Physical AS definitions Flashcards
First ionisation energy
The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of +1 ions.
Relative atomic mass
The average mass of an atom of an element compared to carbon 12 on a scale in which an atom of Carbon 12 has a mass of 12.
Relative molecular mass
The average mass of a molecule of an element compared to carbon 12 on a scale in which a molecule of Carbon 12 has a mass of 12.
Empirical formula
The simplest whole number ratio of the types of atoms of each element in a compound.
Molecular formula
The actual number of each type of atom of each element in a compound.
Co-ordinate bond
A co-ordinate (dative covalent) bond contains a shared pair of electrons with both electrons supplied by one atom.
Dipole
The unequal sharing of the electron density of the covalent bond due to the difference of electronegativity between the elements involved.
Electronegativity
The power of an atom to attract the pair of electrons in a covalent bond.
Enthalpy change
Heat energy change measured under conditions of constant pressure.
Standard enthalpy of formation
The enthalpy change when one mole of a substance is formed from its elements under standard conditions
Standard enthalpy of combustion
The enthalpy change when one mole of a substance is burnt in oxygen under standard conditions.
Hess’ law
The enthalpy change for a chemical reaction is the same regardless of route taken from reactants to products.
Mean bond enthalpy
The energy required to break a covalent bond in a substance in the gaseous state, averaged over a range of compounds.
Activation energy
The minimum amount of energy for particles to collide with for a successful reaction to take place.
Rate of reaction
The amount of product formed or reactant used per unit of time.
