Thermochemistry definitions

Define enthalpy change of formation

Answer explanation

Standard enthalpy change of formation (ΔHf ) is the enthalpy change when one mole of a substance is formed from its elements in their standard states under standard conditions.

define bond enthalpy

Answer explanation

Bond enthalpy is the enthalpy change when one mole of covalent bonds, in a gaseous molecule, is broken under standard conditions.

define first ionasation energy

Answer explanation

First ionisation energy is the enthalpy change when one electron is removed from each atom in one mole of gaseous atoms under standard conditions:

M(g) → M+(g)+e−

Define second ionisation energy

Answer explanation

Second ionisation energy is the enthalpy change for the process: M+(g) → M2+(g)+e−

Define electron affinity

Answer explanation

First electron affinity is the enthalpy change when one electron is added to each atom in one mole of gaseous atoms under standard conditions:

X(g)+e− → X−(g)

Define second electron affinity

Answer explanation

Second electron affinity is enthalpy change for the process:

X−(g)+e− → X2−(g)

Define Lattice enthalpy

Answer explanation

Lattice enthalpy (∆Hlatt) is the enthalpy change when one mole of an ionic compound is broken apart into its constituent gaseous ions under standard conditions.

using an example define enthalpy change of hydration

Answer explanation

he enthalpy change when one mole of gaseous ions is surrounded by water molecules to form an ‘infinitely dilute solution’ under standard conditions.

For example:

Na+(g) → Na+(aq) ΔHhyd = −390 kJ mol−1