Thermodynamics

Question 1

Enthalpy of formation (ΔfH)

Answer 1

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

exothermic for most substances

Question 2

Enthalpy of combustion (ΔcH)

Answer 2

Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in standard states.

exothermic

Question 3

Enthalpy of neutralisation (ΔneutH)

Answer 3

Enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions.

Exothermic

Question 4

Ionisation enthalpy (ΔieH)

Answer 4

First ionisation energy = enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions.

Second ionisation energy = enthalpy change when each ion in one mole of gaseous 1+ ions loses one electron to form one mole of gaseous 2+ ions.

endothermic

Question 5

Electron affinity (ΔeaH)

Answer 5

First electron affinity = enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions.

exothermic for many non-metals

Second electron affinity = enthalpy change when each ion in one mole of gaseous 1- ions gains one electron to form one mole of gaseous 2- ions.

endothermic (as adding -ve electron to -ve ion)

Question 6

Enthalpy of atomisation (ΔatH)

Answer 6

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

endothermic

Question 7

Hydration enthalpy (ΔhydH)

Answer 7

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

exothermic

Question 8

Enthalpy of solution (ΔsolH)

Answer 8

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.

varies

Question 9

Bond dissociation enthalpy (ΔdisH)

Answer 9

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

endothermic

Question 10

Lattice enthalpy of formation (ΔlefH)

Answer 10

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

exothermic

Question 11

Lattice enthalpy of disassociation (ΔledH)

Answer 11

Enthalpy when one mole of a solid ionic compound is broken up into it’s constituent ions in the gas phase

endothermic

Question 12

Enthalpy of vaporisation (ΔvapH)

Answer 12

Enthalpy change when one mole of a liquid is tuned into a gas.

endothermic

Question 13

Enthalpy of fusion (ΔfusH)

Answer 13

Enthalpy change when one mole of a solid is tuned into a liquid

endothermic