Energetics

Question 1

Define the standard enthalpy change of combustion.

Answer 1

The energy evolved (-) when ONE mole of the substance is COMPLETELY burnt in oxygen under standard conditions.

Question 2

Define the standard enthalpy change of neutralisation.

Answer 2

The energy evolved (-) when ONE mole of WATER is formed from the neutralisation between acid and base under standard conditions.

Question 3

Define the standard enthalpy change of formation.

Answer 3

The energy change (+/-) when ONE mole of substance is formed from its constituent ELEMENTS under standard conditions.

Question 4

Define bond energy.

Answer 4

It is the average energy absorbed (+) to break ONE mole of X-Y covalent bonds (state explicitly in context of qn) in the GASEOUS STATE to form GASEOUS atoms under standard conditions.

Question 5

Define Lattice energy.

Answer 5

The energy evolved (-) when ONE mole of the solid ionic compound is formed from its constituent GASEOUS IONS under standard conditions.

Question 6

Define the standard enthalpy change of atomisation.

Answer 6

The energy absorbed (+) when ONE mole of GASEOUS ATOMS is formed from the element under standard conditions.

Question 7

Define 1st I.E.

Answer 7

The energy absorbed (+) to remove ONE mole of electrons from ONE mole of gaseous atoms to form ONE mole of singly positively charged gaseous ions.
[note: even for non-metals]

Question 8

Define 2nd I.E.

Answer 8

The energy absorbed (+) to remove ONE mole of electrons from ONE mole of singly positively charged ions to form ONE mole of doubly positively charged gaseous ions.
[note: even for non-metals]

Question 9

Define first electron affinity.

Answer 9

The energy evolved (-) when ONE mole gaseous atoms acquires ONE mole of electrons to give ONE mole of singly negatively charged gaseous ions.

Question 10

Define the standard enthalpy change of hydration.

Answer 10

The energy evolved (-) when one mole of GASEOUS IONS is hydrated under standard conditions.

Question 11

Define standard enthalpy change of solution.

Answer 11

The energy change (+/-) when one mole of the substance is completely dissolved in a solvent to form an infinitely dilute solution under standard conditions.

Question 12

Define entropy (S) and state its units.

Answer 12

Entropy measures the degree of disorder in a system.
Units: J K-1 mol-1

Question 13

What are the “standard conditions”?

Answer 13

298K and 1 bar.

Question 14

What are the units for Gibbs free energy?

Answer 14

J mol-1
(or kJ mol-1)