module 5.2 - physical chemistry and transition elements: energy

Question 1

lattice enthalpy definition

Answer 1

enthalpy change when 1 mol of an ionic compound is formed from its gaseous ions under standard conditions

Question 2

what is lattice enthalpy a measure of

Answer 2

energy released when forming an ionic bond in a giant ionic lattice

Question 3

enthalpy change of atomisation

Answer 3

enthalpy change when 1 mol of gaseous atoms is formed from the elements in its standard state under standard conditions

Question 4

electron affinity

Answer 4

enthalpy change when 1 electron is added to each atom in 1 mol of gaseous atoms to form 1 mol of gaseous negative ions under standard conditions

Question 5

enthalpy change of formation

Answer 5

enthalpy change when 1 mol of a compound is formed from its elements under standard conditions

Question 6

first ionisation energy definition

Answer 6

the energy required to remove 1 mol of electrons from 1 mol of atoms of an element in the gaseous state to form 1 mol of gaseous ions.

Question 7

why can’t we use Hess’ Law to measure lattice enthalpy

Answer 7

cause we can’t measure lattice enthalpy directly so we do it indirectly

Question 8

what do we use to measure lattice enthalpy

Answer 8

Born Haber cycle

Question 9

enthalpy change of solution

Answer 9

enthalpy change when 1 mol of a solute dissolves into a solvent under standard conditions

Question 10

enthalpy change of hydration

Answer 10

enthalpy change when 1 mol of gaseous ions are hydrated to form 1 mol of aqueous ions

Question 11

entropy definition

Answer 11

measure of the dispersal of energy in a system

Question 12

greater entropy =

Answer 12

greater dispersal of energy = greater disorder

Question 13

difference in entropy between states of matter

Answer 13

gas > liquid > solid

Question 14

calculation for entropy change in a system

Answer 14

∆S⦵ = ∑S⦵ (products) - ∑S⦵ (reactants)

Question 15

what must happen in a reaction for it to be deemed feasible

Answer 15

• must occur spontaneously

Question 16

what must decrease in order for a reaction to be feasible

Answer 16

gibb’s free energy

Question 17

equation to calculate free energy change

Answer 17

∆G = ∆H - T∆S

Question 18

unit of measure for ∆G

Answer 18

KJ mol-1

Question 19

unit of measure for ∆H

Answer 19

KJ mol-1

Question 20

unit of measure for T

Answer 20

kelvin (+273)

Question 21

unit of measure for ∆S

Answer 21

Jmol-1K-1 (divide by 1000)

Question 22

what must the value of ∆G be for the reaction to be feasible

Answer 22

∆G has to be a negative value (∆G < 0)

Question 23

limitations of using ∆G

Answer 23

• just because the reaction is feasible doesn’t mean it will occur at an observable rate
• while ∆G can be used to determine the feasibility of a reaction, it does not take into account the kinetics of the reaction i.e rate of reaction
• some reactions are feasible but very slow