3.6 enthalpy

Question 1

what is conservation of energy

Answer 1

energy is neither created nor destroyed but changed from one form to another

Question 2

what are standard conditions?

Answer 2

298k
1atm

Question 3

enthalpy of formation(^hf):

Answer 3

• exothermic
• enthalpy change when one one mole of a substance is formed from its elements in their standard states

Question 4

enthalpy of combustion(^Hc):

Answer 4

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

Question 5

Ionisation enthalpy (^Hie) first:

Answer 5

• endothermic
• enthalpy change when one mole of gaseous atoms loses one electron per atom to produce gaseous 1+ ions.
  e.g: Na(g) ———-> Na+(g) + e-

Question 6

Ionisation enthalpy second:

Answer 6

when one mole of gaseous 2+ ions is produced from one mole of 1+ ions.

Question 7

electron affinity first:

Answer 7

• exothermic
• produces 1 mole of gaseous ions with a -1 charge
  cl(g) + e- -> cl-(g)

Question 8

electron affinity second:

Answer 8

• endothermic
• when one mole of gaseous 1- ions gains one electron to produce gaseous 2- ions.

Question 9

enthalpy of atomisation(^Hat):
(solids and gases)

Answer 9

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

Question 10

Hydration enthalpy:

Answer 10

• exothermic
• producing 1 mole of aq ions from one mole of gaseous ions

Question 11

enthalpy of solution:

Answer 11

when an ionic solid dissolves producing an aqueous solution.

Nacl(s) + aq ——> Na+(aq) + cl- (aq)

Question 12

Lattice enthalpy of formation:

Answer 12

• exothermic
• when 1 mole of an ionic compound is formed from its gaseous ions

Question 13

Lattice breaking:

Answer 13

• endothermic
• breaking 1 mole of an ionic compound into its gaseous ions