Year 13- Thermodynamics

Question 1

Enthalpy change of formation

Answer 1

Enthalpy change when 1 mole of
the compound is formed from its elements under standard conditions (298K and 100kpa), all
reactants and products being in their standard states

Question 2

Enthalpy of atomisation

Answer 2

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

Question 3

Enthalpy of sublimation

Answer 3

the enthpy change for a solid metal turning to gaseous atoms

numerically the same as the enthalpy of atomisation

Question 4

Bond association energy

Answer 4

the standard molar enthalpy change
when one mole of a covalent bond is broken into two gaseous
atoms (or free radicals

Question 5

First ionisation energy

Answer 5

the enthalpy change required to
remove 1 mole of electrons from 1 mole of gaseous atoms to form
1 mole of gaseous ions with a +1 charge

Question 6

Second ionisation energy

Answer 6

the enthalpy change to
remove 1 mole of electrons from one mole of gaseous 1+ ions
to produces one mole of gaseous 2+ ions.

Question 7

First electron affinity

Answer 7

the enthalpy change that occurs when 1
mole of gaseous atoms gain 1 mole of electrons to form 1 mole of
gaseous ions with a –1 charge

Question 8

Second electron affinity

Answer 8

s the enthalpy change when one
mole of gaseous 1- ions gains one electron per ion to produce
gaseous 2- ions

Question 9

Enthalpy of lattice formation

Answer 9

s the standard enthalpy change
when 1 mole of an ionic crystal lattice is formed from its
constituent ions in gaseous form.

Question 10

Enthalpy of lattice dissociation

Answer 10

the standard enthalpy
change when 1 mole of an ionic crystal lattice form is separated
into its constituent ions in gaseous form

Question 11

Enthalpy of hydration

Answer 11

Enthalpy change when one mole of gaseous ions become

aqueous ions

Question 12

Enthalpy of solution

Answer 12

the standard enthalpy change
when one mole of an ionic solid dissolves in a large enough
amount of water to ensure that the dissolved ions are well
separated and do not interact with one another

Question 13

What does the strength of enthalpy of lattice formation depend on?

Answer 13

the ion size and the ion charge

Question 14

How does the ion size affect enthalpy of lattice formation?

Answer 14

the larger the ions, the less negative it is as the charges become further apart and have a weaker attractive force between them

Question 15

How does the ion charge affect enthalpy of lattice formation?

Answer 15

the bigger the charge, the greater the attraction between ions so the enthalpy is stronger

Question 16

Down a group, what happens to the lattice enthalpies?

Answer 16

it becomes less negative

Question 17

What do theoretical lattice enthalpies assume?

Answer 17

a perfect ionic model where the ions are 100% ionic and the attractions are purely electrostatic

Question 18

Why is the theoretical lattice enthalpy not accurate?

Answer 18

because some compounds have some covalent character- it tends towards giant covalent so the lattice is stronger than it is if 100% ionic. this make the born-Haber value larger than the theoretical value.

Question 19

How does covalent character affect the difference between theoretical and experimental values?

Answer 19

the more the covalent character, the bigger the difference in values

Question 20

What makes a negative ion polarised?

Answer 20

when it becomes more covalent, the charge cloud is distorted.

Question 21

What is entropy?

Answer 21

a measure of disorder in a system

Question 22

Which one has a bigger jump in entropy- boiling or melting?

Answer 22

boiling

Question 23

What leads to a positive entropy change?

Answer 23

an increase in disorder

Question 24

What is the unit for entropy?

Answer 24

J K-1 mol-1

Question 25

Equation for entropy

Answer 25

sum of entropy of products- sum of entropy of reactant

Question 26

Equation for gibbs-free energy

Answer 26

∆G = ∆H - T∆S

Question 27

Units for gibbs-free energy

Answer 27

KJ mol-1

Question 28

When is gibbs-free energy negative?

Answer 28

when there is a spontaneous change

Question 29

What causes gibbs-free energy to be negative?

Answer 29

a reaction that has increasing entropy (positive) and is exothermic (-ve ∆H)

Question 30

Effect of temp on feasability

Answer 30

If ∆S is -ve, increasing temp makes it more likely that ∆G is negative

Question 31

What should ∆G be for a reaction to be feasible?

Answer 31

0 or negative

Question 32

How does the straight line equation apply to gibbs-free energy equation?

Answer 32

y=mx + c
c= ∆H
m= -∆S
x= T

Question 33

On a straight line graph, what does a positive gradient mean?

Answer 33

∆S is negative

Question 34

Enthalpies of solution- what happens when an ionic lattice dissolves in water?

Answer 34

bonds in the lattice are broken and new bonds are formed between the metal ions and water molecules

Question 35

Equation for enthalpy of solution

Answer 35

∆Hsolution =∆HL dissociation + sum of V hydH