Enthalpy Flashcards
enthalpy of formation
enthalpy change when one mole of a compound is formed from its elements under standard conditions when all products are in their standard states
first ionisation energy definition
enthalpy change required to remove one mole of electrons
from one mole of gaseous atoms
to form one mole of gaseous +1 ions
electron affinity edinition
enthelpy change that occurs when 1 mole of gaseous atoms
gain 1 mole of electrons
to form 1 mole of gaseous ions with a -1 charge
enthalpy of atomisation definition
enthalpy change when 1 mole of gaseous atoms
is formed from the element in it’s standard state
under standard conditions
lattice enthalpy of formation definition
enthalpy change when 1 mole of ionic crystal
is formed from its constituent ions
in gaseous form
why is second ∆Hea always positive
energy is required to overcome repulsion between negatively charged ion and electron
why might enthalpy values calculated from bond enthalpies be inaccurate
known bond enthalpies are an average of many molecules
actual bond enthalpies specific to each molecule are likely to differ from the mean values
enthalpy of hydration definition
enthalpy change when 1 mole of gaseous ions become aqueous ions
why is first ∆Hea negative
energy is released as the electron is attracted to the nucleus
and therefore the negative ion is more stable than the atom
standard bond dissociation energy
energy required to break one mole of bonds with every substance in gaseous form
enthalpy of solution definition
enthalpy change when one mole of ionic salt dissolves in a large enough volume of water so that dissolved ions do not interact
equation linking enthalpies of solution and hydration
∆Hsol = ∆HLE + ∆Hhyd
perfect ionic model assumptions (3)
point charges
no covalent interactions
attraction is purely electrostatic
reasons for greater ∆HLE
smaller ions > charges closer
greater charges
what does low agreement between experimental and modelled ∆HLE suggest
the ionic salt has some covalent character
