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Advanced Higher Chemistry > Last Minute Cram - Physical > Flashcards

Last Minute Cram - Physical Flashcards

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1
Q

equilibrium is…

A
  1. a reaction where the rate of the forward reaction is equal to the rate of the reverse.
  2. where concentration of the reactants and products are constant.
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2
Q

factors which affect equilibrium

A

temperature
pressure
concentration

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3
Q

factors not affecting equilibrium

A

catalyst

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4
Q

what are stoichiometric coefficients?

A

molar ratios

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5
Q

to determine equilibrium composition of a mixture, you need…

A

equilibrium amount of only one of the species

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6
Q

what is the equilibrium constant (K)?

A

a value used to characterise the composition of the reaction mixture.

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7
Q

there are several forms of the equilibrium constant which all vary with what?

A

temperature

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8
Q

Kc

A

the equilibrium values are expressed as concentration of mol/L

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9
Q

Kp

A

the equilibrium values are expressed as partial pressures (used for reactions involving gases)

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10
Q

equilibrium law

A

expression of the amounts of products and reactants in an equilibrium.

Kc = [products]^p / [reactants]^r

at a constant temperature

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11
Q

what is the value of Kc affected by?

A

a change in temperature

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12
Q

what is the value of Kc not affected by?

A
  • a change in concentration of reactants or products
  • a change in pressure
  • adding a catalyst
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13
Q

heterogeneous reaction

A

where the reactants are in different states.

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14
Q

homogeneous reaction

A

where the reactants are in the same state.

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15
Q

what do you not include in the equilibrium expression?

A

any term for a solid because any pure solid is given a constant of 1.

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16
Q

if using partial pressures, what is different about the equilibrium expression?

A

Big ‘P’ instead of square brakcets

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17
Q

will the values of Kp and Kc be the same or different in general?

A

different

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18
Q

to obtain a high K value…

A

you would have to have a top heavy equation so there are more products.

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19
Q

to obtain a low K value…

A

you would have to have a bottom heavy equation and therefore reactants would be favoured.

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20
Q

If the value of K is around 1…

A

neither products or reactants are favoured.

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21
Q

what change does concentration have on eqm position and K value?

A

EQM position changes

No change to value of K

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22
Q

what change does pressure have on eqm position and K value?

A

EQM position changes

No change to value of K

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23
Q

what change does temperature have on eqm position and K value?

A

EQM position changes

K value changes

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24
Q

what change does a catalyst have on eqm position and K value?

A

No change to EQM position

No change to K value

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25
Q

If a solute is added to two immiscible liquids and the solute is soluble in both…

A

Some of the solute will dissolve in each of the solvents.

When the solute is shaken the solute distributes itself between the two liquids in a definite ratio called the partition coefficient.

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26
Q

partition/distribution coefficient is…

A

called K and has no units and is temperature dependant.

both concs need same units

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27
Q

you will get more efficient extraction if…

A

you do more than one extraction and use smaller volumes.

eg: 4x5 is better than 2x10 or 1x20

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28
Q

chromatography works providing…

A

the partition coefficients are different.

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29
Q

chromatography relies on…

A

a mobile phase and stationary phase

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30
Q

Rf value

A

the distance that the component has travelled compared to the distance the solvent has travelled (solvent front)

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31
Q

what can be done to ensure Rf value stays constant?

A

is all conditions are reproduced exactly i.e. type of paper, solvent and temperature

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32
Q

Rf=

A

distance travelled by the component / distance travelled by the solvent

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33
Q

gas liquid chromatography

A

mobile phase = gas
stationary phase = liquid held on an inert solid support of relatively small particle size
stationary phase in column (usually coiled and placed in oven)
carrier gas comes out column, passes into detector which measures changes to composition of gas

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34
Q

suitable gas to use as a mobile phase

A

inert (non-reactive)

eg: helium

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35
Q

hydronium ion

A

H3O+

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36
Q

acid

A

any substance capable of donating a proton

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37
Q

base

A

any substance capable of accepting a proton

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38
Q

In Bronsted-Lowry terms, the ionisation of water is represented by:

A

H20 + H20 –> H30+ + OH-

acid + base–>conjugate acid + conjugate base

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39
Q

conjugate acid

A

comes from the base
acts as an acid

the species formed when a base accepts a proton

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40
Q

conjugate base

A

comes from the acid
acts as a base

the species left when an acid donates a proton

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41
Q

when an acid donates a proton, the species left is called the…

A

conjugate base of that acid

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42
Q

when a base accepts a proton the species formed is called the…

A

conjugate acid of that base

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43
Q

the number of H+ and OH- ions in water are…

A

equal

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44
Q

Kw at 25 degrees

A

1x10^-14

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45
Q

H20 –> H+ + OH-

exo or endo?

A

endo

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46
Q

H20 –> H+ + OH-

increase/ decrease in temp

A

increase - eqm moves to right

decrease - moves to left

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47
Q

pH equations

A

pH=-log[H+]

[H+]=10^-pH

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48
Q

pH + p0H =

A

14

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49
Q

the strength of an acid is determined by…

A

the extent to which it ionises

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50
Q

strong acids

A

completely ionise in aqueous solutions

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51
Q

strong bases

A

completely dissociate into ions in aqueous solutions

52
Q

examples of strong acids

A

HCl
HNO3
H2S04

most other acids are weak

53
Q

examples of strong bases

A

NaOH
KOH
Ca(OH)2

most other bases are weak

54
Q

weak acid

A

an acid that only slightly dissociates in a water solution

only a small percent of acid molecules donate their hydrogen

55
Q

example of weak acid

A

ethanoic acid

CH3COOH (5% ionisation @25 degrees)

56
Q

weak bases

A

most bases are weak

only dissociate slightly in water solution

57
Q

example of weak base

A

NH3

58
Q

Ka equation

A

Ka=[H30+][A-] / [HA]

Ka=[H+]^2 / [C]

measure of the strength of an acid

59
Q

Ka values of the strongest weak acids

A

10^-4

1 in every 10000 molecules break up to form ions

60
Q

equations to link pKa and Ka

A

pKa=-logKa

Ka=10^-pKa

61
Q

calculating pH from the pKa

A

pH=1/2pKa-1/2logc

62
Q

dissiciation of any base B in aqueous solutions can be represented by the equation…

A

B+H20–>BH+ + OH-

hydrogen ion transferred from water to the base

63
Q

dissociation constant of B

A

the dissociation constant Ka of the conjugate acid BH+

64
Q

relating Ka and Kb

A

Ka=10^-14/Kb

KaxKb=10^-14

65
Q

what does the ka value of the conjugate acid gove information about?

A

the strength of the base

66
Q

what happens to the base as the value of Ka increases?

A

base gets weaker

67
Q

what happens to the base as the value of Ka decreases?

A

base gets stronger

68
Q

what are salts?

A

ionic compounds that return from the neutralisation reaction of an acid and a base

69
Q

soluble salts will dissociate in solution to form…

A

ions

70
Q

why do some salts dissolve to form acidic/alkaline solutions?

A

due to the ability for the ions within the solution to dissociate

strong acids/bases fully dissociate
weak acids/bases only partially dissociate

71
Q

what salt will form when a strong acid and base dissolve?

A

pH7

fully dissociate

72
Q

what salt will form when a weak acid and strong base dissolve?

A

alkaline solution

73
Q

what salt will form when a strong acid and weak base dissolve?

A

acidic solution

74
Q

why do H+ and Cl- have no tendency to join but NH4+ and OH- do?

A

HCl is a strong acid so will fully dissociate

NH4+ are ions of a weak base and will associate with OH-

75
Q

what are indicators used for?

A

to determine the end-point in an acid-alkali titration

76
Q

what are indicators?

A

dyes whose colours are sensitive to pH

usually a weak acid

77
Q

dissociation of an indicator (weak acid)

A

HIn + H2O –> H3O+ + In-

78
Q

“choose a suitable indicator” question

A

use table in data booklet

make sure it covers the correct pH range

79
Q

theoretical point for an indicator colour change

A

[HIn] = [In-]

and therefore Kin=[H3O+]

i.e. pKin=-log[Kin] (pKin=pH)

80
Q

In practice point for indicator colour change

A

colour change is only distinguishable when [HIn] and [In-] differ by a factor of 10

pH=pKin +/- 1
(log10=1)

81
Q

when is a suitable indicator not able to be chosen?

A

weak acid and weak alkali since the pH does not change rapidly enough at the end-point (titration curve does not have an almost vertical section)

82
Q

what is a buffer solution

A

one in which the pH of the solution remains approximately constant when small amounts of acid or base are added or the solution is diluted in water

83
Q

an acidic buffer consists of…

A

a solution of a weak acid and one of its salts with a strong alkali

84
Q

a basic buffer consists of…

A

a solution of a weak base and one of its salts with a strong acid

85
Q

adding a base to an acidic buffer

A

in an acidic buffer solution, the weak acid supplies more hydrogen ions when the existing ones are removed by the base.

86
Q

adding acids to an acidic buffer

A

The salt of the weak acid provides the conjugate base to react with the hydrogen ions when small amounts of acid are added.

87
Q

first law of thermodynamics

A

energy is always conserved
Hess’ law: overall reaction enthalpy is the sum of the reaction enthalpies of each step

ΔH=Σ ΔHproducts-ΔHreactants

88
Q

standard enthalpy of combustion

A

enthalpy change when one mole of a substance is completely burned in excess oxygen

89
Q

what are standard conditions

A

one mole of a substance at one atmosphere pressure and any specified temperature (in kelvin)

90
Q

standard enthalpy of formation

A

the enthalpy change when one mole of a compound is formed from its elements in their standard states

91
Q

calorimetry

A

describes the quantitative determination of the change in heat energy which occurs during a chemical reaction

92
Q

spontaneous process

A

mainly exothermic
sometimes endo

most common endo are change of state

93
Q

what are spontaneous endothermic processes always accompanied by

A

an increase in disorder

94
Q

second law of thermodynamics

A

whenever energy is transformed from one fork to another. entropy increases and energy decreases

95
Q

entropy analogy

A

low entropy = tidy room

high entropy = messy room

96
Q

entropy

A

a measure of the disorder in a system

97
Q

entropy change with temperature

A

as temperature increases, entropy increases because particles vibrate more and gaps open up, allowing particles to rotate

98
Q

entropy and complex molecules

A

entropy increases as the moles of vibration increases

99
Q

when does entropy increase?

A
  1. many substances dissolve to form solutions
  2. when a mixture is formed
  3. number of moles increases
100
Q

signs for bond making and breaking

A

breaking +

making -

101
Q

the conversion of energy into work

A

never 100% efficient

work

102
Q

unavailable energy

A

part of the heat change that is never converted into work

103
Q

ΔH=

A

free energy + entropy energy

104
Q

ΔS=

A

ΔS(system) + ΔS(surroundings) = +ve

Σ S(products)-Σ S(reactants)

105
Q

units of entropy change

A

joules per kelvin

106
Q

free energy change

A

combination of enthalpy and entropy change

107
Q

ΔG=

A

ΔH-TΔS

108
Q

negative value for ΔG

A

reaction is likely to happen spontaneously

109
Q

positive value for ΔG

A

reaction unlikely to happen unless external energy is available to do work on the system

110
Q

feasible ΔG=

A

0 or below

111
Q

what does the speed of a reaction depend on?

A

the rate determining step (slowest step)

112
Q

in a reaction aA+bB–>cC

rate=

A

k[A]^m[B]^n

113
Q

rate constant k is only constant if…

A

temperature and activation energy stay constant

114
Q

what are m and n in rate equation

A

the order of reaction for each of the reactants

  • *has to be determined experimentally**
  • no relationship to molar ratios*
115
Q

zero order reactions

A

rate remains constant
[A] does not change the rate

rate=k[A]^0
rate=k

116
Q

first order reactions

A

[A]∝rate
as [A] doubles, rate doubles

Rate=k[A]

117
Q

second order reactions

A

as [A] doubles, rate quadruples

Rate=k[A]^2

118
Q

how to work out overall order of reaction

A

add up the order of reaction for each of the reactants

119
Q

calculating rate constant

A

k=rate/[A][B] (or whatever order of reaction is)

sub in values from any line in table

120
Q

calculating units for rate constant

A

sub in units to rate equation for each term and simplify

121
Q

rate against concentration graphs

A

zero order reaction - horizontal line
first - diagonal line through origin
second- curved line with increasing gradient

122
Q

concentration against time graphs

A

zero - diagonal line from high on conc. axis
first - curved line from high on conc. axis
second - steeper curved line from high on conc. axis

123
Q

what will not be part of the rate determining step

A

a zero order reactant

one not involved in the slow step so will have no effect on rate of reaction

124
Q

one molecule of s reactant involved in the r.d.s is…

A

first order w.r.t. that reactant

125
Q

two molecules of a reactant involved in the r.d.s. is…

A

second order w.r.t. that reactant

Advanced Higher Chemistry (12 decks)

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