Energetics

Question 1

Entropy:

Answer 1

measure of disorderliness in the system (no of ways which matter can be arranged and energy can be distributed in a system)

Question 2

Standard enthalpy change of reaction, Δ𝑯𝒓
ꝋ

Answer 2

The standard enthalpy change of reaction is the energy change when molar quantities of reactants
as stated in the balanced stoichiometric equation react together at 298 K and 1 bar

Question 3

Standard enthalpy change of formation, Δ𝑯𝒇
ꝋ

Answer 3

The standard enthalpy change of formation is the energy change when one mole of a substance is
formed from its constituent elements in their standard states at 298 K and 1 bar.

Question 4

Standard enthalpy change of combustion, Δ𝑯𝒄
ꝋ

Answer 4

The standard enthalpy change of combustion is the energy released when one mole of a substance
is completely burnt in excess oxygen at 298 K and 1 bar.

Question 5

Standard enthalpy change of neutralisation, Δ𝑯𝒏
ꝋ

Answer 5

The standard enthalpy change of neutralisation is the energy released when one mole of water is
formed from the reaction between an acid and an alkali at 298 K and 1 bar.

Question 6

Standard Enthalpy Change of atomisation, Δ𝑯𝒂𝒕
ꝋ

Answer 6

The standard enthalpy change of atomisation is the energy absorbed when one mole of gaseous
atoms is formed from its element in its standard state at 298 K and 1 bar.

Question 7

Bond energy

Answer 7

Bond energy is the energy absorbed to break one mole of covalent bonds between two atoms in
gaseous molecules to form state to form gaseous atoms.

Question 8

First ionisation energy

Answer 8

First ionisation energy (1st I.E.) of an element is the energy absorbed to remove one mole of valence
electrons from one mole of gaseous atoms to form one mole of gaseous single positively charged
cations.

Question 9

First electron affinity

Answer 9

First electron affinity (1st E.A.) of an element is the energy released when one mole of gaseous
atoms gain one mole of electrons to form one mole of gaseous single negatively charged anions.

Question 10

Second electron affinity

Answer 10

Second electron affinity (2nd E.A.) of an element is the energy change when one mole of gaseous
single negatively charged anions gain one mole of electrons to form one mole of gaseous double
negatively charged anions.

Question 11

Lattice Energy, L.E., of an ionic compound

Answer 11

Lattice energy (L.E.) of an ionic compound is the energy released when one mole of ionic solid is
formed from its constituent gaseous ions.

Question 12

Standard Enthalpy Change of hydration, Δ𝑯𝒉𝒚𝒅
ꝋ

Answer 12

The standard enthalpy change of hydration is the energy released when one mole of gaseous ions
is hydrated at 298 K and 1 bar.

Question 13

Standard enthalpy change of solution, Δ𝑯𝒔𝒐𝒍
ꝋ

Answer 13

The standard enthalpy change of solution is the energy change when one mole of substance is
completely dissolved in a solvent to form an infinitely dilute solution at 298 K and 1 bar.