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Chemistry > Fuels & Heats Of Reaction (chpt 21) > Flashcards

Fuels & Heats Of Reaction (chpt 21) Flashcards

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1
Q

Organic chemistry

A

The study of compounds of carbon

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2
Q

Hydrocarbon

A

A compound that contains carbon and hydrogen only

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3
Q

Fossil fuels

A

Fuels that were formed from the remains of plants and animals that lived millions of years ago

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4
Q

Saturated compound

A

One in which there are only single bonds between the atoms in the molecule

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5
Q

Alkanes

A

Saturated compounds
Differ by a CH2 unit

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6
Q

Homologous series

A

A series of compounds of similar chemical properties, showing graduation in physical properties, having a general formula for its members, each member having a similar method of preparation, each member differing from the previous member by a CH2 unit

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7
Q

Structural isomers

A

Compounds with the same molecular formula

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8
Q

Unsaturated compound

A

One that contains one or more double or triple bonds between carbons in the molecule

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9
Q

Alkenes

A

Homologous series
Double carbon bond

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10
Q

Alkynes

A

Carbon triple bond
Highly unsaturated
E.g. ethyne, used for welding

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11
Q

Fractional distillation

A

The separation of crude oil into a number of useful parts

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12
Q

Steps in fractional distillation

A

1. Hot crude oil mixture enters the fractionating column
2. Trays collect the condensed liquid and the bubble caps slow down the rate at which the vapour rises to increase the contact time between the vapour and the liquids in the column
3. Molecules with high boiling points turn to liquids near the bottom of the column

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13
Q

Octane number

A

The measure of the tendency of a fuel to resist knocking

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14
Q

Knocking

A

The premature ignition of the petrol - air mixture in the engine before normal ignition of the mixture by a spark

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15
Q

Auto ignition

A

The premature ignition of the petrol - air mixture in the engine before normal ignition of the mixture by a spark

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16
Q

Pinking

A

The premature ignition of the petrol - air mixture in the engine before normal ignition of the mixture by a spark

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17
Q

Factors affecting the octane number

A

Length of carbon chain - shorter chain , higher octane
Degree of branching - more branches , higher octane
Cyclic compounds have a higher octane than straight-chain compounds

18
Q

Name a compound with an octane number of 0

A

Heptane C7H16

19
Q

Name a compound with an octane number of 100

A

2,2,4 trimethyl pentane C8H18

20
Q

Isomerisation

A

Changing straight-chain alkanes into their isomers
→ increases octane number of a fuel
→ carried out by heating alkanes in the presence of a catalyst causing the chains to break and rejoin

21
Q

Catalytic cracking

A

The breaking down of long-chain hydrocarbon molecules by the action of heat and catalysts into short-chain molecules for which there is higher demand
The alkenes produced are important feedstock for the petrochemical industry

E.g. Alkane → branched alkane + alkene

22
Q

Dehydrocyclisation

A

The use of catalysts to form ring compounds
→ hydrogen is removed and ring compounds are formed

Straight - chain alkanes → cycloalkanes
Cycloalkanes → aromatic compounds (higher octane no.)

23
Q

Methods of making petrol

A

1. Isomerisation
2. Catalytic cracking
3. Dehydrocyclisation
4. Adding oxygenates

24
Q

What structural feature does 2,2,4 trimethyl pentane have to account for its octane number of 100

A

Short branched chain

25
Q

Suggest why elemental hydrogen does not occur in nature on earth as a fuel source

A

Too reactive

26
Q

Give a major source of hydrogen gas

A

- steam reforming
- electrolysis of water
- dehydrocyclisation

27
Q

Steam reforming

A

Reacting methane with steam in the presence of a suitable catalyst

28
Q

Electrolysis of water

A

Method of manufacturing hydrogen gas

Expensive due to cost of electricity

29
Q

Uses of hydrogen gas

A

- Manufacture of ammonia
- fuel → abundant and good for environment as the only byproduct is water

30
Q

Exothermic reaction

A

Heat is given out

Delta H = positive

31
Q

Endothermic reaction

A

Heat is taken in

Delta H = negative

32
Q

Heat of reaction

A

The heat change when the number of moles of reactants indicated in the balanced equation for the reaction react completely

Delta H (triangle H)

33
Q

Heat of combustion

A

The heat change given off when one mole of the substance is completely burned in excess oxygen

34
Q

How is heat of combustion measured

A

Using a bomb calorimeter

35
Q

Kilogram calorific value

A

The heat energy produced when 1kg of fuel is completely burned in oxygen

36
Q

Bond energy

A

The average energy required to break one mole of a covalent bond and to separate the neutral atoms completely from each other

37
Q

Heat of neutralisation

A

The heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base

38
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

Standard state is its normal form at 25°c and 101kPa pressure

39
Q

Hess's law

A

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

→ the heat change of a reaction is independent to the path followed

40
Q

Law of conservation of energy

A

Energy cannot be created or destroyed but can only be converted to one form of energy into another

41
Q

PRACTICE MATHS

A

42
Q

What are the two main hydrocarbon components of LPG

A

Propane, butane

Chemistry (22 decks)

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