Definitions Flashcards
1
Q
CIS/TRANS ISOMERISM
A
A special case of E/Z isomerism in which two of the substituent groups attached to each carbon atom of the C=C group are the same (these are often, but not always, a H atom).
2
Q
REDUCING AGENT
A
A reagent which reduces another species (and is itself oxidised) by losing electrons.
3
Q
PRECIPITATE
A
An insoluble solid formed when two solutions are mixed together.
4
Q
DYNAMIC EQUILIBRIUM
A
Exists in a closed system when the rate of ten forward reaction is equal to the rate of the reverse reaction and the concentrations of reactants and products do not change.
5
Q
AVERAGE BOND ENTHALPY
A
The average enthalpy change for the breaking of one mole of bonds in gaseous molecules (by homolytic fission).
6
Q
BASE (BRONSTED-LOWRY)
A
Proton acceptor.
7
Q
ATOMIC NUMBER
A
The number of protons in the nucleus of an atom.
8
Q
Le CHATELIER’S PRINCIPAL
A
When a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the effects of the change.
9
Q
STRONG ACID
A
A proton donor which completely dissociates into its ions in solution.
10
Q
OXIDISING AGENT
A
A reagent which oxidises another species (and is itself reduced) by gaining electrons.
11
Q
ENTHALPY CHANGE
A
The amount of heat released (or absorbed) by a chemical reaction, carried out at constant pressure. Units: kJ mol-1.
12
Q
PI () BOND
A
Double sideways overlap of adjacent p orbitals above and below the plane of the bonding atoms, with restricted rotation of the bond.
13
Q
METALLIC BONDING
A
The strong electrostatic attraction between metal cations (positive ions) and delocalised electrons (in a giant metallic lattice structure).
14
Q
CATALYST
A
Increases the rate of a reaction without being used up by the overall reaction. It allows the reaction to proceed via a different route with lower activation energy.
15
Q
OXIDATION
A
The loss of electrons / an increase in oxidation number (state).
16
Q
RETENTION FACTOR
A
Distance moved by the component (from base line)/distance moved by solvent front (from base line).
17
Q
OXIDATION REACTION
A
A reaction where oxygen is added and/ or hydrogen is removed from a molecule.
18
Q
STRUCTURAL ISOMERS
A
Compounds with the same molecular formula but different structural formulae.
19
Q
ALICYCLIC
A
An aliphatic compound arranged in non-aromatic rings with or without side chains.
20
Q
STANDARD ENTHALPY CHANGE OF HYDRATION
A
The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions.
21
Q
(GIBBS) FREE ENERGY CHANGE
A
The balance between the enthalpy change (ΔH), the entropy change (ΔS) and temperature (T) for a process. ΔG = ΔH - TΔS ΔG, determines the feasibility of a reaction: a reaction is feasible if ΔG < 0.
22
Q
SALT
A
A compound produced when a H+ ion from an acid is replaced by a metal ion or another positive ion, such as the ammonium ion.
23
Q
CHROMATOGRAPHY
A
An analytical technique that separates components in a mixture between a mobile phase and a stationary phase.
24
Q
ANHYDROUS
A
Describes a substance that does not contain water.
25
DEGRADABLE POLYMER
A polymer that breaks down into smaller fragments when exposed to light, heat or moisture.
26
IONIC PRODUCT OF WATER
The dissociation of water: H2O H+ + OH- Kw = [H+] [OH-] units = mol2dm-6 At 250C Kw = 1.00 x 10-14 mol2dm-6.
27
HYDRATED
When water of crystallisation is present in a crystal compound.
28
MOBILE PHASE
The phase which moves in chromatography; a liquid (TLC) or a gas (GC).
29
MOLECULAR FORMULA
The actual number and type of atoms of each element in a molecule.
30
DISPLACEMENT REACTION
A reaction in which a more reactive element (halogen) displaces a less reactive element (halogen) from an aqueous solution of its halide ions.
31
PERIODICITY
The repeating pattern of chemical and physical properties across different periods.
32
SIGMA () BOND
Single end-on (axial) overlap of orbitals directly between bonding atoms, allowing free rotation of the bond.
33
COVALENT BOND
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
34
RETENTION TIME
The time taken from a component to pass from the column inlet to the detector (in GC).
35
STANDARD CELL POTENTIAL
Eθcell = Eθreduction - Eθoxidation For a reaction to be feasible, the species undergoing reduction must have the more positive Eθ value: Eθcell > 0.
36
ACID (BRONSTED-LOWRY)
Proton donor.
37
MOLE FRACTION
Number of moles of A/total number of moles in gas mixture.
38
ALIPHATIC
A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings.
39
STANDARD ENTHALPY CHANGE OF SOLUTION
The enthalpy change when one mole of a compound is completely dissolved in water under standard conditions.
40
ENDOTHERMIC REACTION
A reaction where heat energy is absorbed from the surroundings. (ΔH is positive).
41
CURLY ARROW
The movement of an electron pair, showing either heterolytic fission or formation of a covalent bond.
42
MOLE
The amount of substance containing as many particles as there are carbon atoms in exactly 12g of Carbon-12.
43
STEREOISOMER
Compounds with the same structural formula but with a different arrangement of the atoms in space.
44
DEHYDRATION REACTION
A reaction where a H2O molecule is removed from a saturated molecule to form an unsaturated molecule.
45
RATE OF REACTION
The change in concentration of a reactant or product per unit time.
46
EXOTHERMIC REACTION
A reaction where heat energy is released to the surroundings. (ΔH is negative).
47
OPTICAL ISOMERISM
An example of stereoisomerism in which there is a pair of non-superimposable mirror images of one another, about a chiral centre.
48
HOMOLYTIC FISSION
The breaking of a covalent bond where each bonding atom receives one electron from the bonding pair of electrons, forming two radicals.
49
RELATIVE ISOTOPIC MASS
The mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12.
50
IONIC BOND
The electrostatic attraction between positive and negative (oppositely charged) ions.
51
STRUCTURAL FORMULA
The minimum detail required to show the arrangement of atoms in a molecule, e.g. for butane: CH3CH2CH2CH3 or CH3(CH2)2CH3.
52
DISPLAYED FORMULA
shows the relative positioning of atoms and the bonds between them, e.g. for ethanol:
53
AROMATIC
A compound containing a benzene ring.
54
LIGAND
A molecule or ion that can donate a pair of electrons with the transition metal ion to form a coordinate bond.
55
COORDINATION NUMBER
The total number of coordinate bonds formed between a central metal ion and its ligands.
56
MOLAR GAS VOLUME
The gas volume per mole of a substance. This is 24.0 dm3mol-1 at room temperature and pressure (RTP).
57
-AMINO ACID
Molecule with general formula RCH(NH2)COOH.
58
HYDROCARBON
Compounds composed of only carbon and hydrogen.
59
DATIVE (CO-ORDINATE BOND)
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms, where only one of the atoms supplies both the electrons shared.
60
CONDENSATION POLYMERISATION
The joining of monomers with the elimination of a small molecule such as water.
61
ALKALI
A base that dissolves in water and releases OH- ions in aqueous solution.
62
WATER OF CRYSTALLISATION
Water molecules that are bonded into a crystalline structure of a compound.
63
REDUCTION
The gain of electrons / a decrease in oxidation number (state).
64
AVOGADRO’S CONSTANT
The number of particles per mole of a substance (6.02 x 1023 mol-1).
65
STANDARD STATES
Physical states under standard conditions.
66
STATIONARY PHASE
The phase that does not move in chromatography; a solid (TLC) or a liquid on a solid support (GC).
67
MASS NUMBER
The total number of protons and neutrons in the nucleus of an atom.
68
UNSATURATED
Containing at least one multiple carbon-carbon bond, including C=C, C=C and aromatic rings.
69
d-BLOCK ELEMENT
Element which has the highest energy electron in a d sub-shell (or d orbital).
70
LIGAND SUBSTITUTION
A reaction in which one ligand in a complex ion is replaced by another ligand.
71
TRANSITION ELEMENT
d block element that has an ion with an incomplete d sub-shell.
72
HETEROLYTIC FISSION
The breaking of a covalent bond where one bonding atom receives both electrons from the bonding pair of electrons, forming two oppositely charged ions.
73
DISTILLATION
The technique of heating a liquid to create vapour which is collected when cooled and condensed, separate from the original liquid. (often used to separate liquids based on their boiling points).
74
SKELETAL FORMULA
The simplified organic formula, shown by 'hiding' every C atom and any H atom which is directly attached to a C atom, leaving just the carbon skeleton and any functional groups. e.g. for butan-2-ol:
75
VOLATILITY
The ease with which a liquid turns into a gas.
76
CONJUGATE ACID-BASE PAIR
A pair of two species that transform into each other by the gain or loss of a proton (H+).
77
RELATIVE ATOMIC MASS
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.
78
RATE EQUATION
Gives the relationship between the rate of reaction and the concentration of the reactants raised to the powers of their orders. Example, for the reaction: A + B products Rate equation: rate = k [A]m [B]n.
79
FIRST IONISATION ENERGY
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
80
SATURATED
Containing single carbon-carbon bonds only.
81
ATOMIC ORBITAL
A region around the nucleus that can hold up to two electrons, with opposite spins.
82
HESS’ LAW
The enthalpy change of a reaction depends only on the initial and final states and is independent of the route taken.
83
ELECTRON PAIR REPULSION THEORY
• The shape of simple covalent molecules and ions are determined by the number & type of electron pairs around the central atom.
• Electron pairs repel one another as far apart as possible • Lone pairs of electrons repel more strongly than bond pairs of electrons.
84
FUNCTIONAL GROUP
A group of atoms within a molecule responsible for the characteristic reactions of a compound.
85
DISPROPORTIONATION
A reaction in which the same element is both oxidised and reduced.
86
CONDENSATION REACTION
A reaction where an H2O molecule is lost when two molecules join together.
87
BUFFER SOLUTION
A system that minimises pH changes on addition of small amounts of an acid or a base.
88
OXIDATION NUMBER
A measure of the number of electrons that an atom uses to bond with atoms of another element.
89
LATTICE ENTHALPY
The enthalpy change when one mole of an ionic compound is formed from its gaseous ions under standard conditions
90
ADDITION REACTION
A reaction where a group is added across a double bond of an unsaturated molecule to make a saturated molecule (one product).
91
RATE-DETERMINING STEP
The slowest step of a reaction mechanism of a multi-step reaction.
92
HOMOLOGOUS SERIES
A series of organic compounds with the same functional group but with each successive member differing by CH2.
93
STANDARD CONDITIONS
• Temperature = 25 oC (298 K)
• Pressure of gases = 1 atm (100 kPa)
• Concentration of (aq) solutions = 1.00 moldm-3
94
STANDARD ENTHALPY CHANGE OF FORMATION
The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.
95
STANDARD ENTHALPY OF COMBUSTION
The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions.
96
SOLUTION
A homogeneous mixture composed of two or more substances. A solution consists of a solute and a solvent. The solute is the substance that is dissolved in the solvent. These are usually transparent.
97
CHIRAL CENTRE (carbon)
A carbon atom with four different groups attached.
98
SUCCESSIVE IONISATION ENERGY
A measure of the energy required to remove each electron in turn.
99
COMPLEX ION
A transition metal ion bonded to one or more ligands by coordinate bonds (dative covalent bonds).
100
STANDARD ELECTRODE (REDOX) POTENTIAL
The e.m.f. (electromotive force / voltage) of a half cell compared with a standard.
101
ELECTRONEGATIVITY
The ability of an atom to attract the bonding electrons towards itself in a covalent bond.
102
HEAT UNDER REFLUX
The continuous boiling and condensing of a liquid (in a condenser) preventing loss of volatile liquids from a heated reaction vessel.
103
HYDROLYSIS REACTION
A chemical reaction involving water or an aqueous solution, which causes the breaking of a bond, splitting a reactant molecule into two products.
104
ACTIVATION ENERGY
The minimum energy required for a reaction to take place, by the breaking of bonds in the reactants.
105
HETEROGENEOUS CATALYST
Catalyst has a different physical state from the reactants (frequently, reactants are gases while the catalyst is a solid).
106
ALKYL GROUP
Of formula CnH2n+1.
107
HALF-LIFE
The time taken for the concentration of a reactant to fall to half of its original concentration. (For a first order reaction, half-life is constant).
108
BIDENTATE LIGAND
A ligand which can donate two lone pairs of electrons to the central metal ion to form two coordinate bonds.
109
HOMOGENEOUS CATALYST
Catalyst is in the same physical state as the reactants (frequently, the aqueous or gaseous state).
110
RATE CONSTANT
: 'k' in the rate equation: the larger the value of k, the faster the reaction. k is constant at a constant temperature and increases with temperature (Arrhenius).
111
ISOTOPES
Atoms of the same element with different numbers of neutrons.
112
PARTIAL PRESSURE
mole fraction of A x total pressure P.
113
GENERAL FORMULA
The simplest algebraic formula for any member of a homologous series, e.g. for an alkane: CnH2n+2.
114
FUEL CELL
A cell which uses the energy from the reaction of a fuel with oxygen to create a voltage.
115
ELIMINATION REACTION
A reaction where an atom or group is removed from a molecule to make an unsaturated molecule.
116
EMPIRICAL FORMULA
The simplest whole number ratio of atoms of each element present in a compound.
117
REDOX
A reaction where both oxidation and reduction take place.
118
E/Z ISOMERISM
An example of stereoisomerism in which there is restricted rotation about a C=C double bond, and each carbon atom of the C=C double bond has two different groups attached to it.
119
STANDARD ENTHALPY OF NEUTRALISATION
The energy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of H2O(l), under standard conditions.
120
NUCLEOPHILE
An electron pair donor.
121
MOLAR MASS
The mass in grams of one mole of a substance.
122
STANDARD ENTHALPY CHANGE OF REACTION
The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.
123
RADICAL
Species with an unpaired electron (e.g. Cl.)
124
ENTROPY
A measure of the dispersal of energy in a system which is greater, the more disordered a system.
125
ORDER
How the concentration of a reactant affects the rate of the reaction. In the rate equation above, Order with respect to A = m Order with respect to B = n Overall order = m + n.
126
EQUILIBRIUM CONSTANT
For an equilibrium reaction: A + B C + D Kc = [C]c [D]d Kp = p(C)c x p(D)d [A]a [B]b p(A)a x p(B)b [ ] = equilibrium concentrations p = partial pressures (for gases).
127
ACID DISSOCIATION CONSTANT
For a weak acid: HA H+ + A- Ka = [H+] [A-] units = moldm-3 [HA] and pKa = - log Ka.
128
BIODEGRADABLE POLYMER
A polymer that breaks down completely into CO2 and H2O.
129
ELECTROPHOLE
An electron pair acceptor.
130
p-BLOCK ELEMENT
Element which has the highest energy electron in a p sub-shell (or p orbital) (Applies to any element; s-, p-, d- or f-block).
131
WEAK ACID
A proton donor which partially dissociates into its ions in solution. pH pH = - log [H+] and [H+] = 10-pH.
132
SUBSTITUTION REACTION
A reaction where an atom or group in a molecule is replaced by another atom or group.
