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Question 1

lattice enthalpy

Answer 1

enthalpy change when one mole of solid is formed by its gaseous ions (always large negative values - energy released)

Question 2

lattice enthalpy becomes more negative

Answer 2

for ions with greater charge density (increased ionic charge, decreased ionic radii)

ions with smaller radius can come closer together giving stronger ionic attraction, ions with higher charges have increased electrostatic interactions

increased electrostatic interaction = more energy released

Question 3

dissolving ionic substances

Answer 3

water molecules are polar and the charges on the molecules are attracted to the charges on the ions
form ion-dipole interactions
this causes ions to become separated from the lattice and be surrounded by water molecules
energy released from this interaction

Question 4

hydration enthalpy

Answer 4

enthalpy change for the formation of a solution of ions from one mole of gaseous ions (ALWAYS NEGATIVE - energy released)

Question 5

enthalpy change of solution =

Answer 5

enthalpy change of hydration of cation + enthalpy change of hydration of anion - lattice enthalpy

Question 6

if enthalpy change of solution is large and positive

Answer 6

a solute will not dissolve

Question 7

if enthalpy change of solution is negative

Answer 7

a solute will dissolve

Question 8

enthalpy change of solution

Answer 8

when one mole of a solute dissolves to form a dilute solution

Question 9

hydration enthalpy becomes more negative

Answer 9

for ions with greater charge density (increased ionic charge, decreased ionic radii)

small, highly charged ions can get close to water molecules and form stronger ion-dipole interactions

Question 10

dissolving ionic solids in non-polar solvents

Answer 10

ionic solids are insoluble in non-polar solvents
no positive/negative regions in solvent molecules so unable to interact strongly with ions
large +VE enthalpy change of solution

Question 11

strong intermolecular bonds in the solute generally indicates

Answer 11

more likely to dissolve

Question 12

greenhouse effect

Answer 12

1. radiation from the sun reaches the Earth, mainly consists of visible and UV radiation
2. Earth absorbs some of the solar radiation so warms up and emits IR
3. greenhouse gases such as CO2 and CH4 are present in troposphere and they absorb IR
4. vibrational energy of bonds increases and molecules in the atmosphere collide
5. kinetic energy of some molecules increases as energy is transferred between molecules
6. causes temperature of atmosphere to rise
7. greenhouse gases emit some of the absorbed radiation and some is also absorbed by the Earth

Question 13

increased concentrations of greenhouse gases leads to

Answer 13

an enhanced greenhouse effect

Question 14

IR window

Answer 14

wavelegth of IR that water vapour doesn’t absorb

CO2 absorbs IR at the same wavelength as IR window

Question 15

Bronsted-Lowry theory

Answer 15

states that an acid is a proton donor, and a base is a proton acceptor

Question 16

conjugate base

Answer 16

HA&raquo_space; A- + H+

(A-) behaves as a base in the presence of acid

Question 17

conjugate acid

Answer 17

HA&raquo_space; A- + H+

(HA) behaves as an acid in the presence of base

Question 18

water can act as

Answer 18

an acid or a base

Question 19

strong acids

Answer 19

easily and fully dissociate in water to form protons

Question 20

weak acids

Answer 20

have a weak tendency to dissociate to form protons, so only partially dissociate in solution

Question 21

assumptions when using acidity constant Ka equation for weak acids

Answer 21

[H+] = [A-]

equilibrium concentration of HA = initial concentration of HA in solution

Question 22

higher the pKa

Answer 22

weaker the acid

Question 23

buffers

Answer 23

solutions that can resist changes in pH, despite the addition of acids or alkali

Question 24

types of buffer:

Answer 24

weak acid and one of its salts

weak base and one of its salts

Question 25

assumptions with buffers

Answer 25

all the A- ions come from the salt
[the weak acid (HA) supplies very few A- ions in comparison with the fully ionised salt]

almost all the HA molecules of the weak acid remain unchanged

Question 26

adding acid to buffer

Answer 26

when protons are added, some A- ions from the salt react with the extra protons to form HA and water
this removes the added protons from the solution
pH is reestablished

Question 27

adding alkali to buffer

Answer 27

protons are removed from the solution
buffer solution counteracts this because protons can be regenerated from the acid HA
pH is reestablished

Question 28

Ka of buffers

Answer 28

= [H+] x [salt] / [acid]

Question 29

ratio of [salt] : [acid] in buffer

Answer 29

changing ratio from about 3:1 to about 1:3 alters the pH by roughly 1 unit
this is because it changes [H+] by a factor of about 9 or 10
(increase salt > [H+] lower > pH higher)

Question 30

Ksp

Answer 30

solubility product

if product of concentrations of ions is less than Ksp value then no precipitate will form

Question 31

entropy

Answer 31

measure of the number of ways of arranging molecules and distributing energy
entropy change = Joules per Kelvin per mole

Question 32

greater entropy

Answer 32

gas > liquid > solid
heavier larger atoms
more particles
straight compared with branched
energy levels closer together

Question 33

if entropy change of a process is

Answer 33

positive, reaction will occur spontaneously

negative, reaction is unlikely to occur spontaneously