Energetics (HL and SL)

Question 1

Ionisation Energy (IE)

Answer 1

The enthalpy change when one electron is removed from each atom in one mole of gaseous atoms

Question 2

Electron Affinity (EA)

Answer 2

The enthalpy change when one electron is added to each atom in one mole of gaseous atoms.
The 1st electron affinity is exothermic as it is favourable but the second is endothermic as the ion is negatively charged

Question 3

Lattice Enthalpy

Answer 3

The enthalpy change when one mole of ionic compound is broken apart into its constituent gaseous ions. It can be defined as either making or breaking the lattice and so can be endothermic or exothermic

Question 4

The effect of ion charge on lattice enthalpy

Answer 4

The higher the charge on the ion the higher the attraction within the lattice and the higher the lattice enthalpy.

Question 5

The effect of ion size on lattice enthalpy

Answer 5

The larger the ion the greater the internuclear distance and the smaller the attraction so the lower the lattice enthalpy.

Question 6

Enthalpy Change of Solution for Ionic Substances

Answer 6

This is calculated by taking the lattice enthalpy and adding it to the enthalpy change of solution for each ion but as they are exothermic:
lattice - hydration - hydration

Question 7

Specific Heat Capacity (of a pure substance)

Answer 7

The amount of heat needed to raise the temperature of 1g of that substance by 1 degree celsius

Question 8

Standard Enthalpy Change of Formation

Answer 8

The energy change upon the formation of 1 mol of a substance from its constituent elements in their standard state

Question 9

The Standard Enthalpy Change of Combustion

Answer 9

The heat evolved upon the complete combustion of 1 mol of that substance

Question 10

Entropy

Answer 10

It is a measure of the number of ways energy can be distributed within particles (given by S and has units in J/K)

Question 11

Changes in Entropy

Answer 11

Solids < liquids < gases

Question 12

S positive

Answer 12

Indicates an increase in entropy and so distribution of energy

Question 13

S negative

Answer 13

Indicates a decrease in entropy and so a decrease in the distribution of energy

Question 14

Calculating S

Answer 14

S products - S reactants

Question 15

S universe

Answer 15

The entropy of the universe must be increasing in order for the reaction to be spontaneous
S surroundings + S system
A spontaneous reaction does not have to occur quickly or frequently

Question 16

G (Gibbs free energy)

Answer 16

It must be negative for a spontaneous reaction

G = H -(TchangeinS/1000)

Question 17

Spontaneous at any temperature

Answer 17

H -

S +

Question 18

As temperature increases spontaneity increases

Answer 18

H +

S +

Question 19

As temperature increases spontaneity decreases

Answer 19

H -

S -

Question 20

Not spontaneous at any temperature

Answer 20

H +

S -