AS edexcel chemi definiftions

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Symbols
are used to represent elements, eg Fe for iron and C for carbon
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Formulae
are used to represtent compounds, eg H2O for water and NaCl for sodium chloride
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Molecular formula
shows the numbers of atoms of the different elements in one molecule of an compound, eg. CH4 for methane and C2H6 for ethane
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Empirical formula
shows the simplest whole number ratio of the atoms of different elements in a compound. eg CH4 for methane and CH3 for ethane
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balanced chemical equation
desribes a chemical reaction using symbols for the reactants and products. The numbers of each kind of atom are the same on both sides of the equation
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thermal decomposition
is the breaking up of substances into simpler substances by heating
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spectator ions
are ions which take no part in a reaction
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acids
are substances which donate hydrongen ions, H+ (protons)
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bases
are substances which accept hydrogen ions, H+ (protons)
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Alkalis
are soluble bases
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neutralisation
occurs when H+ ions react with OH- or O2- ions forming water
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salts
are the ionic compounds formed when an acid reacts with a base. Most salts are metal/non-metal compounds
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relative molecular mass
is the sum of the relaive atomic masses of all the atoms in its molecular formula
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relative formular mass
is the sume of the relative atomic masses of all the atoms in its formula
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Molar mass
is the mass of one mole of a chemical - the unit is gmol-1. As always with molar amounts , the symbol ot formula of the chemical must be specified
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molar volume
is the volume of 1 mole. At room temperature and atmospheric pressure, the molar volume of all gasses is 24dm3mol-1
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concentration/ gdm-3
= moss of solute/g / volume of solution/dm3
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concentration/ moldm-3
= amount of solute/mol / volume of solution/dm3
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actual yeild
is the mass of the product obtained
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Theoretical yeild
is the mass of the product obtained if the reaction goes according to the equation
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percentage yeild
= (actual yeild / theretical yeild) x100
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limiting reactant
is a substance which is present in an amount which limits the theoretical yeild. Often some reactants are added in excess to ensure that the most valuble reactant is converted to as much product as possible.
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Atom economy
= (mass of atoms in desired product / mass of atoms in all reactants) x100
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enthalpy change
is the overall energy exchanged with the surroundings when a change happens at constant pressure and the final tempurature is the same as the starting temperature
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specific heat capacity, c
is the energy needed to raise the temperature of 1g of material by 1K for water c = 4.2Jg-1K-1
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the standard enthalpy change of reaction
is the energy transferred when the molar quantities of reactant as started in the equation react under standard conditions
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the standard enthalpy change of neutralisation
is the enthalpy change when the amounts of acid and alkali in the equation for the reaction neutralise each other under standard conditions
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the standard enthalpy change of combustion
is the enthalpy change when one mole of the substance burns completely in oxygen under standard conditions
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the standard enthalpy of formation
is the enthalpy change when one mole of the compound forms from its elements under standard conditions with the elements and the compound in their standard states
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the standard enthalpy change of atomisation
id the enthalpy change when one mole of gaseos atoms is formed from the element under standard conditions
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Hess's Law
says that the enthalpy change in converting reactants to products is the same regardless of the route taken, provided the initial and final conditions are the same
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bond enthalpy
of a particular bond is the energy required to break one mole of the bonds in a substance in the gaseous state
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atomic number
of an atom is the number of protons in its nucleus. (Atomic number)
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mass number
of an atom is the number of protons plus neutrons in its nucleus. (nucleon number)
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Isotopes
atoms of the same element with the same atomic number, but different mass number
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relative isotopic mass
is the mass of one atom of an isotope relative to the mass of one atomfir of carbon-12, for which the relative mass is definied as exactly 12
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first ionisation energy
is the energy needed to remove one electron from each atom in one mole of gaseous atoms
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an orbital
is a region of space around the nucleus of an atom in which there is a 95% chance of finding an electron, or pair of electrons with opposite spins
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electron configuration
decribes the number and arrangement of electrons in an atom.
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lattice
to describe a regular arrangement of atoms or ions in a crystal
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Delocalised electrons
are bonding electrons which are not fixed between two atoms in a bond. They are free to move and are shared by several or many atoms
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metalic bonding
is the strong attraction between a lattic of positive metal ions and a 'sea' of delocalised electrons.
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electrolysis
is the decomposition of a compound by eletricity- the compound is usually decomposed into it constituent elements. The compound which is decomposed is called an electrolyte and we say that it has been electrolysed
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the first electron affinity
is the energy chane when each atom in one mole of gaseous atoms gain one electron to form one mole of gaseous ions with a single negative charge
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lattice energy
is the standard enthalpy change when one mole of the compound forma from free gaseous ions
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polarisation
is the distortion of the electron cloud in a molecule or ion by nearby charge
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Dative covalent bond
is a bond in which two atoms share a pair of electrons, both the electrons being donated by one atom
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functional group
is the group of atoms which gives an organic compound its characteristc properties and reactions
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structual formula
shows in minimal detail which atoms, or groups of atoms, are attached to each other in one molecule of a compound
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displayed formula
shows all the atoms and all the bonds between them in one molecule of a compound
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skeletal formular
shows the functional group fully, but the hydrocarbon part of a molecule, simply as lines between carbon atoms and hydrogen atoms
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structural isomers
are compounds with the same molecular formula but different structural formulae
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free radicals
highly charged single atoms, or groups of atoms, with unpaired electrons
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nucleophiles
are ions or molecules with a lone pair of electrons that attack positive ions or positive centres
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electrophiles
are reactive ions and molecules which attack negative ions or negative centres in molecules
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aliphatic hydrocarbons
are straight-chain and branched hydrocarbonswith no rings of carbon atoms
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alicyclic hydrocarbon
are hydrocarbons with at least one ring of carbon atoms
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arenes
are hydrocarbons with a ring or rings of carbon atoms in which there are delocalised electrons
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substitution reaction
is one in which an atom, or group of atoms is replaced (substituted) by another atom, or group of atoms.
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intiation
the step which produces free radicals
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propagation
steps which form products and more free radicals
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termination
steps which remove free radicals by turning them into molecules
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sustainable lifestyle
involves living within the means of the environment in order that the Earth's natural resources are available for future generations
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unsaturated
compounds contain one or more double or triple bonds between atoms in their molecules. The term is often applied to alkenes and to describe unsaturated fats which have C=C double bonds in the hydrocarbon chains
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cis and trans isomers
are molecule with same molecular formula, the same structural formula, but different displayed formulae
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addition reaction
is a reaction in which two molecules add together to form a single product
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Intermediates
are atoms, molecules ions or free-radicals which do not appear in the overall equation for a reaction, but which are formed during one step of a reaction and then used up in the next
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Addition polymerisation
is an addition reaction in which small molecules, called monomers, join together forming a giant molecule, called a polymer.
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bond angle
is the angle between two covalent bonds in a molecule or giant covalent structure
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bond angle
is the distance between the nuclei of two atoms linked by one or more covalent bonds. For the same two atoms, triple bonds which, in turn are shorter than double bonds which, in turn, are shorter than single bonds.
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Allotropes
are different forms of the same element in the same physical state
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composities
combine two or more materials to create a new material which has the more desirable properties of both it consituents.
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polar covalent bonds
are bonds between atoms of different elements. The shared electrons. The bonds have a positive pole at one end and a negative pole at the other.
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elctronegavitivity
is a measure of the pull of an atom of an element on the shared electrons in a covalent bond. In a polar bond the shared electrons are draw towards the more electronegative atom.
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polar molecules
have polar bonds which do not cancel each other out, so that the whole molcule is polar
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Intermolecular forces
are weak attractive forces between moloecules
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London forces
are the intermolecular forces between all molecules. The arise from the attraction between temporary dipoles they induce in neighbouring molecules
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Polarisability
is an indication of the extent to which the electron cloud in a molecule can be distorted by a nearby electric charge
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hydrogen bonding
is a type of attraction between molecules which is much stronger than other types of intermolecular force, but much weaker than covalent bonding
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a solute
is a chemical which dissolves in a sovlent to make a solution
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saturated solution
ccontains as much of the solute as possible at a particular temperature
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solubility
is a measure of the concentration of a saturated solution of a solute at a specified tempurature
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non-aqueous solvent
is any solvent other than water
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miscrible
are liquids that mix with each other
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hydration
takes place when water molecules bond to ions or add to molecules. Water molecules are polar so they are attracted to both positive ions and negative ions
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ionic equation
decribes the chemical changes by showing only the reacting ions, leaving out spectator ions
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half-equation
is an ionic equation used to describe either the gain or the loss of electrons during a redox reaction
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oxidation
the gain of oxygen, loss of electrons or the loss of hydrogen
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reduction
the loss of oxygen, gain of electrons or the addition of hydrogen
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basic oxidation
is a metal oxide which reacts with acids to form salts and water. The oxide ions acts as a base and accepts the hydrogen from the acid. Oxides which disolve in water are alkalis
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disproportionation
is a change in which the same element both increases and decreases its oxidation number. So the element is both oxidised and reduced
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a standard solution
is a solution with an acurately know concentration.
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primary standard
is a chemical which can be weighed out accurately to make up a standard solution
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end-point
is the point during a titration when enough of the solution in the burette has been added to react exactl with the amount of chemical in the flask
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precise results
are mesurements that when repeated have a small random error
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bias
arises from systematic errors which can affect all the measurements in the same way, making them all higher or lower than the true value. They do not average out
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accurate results
are precise and free from bias
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chemical kinetics
is the study of the rates of chemical reactions
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reaction profile
is a graph which shows how the total enthalpy (energy) of the atoms, molecules or ions changes during the process of a reaction from reactants to products
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activation energy
is the height of the energy barrier separating reactants and products during a chemical reaction. It is the minimum energy needed for a reaction between the amounts, in moles, shown in the equation for the reaction
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primary
the functional group is at the end of the chain
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secondary
the functional group is somewhere along the chain
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tertiary
the functional group is on a branch on the chain
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reflux condenser
is fitted to a flask to prevent vapour escaping while a liquid is beatin heated
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hydrolysis
is a reaction in which a compound splits in a reaction involving water
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the mass to charge ratio
is the ratio of the relative mass of an ion to its charge, where e is the number of charges.
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absorption spectum
is a plot showing how strongly a chemical absorbs radiation over a range of frequecies
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wavenumber
is the number of waves in 1cm
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transmittance
measures the percentage of radiation which passes through the sample. The troughs appear at those wavenumbers where the compound absorbs strongly
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green chemistry
is the design of chemical processes and products that reduce or eliminate the production and use of hazardous chemicals
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sustainalble development
meets the needs of the presents without compramising the ability of future generations to meet their own needs
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anthropogenic effects
are the changes brought about by human activities. they include factors that affect the atmophere, such as burning fossil fules, deforesation and intensive agriculture
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carbon footprint
measures the total amount of greenhouse gasses produced by a process or product in tonnes of carbon dioxide
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coarbon dioxide equivilent, CO2 eq.
is the measure of in terms of the quantity of carbon dioxide that would have the same global warming effect
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carbon neutal
is a process where the CO2 released is balances by actions which remove an equivalent amount of CO2 from the atmosphere
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Card 2

Front

are used to represtent compounds, eg H2O for water and NaCl for sodium chloride

Back

Formulae

Card 3

Front

shows the numbers of atoms of the different elements in one molecule of an compound, eg. CH4 for methane and C2H6 for ethane

Back

Preview of the back of card 3

Card 4

Front

shows the simplest whole number ratio of the atoms of different elements in a compound. eg CH4 for methane and CH3 for ethane

Back

Preview of the back of card 4

Card 5

Front

desribes a chemical reaction using symbols for the reactants and products. The numbers of each kind of atom are the same on both sides of the equation

Back

Preview of the back of card 5
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