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Types of Enthalpy Changes 

Standard Enthalpy of Combustion delta Hc

The enthalpy change when one mole of a substance is completley combusted in oxygen under standard conditions (298 K and 100 kPa Pressure.

First Ionization Enthalpy

Enthalpy change when removing one mole of electrons from one mole of gaseous atoms

 

For example: Na (g) ----> Na+ (g) + e-

First Ionization Enthalpy

Enthalpy change when removing one mole of electrons from one mole of gaseous atoms

 

For example: Na (g) ----> Na+ (g) + e-

Standard Enthalpy of Formation delta Hf 

Enthalpy change when one mole of the compound is formed in its elements in their standard states at 298 K and 100 kPa Pressure. Following this, delta Hf for an element in its standard state will be zero.

Enthalpy of Atomisation 

Standard enthalpy of atomisation is the standard enthalpy change wehn one mole of gaseous atoms is formed from the  element in its standard state under standard conditions. For diatomic molecules this is equal to half the bond dissociation enthalpy.

eg)

 

1/2 Cl2(g) ----> Cl(g) delta Hat = +121kJ mol-1

Lattice Enthalpy

Lattice Enthalpy linked to either endothermic process of converting a crystalline solid into its gaseous ions OR to the exothermic process where the gaseous ions are converted into a crystalline solid.

 

MX (s) (↔)m + (g) + X (-) (g)

 

Lattice enthalpy sign indicator of whether lattice bons are being broken (-) or formed (+)

 

Lattice enthalpy sie is ependent on the size of teh ions and on the charge carried by the ions. The greater the charge, the smaller the ion and the higher the value of the lattice enthalpy.

Standard Enthalpy of Neutralization

The enthalpy change when 1 mole of acid is neutralized by an alkali under standard conditions at 1 molar

 

HCl (aq) +NaOH(aq) ---> HcO(l) + NaCl (aq)

Second Ionization Enthalpy

 

Enthalpy change when removing one mole of electrons from one mole of gaseous cations (specifically X+)

 

for example; Mg+ (g) ----> Mg2+ (g) + e-

First Electron Affinity

Enthalpy change when adding 1 mol of electrons (e-) to one mole of atoms in the gaseous phase

 

for example: O (g) + e- ----> O-

Electron affinity (first) usually is exothermic

Enthalpy Change of Hydration 

Enthalpy change when addign one mol of gaseous ions to water to form a dilute solution

for example ;

Na+ (s) ----> Na + (aq)

This is ALWAYS NEGATIVE

If the solvent is not water, "solvation" is used instead of "hydration."

Second Electron Affinity

Enthalpy change when adding one mole of electrons (e-) to 1 mole of anions (specifically X-)

 

For example; O- (g) + e- -----> O2- (g)

Most often an endothermic process

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