
the forces of attraction that occur between all atoms and molecules known as intermolecular forces and include hydrogen bonding, PDPD and LDF. these are much weaker than covalent bonds
