Thermodynamics

Question 1

Define enthalpy change

Answer 1

Heat energy transferred in a reaction at constant pressure

Question 2

Define enthalpy change of formation

Answer 2

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

Question 3

Define bond dissociation enthalpy

Answer 3

Enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken

Question 4

Define enthalpy change of atomisation of an element

Answer 4

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

Question 5

Define enthalpy change of atomisation of a compound

Answer 5

Enthalpy change when 1 mole of a compound is converted to gaseous atoms under standard states

Question 6

Define first ionisation energy

Answer 6

Enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms

Question 7

Define second ionisation energy

Answer 7

Enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of 1+ gaseous atoms

Question 8

Define electron affinity

Answer 8

Enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms

Question 9

Define second electron affinity

Answer 9

Enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of 1- gaseous atoms

Question 10

Define enthalpy change of hydration

Answer 10

Enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions

Question 11

Define enthalpy change of solution

Answer 11

Enthalpy change when 1 mole of solute is dissolved in enough solvent that no further enthalpy change occurs on furthur dilution

Question 12

Define lattice enthalpy of formation

Answer 12

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

Question 13

Define lattice enthalpy of dissociation

Answer 13

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

Question 14

What does the purely ionic lattice assume?

Answer 14

• All ions are spherical
• Evenly distributed charge
• No covelant character

Question 15

What does it mean when the difference btw experimental + theoretical lattice enthalpy are big?

Answer 15

• Bonding is stronger than ionic model predicts
• Bonds are strongly polarised + have a lot of covelant character

Question 16

What does it mean when the difference btw experimental + theoretical lattice enthalpy are small?

Answer 16

Close to being purely ionic

Question 17

When a solid ionic lattice dissolves in water, what are the 2 things that happen?

Answer 17

• Bonds btw ions break to give free ions - endo
• Bonds btw ions + water are made - exo

Question 18

When can substances only dissolve?

Answer 18

If energy released is roughly the same, or greater than the energy taken in

Question 19

Define entropy

Answer 19

Measure of the no. ways that particles can be arranged + no. ways that energy can be shared out btw the particles

Question 20

Large positive entropy

Answer 20

High level of disorder

Question 21

What affects entropy?

Answer 21

• Physical state - gas has highest entropy
• No. particles - more particles = entropy inc

Question 22

Why do particles move to increase their entropy?

Answer 22

More energetically stable when theres more disorder

Question 23

For a reaction to be feasible it must be..

Answer 23

-ve