Oceans

Question 1

How is the strength of ionic attraction measured?

Answer 1

Lattice enthalpy

Question 2

What is the lattice enthalpy?

Answer 2

Enthalpy change when one mole of solid is formed from its gaseous ions

Question 3

Are lattice enthalpies positive or negative, and why?

Answer 3

Negative- bond making

Question 4

How do you break down a lattice?

Answer 4

Put in energy equal to the negative LEH (this becomes positive as you are putting energy in)

Question 5

What factors affect lattice enthalpy?

Answer 5

Ionic charge
Ionic radii

Question 6

What makes a lattice enthalpy more negative?

Answer 6

Increased ionic charge
Decreased ionic radii

Charge density increases, and so increases attraction, increasing the bond strength

Question 7

Bond breaking/making

Answer 7

Breaking - endo +
Making - exo -

Question 8

How does hydration occur?

Answer 8

Ion-dipole interactions
Positive ions surrounded by negative end of water molecule
Negative ions surrounded by positive end of water molecule

Question 9

What does weak/extensive hydration mean?

Answer 9

Ions are weakly/strongly bound to water molecules

Question 10

How does charge density of an ion affect its hydration?

Answer 10

Larger charge density increases the number of water molecules it can attract
A small ion can become large as a hydrated ion

Question 11

How can energy be provided to break the lattice enthalpy?

Answer 11

Formation of bonds between ions and water molecules

Question 12

Why can’t hydration enthalpy be used to achieve enough energy to break a lattice?

Answer 12

Water molecules have strong hydrogen bonds, so breaking these bonds so they can reform around the ion also requires energy

Question 13

What is the enthalpy change of hydration?

Answer 13

Strength of attractions between ions and water molecules
Enthalpy change of a formation of solution from one mole of gaseous ions

Question 14

Lattice enthalpy of NaCl equation

Answer 14

Na+(g) + Cl-(g) –> NaCl(s)

Question 15

Hydration enthalpy of sodium equation

Answer 15

Na+(g) + aq –> Na+(aq)

Question 16

Is the value of hydration enthalpy negative or positive, and why?

Answer 16

Negative- hydration is exothermic as bonds are being formed

Question 17

What is enthalpy of solvation?

Answer 17

Using solvents other than water (eg ethanol)
Enthalpy change when 1 mol of ionic substance dissolves in the solvent to form a solution

Question 18

What is enthalpy change of solution?

Answer 18

Difference in enthalpy between
- hydration enthalpy
- lattice enthalpy
One mol of solute dissolves to form a very dilute solution

Question 19

What is the equation for enthalpy change of solution?

Answer 19

solutionH = hydH (cation) + hydH (anion) - leH

Question 20

Enthalpy cycle- what is the original and alternative route for solution enthalpy?

Answer 20

Original: ionic lattice + solvent –(solutionH)–> solution

Alternative: ionic lattice + solvent –(-leH)–> gaseous ions + solvent –(hydH of cation+anion)–> solution

Question 21

What does a negative enthalpy solution mean?

Answer 21

Hydration provides more energy than is needed to break the lattice
Solid will dissolve

Question 22

What does a positive enthalpy of solution mean?

Answer 22

Hydration does not provide as much energy as is needed to break up the lattice
Solute does not dissolve

Question 23

What does a slightly positive enthalpy of solution mean?

Answer 23

Hydration doesn’t provide exact energy but solute still dissolves

Question 24

What are examples of greenhouse gases and where are they found?

Answer 24

CO2 and methane
Troposphere

Question 25

What 2 things occur when IR is absorbed by greenhouse gases?

Answer 25

1) Increases vibrational energy of gases; vibrational energy can be transferred to other molecules by collision; increases kinetic energy- raising temp of air 2) Some IR re-emitted to earth, some to space

Question 26

What is the most abundant greenhouse gas in the atmosphere?

Answer 26

Water vapour

Question 27

What is the IR window?

Answer 27

The wavelengths of IR that water vapour does not absorb

Question 28

Which gas absorbs wavelengths of light in the IR window?

Answer 28

CO2

Question 29

How is the temperature of the earth being increased by increasing levels of CO2?

Answer 29

More CO2 More wavelengths of IR window absorbed- increasing temp Increasing temp = more water vapour

Question 30

What is an acid?

Answer 30

H+/proton donor

Question 31

What is a base?

Answer 31

H+/proton acceptor

Question 32

What is a conjugate acid-base pair?

Answer 32

HA (conj. acid) --> H+ + A- (conj. base)

Question 33

Water acting as a base

Answer 33

HCl + H2O --> H3O+ + Cl-

Question 34

Water acting as an acid

Answer 34

H2O + NH3 --> OH- + NH4+

Question 35

What is the equation for pH?

Answer 35

-log10 [H+(aq)]

Question 36

What is a strong acid?

Answer 36

Strong tendency to donate H+ Dissociate completely in aq

Question 37

Equations for dissociation of a strong acid

Answer 37

HA + H2O --> H3O+ + A- Water is in excess: HA --> H+ + A-

Question 38

Examples of strong acids

Answer 38

HCl H2SO4

Question 39

What is a weak acid?

Answer 39

Tendency to donate H+ is weaker Does not dissociate completely in water

Question 40

Equation for weak acids

Answer 40

HA <--> H+ + A-

Question 41

Example of a weak acid

Answer 41

Ethanoic acid (CH3COOH)

Question 42

Equilibrium in terms of strength of acid

Answer 42

Weak = left Strong = right

Question 43

How to calculate pH of a strong acid

Answer 43

pH = -log10 [H+]

Question 44

How to calculate [H+] of a strong acid

Answer 44

10^-pH

Question 45

How to calculate pH of a weak acid

Answer 45

Ka = [H+][A-] / [HA]

Question 46

What are the 2 assumptions made about [H+] of weak acids?

Answer 46

1) [H+] = [A-] Water is another source of [H+] Produces far fewer H+ than a weak acid, neglecting ionisation of water has no effect 2) Amount of HA at equilibrium = amount of HA put into solution Neglect H+ lost as weak acids dissociate very little

Question 47

pKa equation

Answer 47

pKa = -log10 Ka

Question 48

What is pKa?

Answer 48

Logarithmic scale as values for Ka of weak acids is very small

Question 49

How do you calculate pH of strong alkali?

Answer 49

1) Equation 2) Ka equation 3) Kw equation

Question 50

pH of strong alkali- equation (1)

Answer 50

H2O <--> H+ + OH-

Question 51

pH of strong alkali- Ka equation (2)

Answer 51

Ka = [H+][OH-] / [H2O]

Question 52

pH of strong alkali- Kw equation (3)

Answer 52

Water is in excess Kw = [H+][OH-]

Question 53

What is a buffer?

Answer 53

Solutions that resist changes in pH despite the addition of small quantities of acid/alkali

Question 54

What are buffer solutions made from? Examples

Answer 54

A weak acid/base and one of its salts Ethanoic acid + sodium ethanoate Ammonia + ammonium chloride

Question 55

Equation for action of a buffer solution

Answer 55

HA <--> H+ + A-

Question 56

What are the assumptions made about buffers to explain why they resist changes in pH?

Answer 56

1) All A- comes from the salt Weak acid supplies very few A- in comparison to salt 2) Almost all HA remains unchanged

Question 57

What happens when H+ is added to a buffer solution?

Answer 57

A- reacts with extra H+ Forms HA and water Removes H+ Reestablish pH

Question 58

What happens when OH- is added to a buffer solution?

Answer 58

H+ removed by OH- H+ regenerated by HA

Question 59

Buffer calculation equation

Answer 59

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

Question 60

What can be used to measure 'insoluble' ionic solids?

Answer 60

Kc - equilibrium constant

Question 61

Why is equilibrium equation different for 'insoluble' ionic solids?

Answer 61

Adding more solid does not cause equilibrium to shift towards product Solution is saturated at that temp Doesn't affect amount of solid present Solubility product equation

Question 62

What is the solubility product equation?

Answer 62

Ksp (solid) = [+][-]

Question 63

What is the solubility product constant?

Answer 63

Conditions for equilibrium between sparingly soluble solid + saturated solution

Question 64

Using Ksp to predict if a precipitate will form

Answer 64

[+][-] = more than Ksp = will precipitate [+][-] = less or equal to Ksp = ions stay in solution

Question 65

What is entropy?

Answer 65

Randomness of a system, mathematically calculated Ways that energy can be arranged between particles

Question 66

What does +/- entropy mean?

Answer 66

Positive = products more disordered than reactants Negative = reactants more disordered than products

Question 67

What are the units for entropy?

Answer 67

J K-1mol-1

Question 68

What causes a higher entropy?

Answer 68

More spread out molecules Energy shared among more molecules

Question 69

How to predict if a change is feasible?

Answer 69

TotalS must be positive

Question 70

What is the equation for total entropy change?

Answer 70

TotalS = sysS - surrS

Question 71

How do you calculate entropy of a system?

Answer 71

Entropy of products - entropy of reactants

Question 72

What is the equation for surrS?

Answer 72

-ΔH/T