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Chemistry > Fuels and heats of reactions > Flashcards

Fuels and heats of reactions Flashcards

1
Q

Hydrocarbon

A

a compound that contains carbon and hydrogen only

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2
Q

Organic chemistry

A

the study of the compounds of carbon

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3
Q

Common sources of hydrocarbons

A
  1. Coal
  2. Natural gas (Methane)
  3. Petroleum (Crude oil)
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4
Q

Fossil fuels

A

fuels that were formed from the remains of animals that lived millions of years ago

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5
Q

Alkanes

A
  1. from a family of hydrocarbons where all the atoms are linked by single bonds
  2. Methane is the simplest alkane, formed by decomposition of animal waste and vegetation
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6
Q

First ten members of the alkane group

A
  1. Methane - CH4
  2. Ethane - C2H6
  3. Propane - C3H8
  4. Butane - C4H10
  5. Pentane - C5H12
  6. Hexane - C6H14
  7. Heptane - C7H16
  8. Octane - C8H18
  9. Nonane - C9H20
  10. Decane - C10H22
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7
Q

States of alkanes

A

First 4 - gases
next 12 - liquids
higher members - waxy

boiling point increases with size of molecules - increasing van der Waals

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8
Q

Homologous series

A
  1. A series of compounds of similar chemical properties
  2. Showing gradations in physical properties
  3. Having a general formula for its members
  4. Each member having a similar method of preparation
  5. Each member differing from the previous member by a (CH2) unit.
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9
Q

Structural isomers

A

Same molecular formula but different structural formula

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10
Q

Naming Alkanes

A
  1. Find the longest continuous chain of carbons
  2. Number the carbon chain - with the branches getting the lowest number if possible
  3. Indicate the type and position of each branch
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11
Q

Alkenes

A

unsaturated compound

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12
Q

Unsaturated compound

A

one which contains one or more double/triple bonds between the atoms in the molecule

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13
Q

Naming alkenes

A
  1. Find the longest chain of continuous carbon atoms containing the C = C double bond.
  2. Number the chain starting at the end nearest to the C = C double bond
  3. Indicate the type and position of each substituent
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14
Q

Examples of alkenes

A
  1. Ethene - C2H4
  2. Propene -C3H6
  3. Butene - C4H8
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15
Q

Experiment:
To prepare ethene and examine its properties (equipment)

A

Need:
1. Retort stand
2. Test tube x2
3. Bunsen burner
4. Water trough

  1. Aluminium oxide
  2. Glass wool
  3. Ethanol
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16
Q

Experiment:
To prepare ethene and examine its properties (Explained)

A
  1. The aluminium oxide acts as both a dehydrating agent and a catalyst
  2. The glass wool is placed in the boiling tube in order to soak up the ethanol and hold it in place at the end of the horizontal boiling tube.
  3. The first test-tube is usually discarded since it contains a mixture of ethene and air.
  4. Before turning off the Bunsen burner, the delivery tube is removed from the water to prevent “suck back” of water.
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17
Q

Experiment:
To prepare ethene and examine its properties (Physical properties)

A
  1. Ethene is a colourless gas with a sweetish smell.
  2. It is insoluble in water but soluble in organic solvents.
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18
Q

Experiment:
To prepare ethene and examine its properties (Chemical properties)

A

(a) Combustion: The gas burns with a yellow luminous flame.If limewater is added to the gas jar in which the ethene has been burned, the limewater turns milky.

(b) Addition of bromine water: The change of colour from red to colourless is a test for unsaturation.

(c) Addition os KMnO4: The change of colour from purple to colourless is a test for unsaturation.

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19
Q

Alkynes

A
  1. Ethyne is the only alkyne on the course. C2H2.
  2. Ethyne is used in oxyacetylene welding and cutting.
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20
Q

Experiment:
To prepare ethyne and examine its properties. (Points)

A
  1. Calcium carbide cannot be obtained in a pure state.
  2. The fizzing is caused by the ethyne gas given off in the reaction.
  3. The reaction, CaC2 + 2H2O -> Ca(OH)2 + C2H2
  4. The white substance formed in the flask is calcium hydroxide
  5. The flask gets warm because the reaction gives out heat (exothermic)
  6. The impure ethyne is bubbled through acidified copper sulfate solution to remove gases such as hydrogen sulphide, phosphine, and ammonia, which come from the impurities in the calcium carbide.
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21
Q

Experiment:
To prepare ethyne and examine its properties. (Physical properties)

A
  1. Ethyne is a colourless gas with a sweetish smell. It is insoluble in water but soluble in organic solvents.
22
Q

Experiment:
To prepare ethyne and examine its properties. (Chemical properties)

A

(a) Combustion: It burns with a luminous smoky flame.

(b) Addition of bromine water: The red colour of the bromine water changes to colourless. This is evidence for the fact that ethyne is unsaturated.

(c) Addition of acidified KMnO4: The purple colour disappears. This is evidence for the fact that ethyne is unsaturated.

23
Q

Aromatic hydrocarbons

A
  1. Aliphatic compounds are compounds that do not contain double or triple carbon bonds.
  2. Aromatic compounds are compounds that contain a benzene ring
24
Q

Oil refining

A
  1. Fractional distillation separates crude oil into different useful components - separated by boiling points.
  2. The temperature decreases as you go up the column - heavier fractions and large molecules liquify on the bottom columns, the vapour from lighter fractions and smaller molecules rises up through each section until the temperature reaches its boiling point and condenses on that particular shelf.
25
Q

Refinery gas

A

methane, ethane, propane, butane

26
Q

Since gases are odourless

A

Sulfur compounds - mercaptans are added to give an unpleasant smell do that gas leaks can be detected

27
Q

Natural gas

A

almost pure methane

28
Q

Bottled gas

A

a mixture of propane and butane, liquified under pressure - LPG (Liquified petroleum gas).

29
Q

Petrol

A

aka light gasoline, a mixture of at least 100 different compounds, mainly hydrocarbons - C5 - C10

30
Q

Octane number

A

of a fuel is a measure of the tendency of the fuel to resist knocking

31
Q

Assigning octane numbers

A
  1. High octane numbers - a very efficient fuel as it does not auto-ignite readily (iso-octane, 2,2,4).
  2. Low octane numbers - a very inefficient fuel as it readily auto ignites (Heptane).
  3. The shorter the alkane chain, the higher the octane number
  4. The more branched the chain, the higher the octane number.
  5. Cyclic compounds have a higher octane number than straight-chain compounds.
32
Q

Making petrol

A
  1. Adding small amounts of tetraethyl lead helps reduce knocking.
  2. The use of lead additives in petrol is banned in Ireland due to health risks - lead pollution.
  3. Alternatives to lead,
    -Isomerisation
    -Catalytic cracking,
    -Dehydrocyclisation
    -Adding oxygenates.
33
Q

Isomerisation

A
  1. Changing straight-chain alkanes into their isomers.
  2. Done by heating the alkanes in the presence of a suitable catalyst
  3. An equilibrium mixture of straight-chain and branched isomers are usually produced.
34
Q

Catalytic cracking

A
  1. the breaking down of long-chain hydrocarbon molecules by the action of heat and catalysts into short-chain molecules for which there is greater demand.
  2. Done by heating the heavier fractions in the presence of a catalyst
35
Q

Dehydrocyclisation

A
  1. involves the use of catalysts to form ring compounds
  2. Straight-chain alkanes are converted to cycloalkanes
  3. Cycloalkanes are converted to aromatic compounds. Aromatic compounds have high octane numbers.
  4. Dehydrocyclisation comes from the fact that hydrogen is being removed and ring compounds are formed.
36
Q

Adding oxygenates

A
  1. oxygenate - a fuel that contains oxygen in its molecules
  2. oxygenates commonly added to petrol to increase its octane number - methanol, ethanol, MTBE
  3. give rise to little pollution wen burned.
37
Q

Methods of manufacturing hydrogen

A

(a) Steam performing of natural gas:
involves reacting methane with steam in the presence of a suitable catalyst.

(b) electrolysis of water:
an expensive way of producing hydrogen - high cost of electricity.
hydrogen is used in the manufacture of ammonia and for hydrogenating vegetable oils in the manufacture of margarine.

38
Q

Exothermic reaction

A

one that produces heat
negative value for ΔH

39
Q

Endothermic reaction

A

one that takes in heat
positive value for ΔH

40
Q

Heat of reaction

A

is the heat change when the numbers of moles of reactants indicated in the balanced equation for the reaction react completely

41
Q

Combustion reaction

A

A reaction in which a substance is burned

42
Q

Heats of combustion

A
  1. of a substance is the heat change when one mole of the substance is completely burned in excess oxygen
  2. accurately measured using a bomb calorimeter - used to give an indication of the efficiency of fuels
43
Q

Kilogram calorific value

A
  1. of a fuel is the heat energy produced when 1kg of the fuel is completely burned in oxygen.
  2. used to compare the efficiencies of various fuels
44
Q

Bond energy

A
  1. is the average energy required to break one mole of a particular covalent bond and to separate the neutral atoms completely from each other.
45
Q

Heat of neutralisation

A
  1. is the heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base.
  2. measured in KJmol-1
  3. The same for all strong acid-strong base because both strong acids and gases are fully dissociated in dilute aqueous solutions.
  4. When either a weak acid or weak base is involved, the ΔH number is less tan -57 KJmol-1. because weak acids are not fully dissociated in water.
46
Q

For complete neutralisation to occur and form one mole of water

A

the weak acid or base must become fully dissociated. This dissociation requires energy (endothermic). Therefore, the eat released will be less than 57KJ.

47
Q

experiment:
To determine the heat of reaction of hydrochloric acid with sodium hydroxide (What’s needed).

A

-Thermometer
-Polystyrene cup
-50cm3 of 1M HCL
-50cm3 of 1M NaOH
-Lid
-Stirrer
-HCL + NaOH mixture

48
Q

experiment:
To determine the heat of reaction of hydrochloric acid with sodium hydroxide (points)

A
  1. Using a graduated cylinder, a known volume of HCL solution is placed in a polystyrene cup.
  2. The same volume of sodium hydroxide of the same concentration is placed in a second polystyrene cup.
  3. The volumes and concentrations of HCL and NaOH used are recorded.
  4. Both solutions are allowed to stand until they are at the same temperature
  5. The temperature of each solution is recorded
  6. The sodium hydroxide solution is quickly added to the HCL solution and care is taken to avoid any loss of liquid due to splashing.
  7. A lid is placed immediately on the polystyrene cup in which the two solutions have been mixed.
  8. The solution is stirred continuously
  9. The maximum temperature reached by the mixture is recorded
49
Q

experiment:
To determine the heat of reaction of hydrochloric acid with sodium hydroxide (accuracy)

A
  1. Use an accurate thermometer
  2. The quick addition of the base to the acid alps to avoid heat loss.
  3. A burette could not be used to mix the solutions as the mixing would be too slow and eat would be lost to the surroundings.
50
Q

Heat of formation

A

The heat change that takes place when one mole of a compound in its standard state is formed from its elements in their standard states.

51
Q

Hess’s law

A

States that, if a chemical reaction takes place in a number of stages, the sum of heat changes in the separate stages is equal to the eat change if the reaction is carried out in one stage.

52
Q

The law of conservation of energy

A

states that energy cannot be created nor destroyed but one converted from one form of energy into another

Chemistry (32 decks)

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