Thermodynamics

Question 1

enthalpy change of formation

Answer 1

enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions

Question 2

lattice enthalpy of formation

Answer 2

enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions

Question 3

lattice enthalpy of dissociation

Answer 3

enthalpy change when 1 mole of a solid ionic compound is dissociated into its gaseous under standard conditions

Question 4

enthalpy change of dissociation

Answer 4

enthalpy change when 1 mole of bonds of the same type of molecule in the gaseous state is broken

Question 5

enthalpy change of 1st ionisation

Answer 5

enthalpy change when 1 mole of gaseous 1+ ions are made from 1 mole of gaseous atoms

Question 6

enthalpy change of atomisation

Answer 6

enthalpy change when 1 mole of gaseous atoms is made from an element in its standard states

Question 7

enthalpy change of 2nd ionisation

Answer 7

enthalpy change when gaseous 2+ ions are made from 1 mole of gaseous 1+ ions

Question 8

1st e- affinity

Answer 8

enthalpy change when 1mole of gaseous 1- ions is made from 1 mole of gaseous atoms

Question 9

2nd e- affinity

Answer 9

enthalpy change when 1 mole of gaseous 2- ions are made from 1 mole of gaseous 1- ions

Question 10

e.g. explain why the lattice dissociation enthalpy of magnesium chloride is greater than that of calcium oxide

Answer 10

-Mg ion is smaller
-attraction between ions is bigger

Question 11

enthalpy of solution =

Answer 11

ΔHsolution = ΔHL + ΣΔHhyd Mg2+ ions + ΣΔHhyd Cl−
ions

Question 12

Use your knowledge of bonding to explain why ∆Hϴ
is positive for this process

Answer 12

Hydrogen bonds between water molecules
1
Energy must be supplied in order to break (or loosen) them

Question 12

State the meaning of the symbol ϴ
in ∆Hϴ

Answer 12

standard pressure/conditions

Question 13

Give one reason why the
temperature of a sample of water can stay at a constant value of 0 °C when it
freezes

Answer 13

The heat given out escapes

Question 14

why is the electronegativity of fluorine greater than chlorine

Answer 14

-fluorine is smaller
-electrons are more attracted to nucleus

Question 15

e.g. Explain why the hydration enthalpy of the fluoride ion is more negative than the
hydration enthalpy of the chloride ion

Answer 15

-Fluoride (ions) smaller (than chloride) / have larger charge density
-So (negative charge) attracts (δ+ hydrogen on) water more strongly

Question 16

Suggest why the entropy change for dissolving silver fluoride in water has a
positive value.

Answer 16

-there is an increase in the number of particles

Question 17

What do lattice enthalpies help us determine?

Answer 17

The bigger the difference in lattice enthalpy , the more polarisation you have, the greater the covalent character