Thermodynamics

Question 1

enthalpy of 1st ionisation energy

Answer 1

• enthalpy change when one mole of gaseous atoms LOSES 1 mole of electrons,
• to form 1 mole of gaseous 1+ ions

Question 2

enthalpy of atomisation

Answer 2

enthalpy change when 1 mole of gaseous ions are formed from 1 mole of an element in its standard state

Question 3

enthalpy of 1st electron affinity

Answer 3

• enthalpy change when 1 mole of gaseous atoms GAINS 1 mole of electrons
• to form 1 mole of gaseous -1 ions

Question 4

lattice enthalpy of formation / lattice enthalpy

Answer 4

enthalpy change when 1 mole of an ionic compound is FORMED from its constituent ions in their gaseous state, under standard conditions

Question 5

lattice enthalpy of dissociation

Answer 5

enthalpy change when 1 mole of an ionic compound is BROKEN DOWN into its constituent ions in their gaseous state

Question 6

enthalpy of solution

Answer 6

standard enthalpy change when 1 mole of a solute is DISSOLVED to form aqueous ions

Question 7

enthalpy of hydration

Answer 7

standard enthalpy change when 1 mole of gaseous ions forms 1 mole of aqueous ions

Question 8

bond enthalpy / bond disassociation enthalpy

Answer 8

enthalpy change when 1 mole of identical bonds in the gaseous state are broken

Question 9

enthalpy change of formation

Answer 9

enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions

Question 10

Suggest why 2nd electron affinity is an endothermic process. (2mk)

Answer 10

• The negative X- ion
• repels the electron being added

Question 11

Perfect ionic model assumes…

Answer 11

• all ions are perfectly spheres (no polarisation)
• all bonds are 100% ionic (no covalent character)
• attractions are purely electrostatic
• all ions have an even charge distribution

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Question 12

Explain why theoretical enthalpy is different than the experimental value of a BHC.

Answer 12

• experimental lattice enthalpy value include some degree of covalent character (allows for covalent interaction)
• theoretical lattice assumes ONLY ionic interaction

Question 13

What is needed for a substance to dissolve?

Answer 13

• substance bonds must break (endothermic)
• new bonds formed between the solvent and the substance (exothermic)

Question 14

Explain why a reaction, which is calculated to be feasible ( ΔG = 0), may not be observed to occur.

Answer 14

• activation energy too high
• rate of reaction is too slow

Question 15

Suggest why 1st electron affinity has a negative value.

Answer 15

• there is an attraction between the nucleus and the added electron
• energy is released when the electron is gained