Definitions
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Define isotope
Atoms of an element with the same number of protons but different numbers of neutrons
Define relative atomic mass
Average mass of an atom of an element compared to one-twelfth of the mass of an atom of carbon-12
Define relative molecular mass
The average mass of a molecule relative to one-twelfth of the mass of an atom of carbon-12
Define relative formula mass
Total of relative atomic masses in a compound
Define isotopic abundance
Relative proportions of stable isotopes of each element
Define first ionisation energy
The energy needed to remove an electron from one mole of gaseous atoms to form one mole of gaseous 1+ ions
Avagadros constant and formula
6.022x10^23 = L Number of particles = moles x L
Ideal gas equation
pV = nRT
Define empirical formula and molecular formula
Empirical formula is the simplest whole number ratio of atoms of each element in a compound. Molecular formula is the actual number of atoms of each element in a compound
Define electronegativity
the power of an atom to attract the pair of electrons in a covalent bond
Define co-ordinate bond
bond containing a shared pair of electrons with both electrons supplied by one atom.
Define enthalpy change
change in heat energy under constant pressure
define standard enthalpy of combustion (∆cHƟ)
the enthalpy change when one mole of substance burns completely in oxygen under standard conditions in standard states
define standard enthalpy of formation (∆fHƟ)
the enthalpy change when one mole of substance is formed from its constituent elements in standard states under standard conditions
State Hess’ Law
The enthalpy change for a chemical reaction is independent of the route taken
Define mean bond enthalpy
The energy required to break a covalent bond in a molecule averaged over a range of compounds
Define activation energy
Minimum amount of energy required to start a reaction
Define rate of reaction
The change in concentration of a substance in a given time
Define catalyst
substance that increases the rate of a chemical reaction without being changed in chemical composition or amount work by providing an alternative reaction route of lower activation energy
State Le Chatelier’s principle
If a change is made to a system in dynamic equilibrium, the equilibrium position shifts to counteract this change
Define oxidation
Loss of electrons
Define reduction
Gain of electrons
Define oxidising agent
Electron acceptors
Define reducing agent
Electron donors