Thermodynamics

Standard state

The normal state of a substance under standard conditions of temperature (298K) and pressure (100 kPa)

Standard enthalpy change of formation, ∆H_f^°

The enthalpy change required to form 1 mole of a compound from its elements in their standards states at 298K and 101kPa.

Standard enthalpy change of combustions, ∆H_c^°

The enthalpy change when 1 mole of a compound is completely burned in oxygen under standard conditions of 298K and 100kPa

Enthalpy of combustion formulas

Q = mcΔT

ΔH = Q / n

Enthalpy of formation

Enthalpy change when one mole of a substance is formed from its constituent elements with all substances in their standard states.

Both endo/exo

2Na_(s) + 1/2O_2(g) → Na₂O_(s)

Enthalpy of combustion

Enthalpy change when one mole of a substance undergoes complete combustion in oxygen.

Exo

H_2(g) + 1/2O_2(g) →H₂O_(g)

First Ionisation enthalpy

The first ionisation energy is the enthalpy change when one mole of gaseous atoms loses one electron per atom to produce gaseous 1+ ions.

Endo, as e^- held in.

Mg_(s) → Mg⁺_(g) + e^-

Second Ionisation Enthalpy

The second ionisation energy is when one mole of gaseous 2+ ions is produced from one mole of 1+ ions.

Even more endo than first ionisation enthalpy.

Mg⁺_(s) → Mg²⁺_(g) + e^-

First electron affinity

The first electron affinity is the enthalpy change when one mole of gaseous atoms gains one electron per atom to produce gaseous 1- ions.

Exo, as e^- attracted.

O_(g) + e^- → O^-_(g)

Second Electron Affinity

The second electron affinity is the enthalpy change when one mole of gaseous 1- ions gains one electron per ion to produce gaseous 2- ions.

Endo, as O^- and e^- repel each other.

O^-_(g) + e^- → O^2-_(g)

Enthalpy of atomisation

Enthalpy change when one mole of gaseous atoms is produced from an element in its normal state.

Endo

1/2I_2(g) → I_(g)

Hydration Enthalpy

Enthalpy change when one mole of gaseous ions become hydrated (dissolved in water). 

Exo

Mg²⁺_(g) → Mg²⁺_(aq)

Enthalpy of solution

Enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other.

Endo, sometimes exo.

MgCl_2(s) → Mg²⁺_(aq) +2Cl^-_(aq)

Bond Dissociation enthalpy

Enthalpy change when one mole of covalent bonds is broken in the gaseous state. 

Endo

I_2(g) → 2I_(g)

Lattice enthalpy of formation

Enthalpy change when one mole of a solid ionic compound is formed from into its constituent ions in the gas phase.

Exo

Mg²⁺_(g) + 2Cl^-_(g) →MgCl_2(s)

Lattice enthalpy of dissociation

Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase.

Endo

MgCl_2(s) → Mg²⁺_(g) + 2Cl^-_(g)