Topic 19- Thermodynamics

Question 1

Enthalpy of formation

Answer 1

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

Question 2

Mean bond enthalpy

Answer 2

The enthalpy change when one moles of covalent bonds is broken, with all species in the gaseous state, averaged over a range of different compounds.

Question 3

Enthalpy change of atomisation of an element

Answer 3

The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state

Question 4

Enthalpy change of atomisation of a compound

Answer 4

The enthalpy change when 1 mole of a compound in its standard state is converted to gaseous atoms

Question 5

First ionisation energy

Answer 5

The enthalpy change when 1 mole of gaeous 1+ ions is formed from 1 mole of gaseous atoms

Question 6

Second ionisation enthalpy

Answer 6

The enthalpy change when one mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions

Question 7

First electron affinity

Answer 7

The enthalpy change when 1 mole of gaseous 1- ions are formed from 1 mole of gaseous atoms

Question 8

Second electron affinity

Answer 8

The enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions

Question 9

Enthalpy change of hydration

Answer 9

The enthalpy change when water molecules surround one mole of gaseous ions

Question 10

Enthalpy of solution

Answer 10

The enthalpy change when 1 mole of an ionic solid dissolves completely in sufficient water to form a solution in which the ions are far enough apart not to interact with each other.

Question 11

Lattice enthalpy of formation

Answer 11

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

Question 12

Lattice enthalpy of dissociation

Answer 12

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

Question 13

Why do theoretical lattice enthalpies differ from experimental values

Answer 13

Due to covalent character

Question 14

What indicates how close a compound is to the perfect ionic structure?

Answer 14

The difference between experimental and theoretical lattice enthalpy values

Question 15

What indicates how close a compound is to the perfect ionic structure?

Answer 15

The difference between experimental and theoretical lattice enthalpy values

Question 16

When do substances tend to dissolve?

Answer 16

When it is neutral or exothermic

Question 17

When do substances tend to dissolve?

Answer 17

When enthalpy of solution is neutral or exothermic

Question 18

Equation to calculate entropy

Answer 18

Change in entropy= Entropy of products- Entropy og reactants

Question 19

Equation for free energy change

Answer 19

Delta G=Delta H-T *Delta S

Question 20

What are the units of free energy change?

Answer 20

J/mol

Question 21

Feasibility of reaction: Exothermic and positive entropy

Answer 21

Feasible at all temperatures

Question 22

Feasibility of reaction: Exothermic and negative entropy

Answer 22

Below certain temperatures

Question 23

Feasibility of reaction: Endothermic and positive entropy

Answer 23

Above certain temperatures

Question 24

Feasibility of reaction: Endothermic and negative entropy

Answer 24

Feasible at no temperatures

Question 25

Explain why enthalpy of hydration becomes less exothermic down group 1

Answer 25

Lower charge density down group
Attraction between partially negative oxygen and metal ion lower