Energetics 2

Question 1

Lattice energy

Answer 1

The energy change when one mole of an ionic solid is formed from its gaseous ions

Question 2

Atomisation energy

Answer 2

The energy change for the formation of one mole of gaseous atoms from an element in its standard state at 298K and 100kPa
Eg 1/2Br2(l)=>Br-(g)

Question 3

Electron affinity

Answer 3

First electron affinity is the energy change for the addition of one electron for each mole of atoms in the gas phase

Question 4

Second electron affinity

Answer 4

Energy change for the addition of one electron for each mole of ions with a negative charge in the gas phase

Question 5

Lattice energy provides a measure of

Answer 5

Ionic bond strength

Always exothermic as is the energy of bonds being made

Question 6

Experimental lattice energy value is

Answer 6

From a born-Haber cycle

Question 7

Theoretical lattice energy value is

Answer 7

Obtained from electrostatic theory
Based on: ionic charges and ionic radii
Assumes perfect ionic bonding

Question 8

Comparing experimental and theoretical lattice energy values indicates

Answer 8

The degree of covalent bonding

Possible covalent character?

Question 9

Polarising power

Answer 9

Based on the strength of the pull of cations on the electrons and how much the anion allows the electrons to be pulled

Question 10

Factors that increase polarisation in ionic compound are

Answer 10

• increased charge on anion or cation
• increased size of anion
• decreased size of cation

Question 11

The greater the polarisation effect on covalent character

Answer 11

The greater the covalent character

Question 12

Hydration of ions

Answer 12

When ionic substances in water, polar water highly attracted to ions
The process of water molecules linking to ions
Water molecules are vibrating, s as they bond to the ions they the ions free from the lattice

Question 13

Enthalpy of hydration

Answer 13

Heat energy change when one mole of gaseous ions dissolve in an excess of water to form an infinitely dilute solution under standard conditions

Question 14

Enthalpy of solution

Answer 14

Heat energy change when one mole of ionic solid dissolved in excess water in standard conditions

Question 15

Enthalpy of hydration is affected by

Answer 15

Ionic radii
Ionic charges
Greater attraction more energy released

Question 16

Entropy

Answer 16

Measure of the disorder of a system and that the natural direction of change is increasing total entropy

Question 17

Entropy change of a system =

Answer 17

Entropy change of products - entropy change of reactants

Question 18

Entropy change of surroundings =

Answer 18

• enthalpy / temperature

Question 19

Total Entropy change =

Answer 19

Entropy change of systems + entropy change of surroundings

Question 20

2nd law of thermodynamics

Answer 20

For a reaction to be feasible at a given temperature total entropy change > 0

Question 21

Entropy changes occur during

Answer 21

• changes of state
• dissolving of a solid ionic lattice
• reactions where there is a change in the number of moles from reactants to products

Question 22

Gibbs free energy change

Answer 22

Enthalpy - (temperature x entropy change of system) < 0 to be feasible

Question 23

Gibbs at equilibrium =

Answer 23

-R x T x lnK