Energetics 5.3/15.1

Question 1

Average bond enthalpy

Answer 1

The energy needed to break one mol of a bond in a gaseous molecule under standard conditions averaged over similar compounds.

Question 2

▲H using Average bond enthalpy

Answer 2

Sum of bonds broken - Sum of bonds formed

Question 3

Bond Enthalpy

Answer 3

The energy needed to break one mol of a bond in a gaseous molecule under standard conditions

Question 4

Formula for energy of photon

Answer 4

E = hf = hc/λ

Ephoton. 1 photon breaks 1 bond

Question 5

Free radical

Answer 5

Specie with an unpaired electron

Question 6

1st Ionization energy

Answer 6

minimum energy required to remove 1 mole of electrons from 1 mole of gaseous atoms.
1) Since ionization always requires energy, it is
always endothermic.

Question 7

1st electron affinity

Answer 7

Enthalpy change when 1 mole of gaseous electrons is added to 1 mole o gaseous atoms.
1) . This process can be both exothermic and endothermic
depending on if it is the first e.a or higher degree of e.a.

Question 8

Lattice enthalpy

Answer 8

Enthalpy change that occurs when 1 mole of a solid ionic compound is separated into gaseous ions under standard conditions

Question 9

Enthalpy change of atomization

Answer 9

Enthalpy change when 1 mole of gaseous atoms is formed from the elements in its standard state.

Question 10

Born Haber’s Cycle

Answer 10

Energy cycle for the formation of an ionic compound

Question 11

ΔHlat° formula

Answer 11

ΔHlat° = -ΔHf° + the rest =

Question 12

Factors that affect lattice enthalpy

Answer 12

1) Charge on the ion

2) Radius of the ion

Question 13

Enthalpy of solution

Answer 13

Enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution

Question 14

Enthalpy of hydration

Answer 14

Enthalpy change when 1 mole of a gaseous ion dissolve in water to give a solution of infinite dilution
1) Always negative

Question 15

Formula for ▲H(sol)

Answer 15

Enthalpy of solution is just the enthalpy of two things
1. Enthalpy of lattice, to break the lattice:
NaCl (s) → Na+ (g) + Cl-
(g)
2. Enthalpy of hydration, to literally hydrate the ions to aqueous solutions.
Na+ (g) + Cl-
(g) → Na+ (aq) + Cl-
(aq)
Putting these together using Hess’s law will indeed give us the enthalpy of solution which is:
NaCl (s) → Na+ (aq) + Cl-
(aq)
To put more generally:
ΔHsol° = ΔHlat° + ΔHhyd° of ion1 + ΔHhyd° of ion2

▲H(sol)= ▲H(hydration)+▲H(Lattice enthalpy)

Question 16

Factors that affect enthalpy of hydration

Answer 16

Determined by the attraction between ions and the water molecules.

1) Size of the ion
2) Charge on the ion