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Chemistry > Unit 2 Questions > Flashcards

Unit 2 Questions Flashcards

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1
Q

What is the definition of enthalpy?

A

The heat content of a system at constant pressure.

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2
Q

In an exothermic reaction, is the H of the products or reactants bigger and why?

A

The H of the reactants is bigger because it has a negative deltaH.

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3
Q

What is the standard temperature in degrees celcius?

A

25 degrees

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4
Q

Give the definition of the standard enthalpy change of formation.

A

The enthalpy change when one mole of a substance is formed from its constituent elements in their standard states under standard conditions.

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5
Q

Give the definition of the standard enthalpy change of combustion.

A

The enthalpy change when one mole of a substance is completely combusted in oxygen under standard conditions.

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6
Q

State Hess’s law

A

The total enthalpy change for a reaction is independent of the route taken from reactants to products.

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7
Q

You got this!

A

You’re doing so well!! :)

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8
Q

What is the definition of bond enthalpy?

A

The enthalpy needed to break a covalent X-Y bond into X atoms and Y atoms all in the gas phase.

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9
Q

What is the average bond enthalpy?

A

The average enthalpy needed to break a certain type of covalent bond of a gaseous species.

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10
Q

Why is there a difference between bond enthalpy and average bond enthalpy?

A

Because the bond enthalpy varies depending on the structure of the rest of the molecule.

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11
Q

Is breaking bonds exothermic or endothermic?

A

Endothermic because it needs energy.

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12
Q

Which equation gives you Q?

A

Q=mc/\t where /\ is my rubbish delta :)

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13
Q

Which equation gives you /\H?

A

/\H = -Q/n

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14
Q

State the full equation for working out /\H.

A

/\H = -(mc/\t)/n

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15
Q

Which two practicals can be used to indirectly determine /\H?

A

Calorimeter and combustion of fuel.

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16
Q

Define the rate of reaction

A

The change in concentration of a product or reactant per unit time.

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17
Q

Explain briefly the relationship between rate and concentration of reactants.

A

Reactant concentration high at start => rate high at start.
Reactant concentration decreases => rate decreases.
Reactant concentration reaches zero => rate drops to zero.

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18
Q

How do you calculate the rate at any point from a graph?

A

Draw a tangent and work out the gradient.

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19
Q

Which experiment would you use to find the relationship between initial rate and initial concentration?

A

A series of experiments where one reactant is changed at a time.

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20
Q

Give the four factors affecting rate

A
  1. Concentration of solution (pressure of gas)
  2. Surface area of solid
  3. Temperature of reaction
  4. Light (only in reactions like photosynthesis)
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21
Q

Define activation energy

A

The minimum energy needed to break a covalent bond and start a reaction.

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22
Q

What are the two conditions for a successful collision?

A
  1. Must have sufficient energy

2. Must collide in the correct orientation

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23
Q

Give the definition of a catalyst

A

A substance that increases the rate of reaction by providing an alternative route with lower activation energy without being used up in the process.

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24
Q

Give the definition and an example of a homogenous catalyst

A

A homogenous catalyst is in the same phase as the reactants. E.g., concentrated sulfuric acid in formation of ester.

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25
Q

Give the definition and an example of heterogeneous catalysts.

A

Heterogeneous catalysts are in a different phase to the reactants. E.g., iron in the Haber process.

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26
Q

Give three benefits of heterogeneous catalysts

A
  1. Easily separated from products
  2. Saves energy costs
  3. Benefits environment (less fossil fuel/ CO2)
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27
Q

Give four benefits of the use of enzymes as catalysts

A
  1. Lower temp and pressure needed
  2. Mild conditions - no harm to food and fabrics
  3. Biodegradable - no disposal problems
  4. Pure products without side reactions - no need to separate.
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28
Q

State four properties that vary with time and can therefore be used to measure rate

A
  1. Change in gas volume (gas syringe)
  2. Change in mass (weighing balance)
  3. Change in colour (colorimeter)
  4. Change in gas pressure (manometer)
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29
Q

Which four substances are added to the beaker so start with when studying the iodine clock reaction?

A

Sodium thiosulfate, starch solution, potassium iodide, sulfuric acid.

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30
Q

What is added to the beaker as a second step in the iodine clock reaction?

A

Hydrogen peroxide

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31
Q

In the iodine clock reaction, which substance’s concentration is altered across experiments?

A

The hydrogen peroxide

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32
Q

Which substance makes the starch turn blue?

A

Iodine (not iodide!)

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33
Q

Which substance prevents the mixture turning blue immediately and why?

A

The sodium thiosulfate, because it turns the iodine back into iodide.

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34
Q

Give the equation of the iodide ions turning into iodine

A

H2O2 + 2H+ + 2I- —-> 2H2O _ I2

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35
Q

Give the equation involving thiosulfate

A

I2 + 2S2O3^2- —-> 2I- + S4O6 ^ 2-

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36
Q

Define hydrocarbons and functional groups

A

A hydrocarbon is a substance containing only hydrogen and carbon. A functional group is the group of atoms that gives the compound its characteristic properties.

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37
Q

Describe briefly these forms of writing fomulas:

  1. Molecular
  2. Displayed
  3. Shortened
  4. Skeletal
A
  1. Molecular C6H11Br. Literally just the elements and no structural information
  2. Displayed The big spidery-looking one with all the annoying hydrogens
  3. Shortened Like molecular but shows structure.
  4. Skeletal Even more spidery.
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38
Q

Define structural isomers

A

Compounds with the same formula but different structures

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39
Q

Define chain isomerism

A

Isomers where the C-chain changes. (what we did at GCSE. happier times.)

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40
Q

Surprise for you!

A

( o˘◡˘o) ┌iii┐

Cake for you because you deserve it and you’re doing so well! Keep going :)

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41
Q

Explain where E-Z isomerism can be found

A

In alkenes with restricted rotation about the double bond

42
Q

Which forces do melting and boiling points depend mainly on?

A

Van der Walls forces

43
Q

Which forms of bonding can be found in hydrocarbons?

A

Only induced dipole-induced dipole forces. Weak!

44
Q

What effect does hydrocarbon chain length have on melting and boiling point? Why? What can you say about chain isomerism in relation to this issue?

A

The longer the chain, the higher the melting and boiling points. This is because VdW forces only occur on the surface, so small hydrocarbons have a smaller surface area and therefore a smaller melting point.
The more branches an isomer has, the lower the boiling point and the more volatile it is :)

45
Q

What do you need an excess of for complete combustion?

A

Why, O2 of course!

46
Q

Name 2 advantages and 4 disadvantages of fossil fuels.

A

Advantages:

  1. Large variety - can use most appropriate fuel
  2. Available at all times - reliable to an extent

Disadvantages:

  1. Non-renewable
  2. Combustion releases CO2 - fossil fuel, global warming
  3. Incomplete combustion releases toxic carbon monoxide, CO
  4. Produces sulfur dioxide which causes acid rain
47
Q

What does halogenation mean

A

Halogenation is a reaction with any halogen

48
Q

What is a radical

A

A species with an unpaired electron

49
Q

Explain the difference between homolytic and heterolytic bond fission

A

Heterolytic bond fission sees the electrons both move to the same side and forming ions.
Homolytic bond fission has the electrons move to opposite sides, forming free radicals.

50
Q

How reactive are alkanes and why.

A

Alkanes are unreactive because they are non-polar and do not contain double bonds.

51
Q

What do alkanes produce when combusted in oxygen?

A

H2O and CO2

52
Q

Why is CO toxic?

A

Because it inhibits the transport of oxygen around the body

53
Q

What needs UV light to react with alkanes?

A

Halogens. Halogens react with alkanes in UV light.

54
Q

Describe briefly what happens during initiation.

A

UV light breaks the Cl=Cl bond homolytically to give 2Cl*

55
Q

Give the chain propagation reaction starting with Cl*

A

Cl* + CH4 –> CH3* + HCl

56
Q

Give the chain propagation reaction starting with the free radical CH3*

A

CH3* + Cl2 —> CH3Cl + Cl*

57
Q

How is a pi bond formed

A

By the sideways overlap of p electrons

58
Q

What type of bonding is to be found in the double bond of alkenes?

A

A 3.14159265358979323846264338327950288419716939937510 bond of course! tee hee

59
Q

What type of attack are alkenes susceptible to and why?

A

They are susceptible to an attack by an electrophile because of the high electron density of the pi bond

60
Q

State the two mechanisms by which a H-Br molecule can react with a hydrocarbon

A
  1. Heterolytic bond fission

2. Electrophilic addition

61
Q

Explain how a non-polar species can attack the pi bond of an alkene

A

Through a dipole induced by the pi bond

62
Q

Describe two tests for the presence of a double bond

A

Bromine (aqueous is safer) turns from brown to colourless in the presence of an alkene
Potassium manganate turns from purple to colourless in the presence of an alkene

63
Q

What is hydrogenation of alkenes catalysed by?

A

Nickel

64
Q

What is hydrogenation of alkenes used for?

A

To convert oils into more saturated edible fats

65
Q

What is hydrogenation

A

Addition of hydrogen to an alkene

66
Q

What type of polymerisation do alkenes undergo?

A

Addition polymerisation where the double bond is used and nothing is eliminated.

67
Q

What can catalysts be used for in polymerisation?

A

To make straight chains which have higher density and melting temperature

68
Q

What is hydrolysis

A

A reaction with water to produce a new product

69
Q

What is a nucleophile?

A

A species with a lone pair of electrons which it would very much like to donate

70
Q

Which type of attack is the carbon in a halogenoalkane susceptible to and why?

A

It is susceptible to nucleophilic attack because the halogen is more reactive than the carbon, creating a polar molecule where the carbon is delta positive and the halogen delta negative.

71
Q

How can we speed up hydrolysis (OH replaces halogen)? (two ways)

A

Heated under reflux or addition of aqueous sodium hydroxide NaOH

72
Q

What is a more powerful factor in reaction speed: bond strength or electronegativity?

A

Bond strength of course.

73
Q

Which two functional groups are needed for a hydrocarbon to be soluble in water and why?

A

O-H or N-H because only they can form a hydrogen bond with water.

74
Q

Name three uses of halogenoalkenes

A
  1. As solvents
  2. As anesthetics
  3. As refrigerants
75
Q

Describe briefly why halogenoalkanes are good solvents

A

They are insoluble in water (no OH or NH so no H bonding) but can mix with many other organic substances

76
Q

Describe briefly why halogenoalkanes are good refrigerants

A

Because small halogenoalkanes have boiling points very close to room temperature meaning liquids can be easily evaporated and solids easily liquified. When a liquid vapourises it takes energy from the surroundings thereby cooling them.

77
Q

State a halogenoalkane that can be used as an anesthetic

A

Trichloromethane (chloroform)

You’re doing so well! Keep going and make yourself some pancakes later!

78
Q

What does fermentation do?

A

Converts sugar to ethanol

79
Q

How is ethanol produced?

A

By reacting ethene with steam

80
Q

Which substance catalyses the production of ethanol?

A

Phosphoric acid

81
Q

What are the conditions for the production of ethanol?

A

300 degrees for high yield and rate and 60-70 atm.

82
Q

How can alcohol by separated after fermentation?

A

Fractional distillation

83
Q

Guess what

A

It’s not in your hands

84
Q

Define a biofuel

A

A biofuel is a fuel that has been produced using a biological source

85
Q

Give three advantages of biofuels

A
  1. Renewable (using freshly grown plants, etc)
  2. Carbon neutral (release only as much as they have taken out
  3. Better economic and political stability (no need to import/rely on other countries for fossil fuels if you don’t have any)
86
Q

Give three disadvantages of biofuels

A
  1. Woodland often cut down to produce land - land also cannot produce food crops
  2. Large quantities of water and fertilizer needed - causes water shortages and pollution
  3. Energy needed to transport the resulting fuel and build factories so not really carbon neutral after all
87
Q

What does an alcohol form when dehydrated?

A

An alkene

88
Q

Draw the dehydration of propanol

A

. . l . . l . . l . . . . . . . . . . . . . l . . l . . .l
- C - C - C - O - H —–> - C - C = C + H - O - H
. . l. . . l. . .l. . . . . . . . . . . . . l. . .l. . . .l

I tried my best with the diagram. Ignore the dots.

89
Q

How many other carbons is the C-OH carbon joined to in a primary alcohol?

A

Less than or equal to one

90
Q

How many other carbons is the C-OH carbon joined to in a secondary alcohol?

A

Two

91
Q

How many other carbons is the C-OH carbon joined to in a tertiary alcohol

A

Three

92
Q

Name the product(s) of a primary alcohol’s oxidation(s)

A
  1. (propan)al - aldehyde

2. (propan)oic acid - carboxylic acid

93
Q

Name the product(s) of a secondary alcohol’s oxidation(s)

A

(propan)one - ketone

94
Q

Name the product(s) of a tertiary alcohol’s oxidation(s)

A

(2-methylpropan-2-)ol - just an alcohol because tertiary alcohols don’t get oxidised!

95
Q

What is the reaction that takes place when testing for a primary or secondary alcohol, which reagents are used, and what is the observation?

A

Oxidation, acidified potassium dichromate, orange to green

96
Q

Give the definition of a weak acid

A

One that only partially ionises in an aqueous solution

97
Q

Are carboxylic acids strong or weak?

A

Weak!

Unlike you, my dear :)

98
Q

Acid + Base –>

A

Salt + water

99
Q

Acid + carbonate —>

A

Salt + carbon dioxide + water

100
Q

Acid + alcohol —>

A

Ester + water (that one’s nasty)

101
Q

Describe the smell of esters

A

Sweet and fruity :)

102
Q

Guess what.

A

You are doing so well. God is with you.

Chemistry (9 decks)

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