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Chemistry > Ch3.2 Physical Chemistry > Flashcards

Ch3.2 Physical Chemistry Flashcards

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1
Q

What can be measured to determine rate of reaction?

A
  • speed of reactant used up or product formed
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2
Q

How can the formation of product or usage of reactants be measured?

A
  • measure mass with a balance
  • measure volume of gas with a gas syringe
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3
Q

What is the formula for calculating rate of reaction?

A

amount of reactant used or product formed ÷ time taken

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4
Q

How can the rate of a reaction be increased?

A
  • increase temperature
  • increase conc of reactant
  • increase pressure of reacting gas
  • increase surface area of solid reactants (to powder)
  • use a catalyst
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5
Q

What is the activation energy of a reaction and how does it relate to collisions?

A
  • activation energy is the minimum energy needed for a reaction to occur
  • this is the amount of energy particles must collide with for the reaction to happen
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6
Q

How does changing concentration and pressure affect collisions?

A
  • increasing pressure means more particles in same volume
  • higher chance of collisions
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7
Q

How does changing the particle size or pressure within a reaction affect collisions?

A
  • more reactant particles in the same volume
  • higher chance of colliding
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8
Q

What is a homogenous catalyst?

A
  • a catalyst in the same phase as the reactant
  • ie. liquid catalyst in a liquid reaction
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9
Q

Give an example of a homogenous catalyst

A

enzymes in bodily fluids

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10
Q

What is a heterogenous catalyst?

A
  • a catalyst in a different state to reactant
  • eg. gas reactants passed over a solid catalyst
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11
Q

How could a catalyst be heterogenous even though all the substances are in the same state?

A

If all are liquids but they are immiscible (don’t mix) then it’s still heterogenous as they are in different layers

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12
Q

What is a dynamic equilibrium?

A

Forward and back reactions occurring at equal and opposite rates, so it looks as though nothing happens when there’s constant change

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13
Q

What are the features of a dynamic equilibrium?

A
  • only in a closed system
  • dynamic at molecular or ionic level
  • visible/macroscopic properties are constant
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14
Q

What is Le Chatelier’s principle?

A

When any of the conditions affecting the position of a dynamic equilibrium are changed, the position of the equilibrium will shift to minimise the change

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15
Q

What happens to the concentration of products/reactants when equilibrium moves left/right?

A
  • equilibrium shifts to right: conc of products increases
  • equilibrium shifts to left: conc of reactants increases
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16
Q

What is the reaction to the action:
increase in conc of reactants

A

Equilibrium shifts to the right

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17
Q

What is the reaction to the action:
decrease in conc of reactants

A

Equilibrium shifts to the left

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18
Q

What is the reaction to the action:
increase in pressure

A

Moves in direction of side with less moles of gas produced to decrease pressure again

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19
Q

What is the reaction to the action:
decrease in pressure

A

Moves towards the side with more moles of gas produced to increase pressure again

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20
Q

What is the reaction to the action:
increase temperature

A

Moves in endothermic direction

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21
Q

What is the reaction to the action:
decrease temperature

A

Moves in exothermic direction

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22
Q

What is the reaction to the action:
catalyst added

A

Reaches equilibrium faster

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23
Q

Describe the stages of the Haber Process

A

1: hydrogen and nitrogen are obtained from natural gas and air respectively. They are pumped into a compressor through a pipe

2: gases are compressed to about 200 atmospheres in the compressor

3: gases are pumped into a tank with layers of catalytic iron beds at 450 degrees C. Some of hydrogen and nitrogen react to form ammonia

4: unreacted gases go into a cooling tank. ammonia is liquefied and removed to pressurised storage vessels

5: unreacted hydrogen and nitrogen are recycled back into the system and started over again

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24
Q

Why does the yield of ammonia change during the Haber Process?

A

Yield of ammonia will change with changes to temperature and pressure

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25
Q

What must companies consider when they want to make a profit from forming ammonia?

A

Availability and cost of raw materials

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26
Q

Is the Haber Process cheap or expensive to start?

A

Cheap
- raw materials are readily available and cheap to purify

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27
Q

What is the process if the cost for a process is too high?

A

No longer economically viable
- many processes require heat and pressure in huge amounts which is expensive

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28
Q

What temperature is the Haber process performed at and why?

A
  • +450 degrees C
  • higher temp favours reverse reaction as it is endothermic
  • higher yield of reactants made
  • lower temp favours forward reaction so higher yield of products made
  • 450 degrees is a compromise condition as a lower temp would be too slow but higher would produce too much of reactants
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29
Q

Is the haber process endo or exo thermic?

A

Endothermic (takes in heat)

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30
Q

Is bond breaking endo or exothermic?

A

Endothermic

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31
Q

Is bond making endo or exothermic?

A

Exothermic

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32
Q

Describe why the pressure condition of the Haber process is what it is

A
  • pressure: 200 atm
  • lower pressure favours production of reactants
  • higher pressure favours production of products
  • high pressure can be dangerous and expensive equipment is needed
  • 200 atm is a compromise of less products being made for expense and safety purposes
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33
Q

What catalyst is used during the Haber process?

A

Iron

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34
Q

Describe how a catalyst affects the Haber process

A
  • iron is the catalyst used
  • doesn’t affect the point of equilibrium, just the rate at which it is achieved
  • speeds up the forward and backward reactions by the same amount
  • gives a higher yield at a lower temperature due to a lower activation energy
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35
Q

What happens during the Haber process without a catalyst?

A
  • higher temp
  • higher costs
  • decreasing yield
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36
Q

What does a higher temp cause in a reaction?

A

More molecules will have the activation energy

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37
Q

What does a catalyst cause in a reaction?

A

Lowers activation energy so more molecules are likely to have it

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38
Q

What are CFCs?

A
  • chlorofluorocarbons
  • made by Thomas Midgely
  • destroy ozone layer
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39
Q

What is the difference between nitrogen dioxide and dinitrogen tetraoxide?

A

Nitrogen dioxide is brown
Dinitrogen tetraoxide is colourless

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40
Q

What yield of ammonia do the compromise conditions of the Haber process produce?

A

18.3% yield at 200 atm and 450 degrees C

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41
Q

What are the uses of ammonia?

A
  • 80% used for making fertilisers such as ammonium sulphate
  • smaller % used for making nitric acid (used to make explosives) and polymers such as nylon
42
Q

What symbol is used for the equilibrium constant?

A

Kc

43
Q

Where is the equilibrium if the Kc is between 0 and 1?

A

It lies to the left

44
Q

Where is the equilibrium if the Kc is over 1?

A

It lies to the right

45
Q

What does the term enthalpy mean?

A

Used to distinguish between the heat energy taken in or out of a reaction compared to other types of energy

46
Q

What symbol is used to represent the term enthalpy?

A

∆H

47
Q

Compare endo and exothermic reactions

A
  • chemical reactions in which the system loses heat energy to its surroundings are exothermic
  • chemical reactions that absorb energy from its surroundings are endothermic
48
Q

What are enthalpy changes measured in?

A

kilojoules per mole

49
Q

What is bond enthalpy?

A

The amount of energy covalent bonds have locked up in them. This is the amount of energy it will take to break one mole of these bonds.

50
Q

What are standard conditions?

A
  • the agreed criteria that scientists use to measure enthalpy cycles
  • 25 degrees C
  • 298 K
  • 100 kPa
51
Q

What does ΔH⁰c mean?

A

one mole of a substance has completely combusted

52
Q

What does ΔH⁰f mean?

A

one mole of a substance has formed from its constituent elements in their standard states

53
Q

What does ΔH⁰neut mean?

A

one mole of water forms when an acid reacts with a base

54
Q

What does ΔH⁰sol mean?

A

one mole of a substance is dissolving

55
Q

What does ΔH⁰r mean?

A

one mole of a substance is reacting
(the reaction isn’t combustion formation, solution or neutralisation)

56
Q

Describe the process of cup calorimetry

A
  • we mix solutions in a polystyrene cup and measure the amount of energy transferred to or absorbed from the water
57
Q

What do you need to carry out a calorimetric calculation?

A
  • vol of solution
  • mass of any solid reactant added
  • initial and final temps of solution
58
Q

Describe the stages of a calorimetric calculation

A
  • work out energy transfer in joules using q = mcΔt
  • change J into kJ
  • work out number of moles of chemical involved
  • divide kilojoules by moles
59
Q

When would can calorimetry be used compared to cup?

A
  • when the temperature change would melt the polystyrene cup
60
Q

What is bomb calorimetry?

A
  • a technique that overcomes the limitations of cup and can calorimetry
61
Q

What does en enthalpy cycle allow?

A
  • provides an indirect method of measuring the enthalpy change of a chemical reaction
62
Q

What is another term for an enthalpy cycle?

A

A Hess cycle

63
Q

What does Hess’ law state?

A
  • the enthalpy change in a chemical reaction is independent of the route it takes
  • (if the start and end points are the same the overall enthalpy change will be the same)
64
Q

What does it imply if the examiners provide us with ΔH⁰c values?

A
  • that we are separately completely combusting the reactants and products in the original reaction
65
Q

What is the equation used for calculating enthalpy change?

A

q = mcΔt
q is energy change in J
m is mass
c is specific heat capacity (4.18)
Δt is temp change

66
Q

Define bond enthalpy

A

The energy required to break 1 mole of gaseous bonds into gaseous atoms

67
Q

What is enthalpy change of formation?

A
  • the enthalpy change when 1 mole of a substance is formed from its constituent elements
68
Q

What is enthalpy change of combustion?

A
  • the enthalpy change when 1 mole of substance is completely burned in excess oxygen
69
Q

Describe the first law of energy

A
  • energy can neither be created nor destroyed but it can be converted from one form to another
  • all chemical reactions are accompanied by some form of energy change
  • changes can be very obvious but in many cases go unnoticed
70
Q

Give 2 examples of exothermic reactions

A
  • combustion of fuels
  • respiration
71
Q

Give 2 examples of endothermic reactions

A
  • photosynthesis
  • thermal decomposition
72
Q

What is enthalpy change of formation?

A
  • the enthalpy change when one mole of water is formed from its ions in dilute solution
73
Q

During calorimetry, how does the temp change of the water determine the nature of the reaction?

A
  • water heats up = exothermic
  • water cools down = endothermic
74
Q

Define enthalpy change of formation

A

The enthalpy change of formation is the enthalpy change when 1 mole of a substance is formed from its elements in their normal state under standard conditions

75
Q

Define enthalpy change of combustion

A

The enthalpy change of combustion is the enthalpy change when 1 mole of a substance is completely burned in an excess of oxygen under standard conditions

76
Q

Define enthalpy change of neutralisation

A

The enthalpy change of neutralisation is the enthalpy change when 1 mole of water is formed in a reaction between an acid and a base under standard conditions

77
Q

What do spectroscopic techniques use?

A
  • they use various parts of the electromagnetic spectrum to analyse the structure of matter
78
Q

Describe IR spectroscopy

A
  • infrared radiation makes chemical bonds in covalently bonded substances vibrate
  • each type of bond vibrates in response to a different frequency of infrared radiation
  • we can use these absorptions to identify the bonds
79
Q

Compare a sample cell and a control cell within IR spectroscopy

A

sample cell:
NaCl disc, smear sample ground up in Nujol onto disc, place second NaCl disc on top

control cell:
same as above without sample

80
Q

Why are NaCl discs used during IR spectroscopy?

A
  • NaCl contains purely ionic bonds so won’t flare up spectrometer
81
Q

Why isn’t water used for grinding up the sample used in IR spectroscopy?

A

It will dissolve the NaCl discs

82
Q

What is the vibration value of O-H in alcohols and phenols?

A

3200-3600

83
Q

What is the vibration value of O-H in carboxylic acids?

A

2500-3300

84
Q

What is the vibration value of C=O in aldehydes, ketones and carboxylic acids?

A

1630-1820

85
Q

Name 2 oxidising agents

A
  • potassium dichromate K2Cr2O7
  • potassium manganate KMnO4
86
Q

Name a reducing agent

A
  • sodium borohydride NaBH4
87
Q

How can a primary alcohol be oxidised?

A
  • oxidised with distillation to aldehyde
  • oxidised with reflux to aldehyde then carboxylic acid
88
Q

How can a secondary alcohol be oxidised?

A
  • oxidised to a ketone only
89
Q

How can a tertiary alcohol be oxidised?

A

It cannot be oxidised

90
Q

What can happen in the high energy environment of the ionisation chamber in mass fragmentation spectra?

A
  • 2 things:
  • the parent molecules may have an electron knocked off, turning into molecular ions
  • the parent molecules will get broken up into a series of smaller pieces which we call fragments
91
Q

How can the mass fragmentation spectra be used?

A
  • used to work out the structure of the original molecule
  • computer scales the peak of the most abundant fragment to 100 (base peak)
92
Q

What is the molecular ion peak in a mass fragmentation spectra?

A
  • the peak at which the original molecule’s Mr would be
  • there may be peaks higher than this but this is due to carbon and hydrogen both having heavier isotopes
93
Q

Describe the blue litmus wet test

A
  • tests for carboxylic acid/phenol
  • carboxylic acid turns it red
  • phenol turns it pink
94
Q

Describe the acidified potassium dichromate wet test

A
  • tests for aldehyde/primary alcohol/secondary alcohol
  • orange to green if positive
95
Q

Describe the 2,4-dinitrophenylhydrazine wet test

A
  • test for aldehyde/ketone
  • positive = orange precipitate
96
Q

Describe the sodium carbonate wet test

A
  • tests for carboxylic acids
  • fizzes and produces gases that turn limewater milky
97
Q

Describe the neutral iron (III) chloride wet test

A
  • test for phenol
  • brown to purple
98
Q

Describe the Tollens wet test

A
  • test for aldehyde
  • makes silver mirror
99
Q

Describe the sodium metal wet test

A
  • test for alcohol/carboxylic acid
  • fizzing (more vigorous with carboxylic acid)
100
Q

Describe the bromine water wet test

A
  • test for C=C bond
  • orange to colourless
101
Q

Describe the warmed with ethanoic acid and sulphuric acid wet test

A
  • test for alcohol
  • positive result: fruity smell produced (ester formed)
102
Q

What is the formula for percentage error?

A

% error =
error margin/actual measurement
x 100

Chemistry (17 decks)

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