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A2 Chemistry OCR Definitions: Rates, acids and enthalpy
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NB: Not official list of definitions, these are only ones I have in my notes
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Ollie O'Keeffe
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Ollie O'Keeffe
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A2 Chemistry OCR Definitions: Rates, acids and enthalpy
Enthalpy change
Enthalpy change of atomisation
The enthalpy change when 1 mole of gaseous atoms forms the element at 298K, 101kPa
1st Ionisation energy
The energy needed to remove 1 electron from every atom in 1 mole of gaseous atoms, to form 1+ ions
2nd Ionisation energy
Energy needed to remove the second electron from every atom in 1 mole of gaseous 1+ ions
Lattice enthalpy
The enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions, at 298K, 101kPa
Enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from its elements, at 298K, 101 kPa
Standard enthalpy of electron affinity
Enthalpy change when 1 electron is gained by every atom in 1 mole of gaseous atoms, to form 1- ions
NB: 1st EA always exothermic, 2nd & 3rd always endothermic
Enthalpy change of solution
Enthalpy change when 1 mole of an ionic compound dissolves in sufficient water to make a very dilute solution, at 298K, 101kPa
NB: Exothermic = Soluble
Enthalpy change of hydration
The enthalpy change when 1 mole of gaseous ions dissolves in sufficient water to form a very dilute solution
Enthalpy of neutralisation
Enthalpy change when enough acid/alkali is neutralised to make 1 mole H2O
Hess' Law
The enthalpy change going from reactant to product is independent of the route taken
Acids/bases
Acid
Proton donor
Base
Proton acceptor
Strong acid
One that ionises fully
Weak acid
One that only partially ionises
Conjugate acid/base pairs
A conjugate acid becomes its own conjugate base when it gives a H+ to another base. Vice versa for base
NB: If conj. acid is v/ strong, conj. base is v/ weak
Kw
Ionic product of water
NB: 1x10-4
pH
-log(Concentration of H+)
Ka
Acid dissociation constant
Indicators
Weak acids which have 2 colours (one for acid, one for its conj. base)
Buffer
A system that minimises pH changes on addition of moderate amounts of acid/alkali
Rates
Rate of Reaction
How the concentration of a reactant decreases over time
Order
The power to which we raise the conc. of a particular reactant in a rate equation
Rate constant (k)
The proportionality constant in a rate equation
Rate Determining Step (RDS)
The slowest step in a reaction mechanism (series of reactions not shown in overall reaction)
Determines overall rate
Half-life
The time taken for the concentration of a reactant to halve
Free energy (ΔG)
The balance between enthalpy, entropy and temperature for a process
NB: Reaction is spontaneous is ΔG<0
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