Enthalpy Definitions

Question 1

Lattice enthalpy

Answer 1

Enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions

Eg k+ (g) + cl-(g) = KCl (s)

Question 2

Standard enthalpy change of formation

Answer 2

The enthalpy change taking place when one mole of a compound is formed from its element under standard conditions with all reactants and products in their standard states

Na (g) + 1/2cl2 (g) nacl (S)

Question 3

Standard enthalpy change of atomisation

Answer 3

Enthalpy change taking place for the formation of mole of gaseous atoms from the element in its standard state in standard conditions

Eg 1/2(cl)2(g)= cl(g)

Question 4

First ionisation energy

Answer 4

Enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

Na(g) = na+(g) + e-

Question 5

First electron affinity

Answer 5

The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Cl(g) +e- =cl- (g)

(First ones are exothermic as electron added is attracted to nucleus)

Question 6

Standard enthalpy change of solution

Answer 6

The enthalpy change that takes place when one mole of a solute dissolves in a solvent. If the solvent is water the ions from the ionic lattice finish up surrounded with the water molecules as aqueous ions

Na+cl-(S) +aq(Eg water) = na+ (aq) + cl-(aq)

Question 7

Enthalpy change of hydration

Answer 7

The enthalpy change of hydration is the enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions

Eg Na+ (g) +aq = na+(aq)

Question 8

standard enthalpy change of reaction

Answer 8

The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states.

Question 9

Standard enthalpy change of combustion

Answer 9

The enthalpy that takes place when one mole of a substance reacts completely with oxygen under standard conditions with all reactants and products in their standard states.

Question 10

Enthalpy change of neutralisation

Answer 10

The energy change that accompanies the reaction of an acid by a base to form one mole of water under standard conditions