Fuels and Heats of Reaction (Theory)

Organic Chemistry (definition)

Study of the compounds of carbon

Hydrocarbons (definition)

Compounds that contain carbon and hydrogen only

Fossil Fuels (definition)

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

Homologous series (definition)

Series of compounds with similar chemical properties, a general chemical formula and with each successive member differing by CH2

What kind of compounds are alkanes?

Saturated hydrocarbons

What kind of geometry do alkanes have?

Tetrahedral geometry

Saturated compound (definition)

A compound in which there are only single bonds between its atoms

IUPAC name of CH4

Methane

IUPAC name of C2H6

Ethane

IUPAC name of C3H8

Propane

IUPAC name of C4H10

Butane

IUPAC name of C5H12

Pentane

IUPAC name of C6H14

Hexane

IUPAC name of C7H16

Heptane

IUPAC name of C8H18

Octane

IUPAC name of C9H20

Nonane

IUPAC name of C10H22

Decane

Draw methane structural formula

Draw ethane structural formula

What is the general formula of the alkanes?

CnH_2n+2

What solvents are alkanes soluble in?

Non-polar substances e.g. cyclohexane

Why are alkanes insoluble in water?

Non-polar. Only have Van-der-Walls forces between molecules.

C1-C4 are …

Gases

C5-C16 are …

Liquids

C17 and above are …

Waxy solids

Alkanes (boiling points)

Larger molecules have stronger Van-der-Waals forces, increasing their boiling and melting points

Structural isomers (definition)

Compounds that have the same molecular formulae but different structural formulae.

Steps 1 for naming alkanes

Identify longest carbon chain, name the parent molecule

Steps 2 for naming alkanes

Number the carbon chain starting from the end that gives the branches the lowest possible numbers.

CH3 is called what when branching off of a compound?

Methyl

C2H5 is called what when branching off of a compound?

Ethyl

What kind of geometry do alkenes have?

Planar

What kind of compounds are alkenes?

Unsaturated hydrocarbons

Unsaturated compound (definition)

A compound which contains one or more double or triple bonds between its atoms.

IUPAC name for C2H4

Ethene

IUPAC name for C3H6

Propene

IUPAC name for C4H8 if the double bond is between the first and second carbon

But-1-ene

IUPAC name for C4H8 if the double bond is between the second and third carbon

But-2-ene

General formula of alkenes

CnH2n

Are alkenes polar or non-polar and give an example of a solvent?

Non-polar. E.g. cyclohexane

Why are alkenes non-polar?

Large molecules have stronger Van der Waals forces, increasing boiling and melting points

Step 1 for naming alkenes

Identify longest parent carbon chain

Step 2 for naming alkenes

Number the carbons in the molecule starting at the side closest to the double bond. Put position of double bond into name e.g. hex-2-ene

Step 3 for naming alkenes

Indicate type and positions of branching

What is a cyclic hydrocarbon?

When a hydrocarbon’s longest chain of carbon atoms forms a closed ring.

Each point is …

A carbon

Features of cyclohexane

Six carbon atoms, singly bonded in a closed ring.

Features of cyclohexene

Six carbon atoms, with a double carbon bond in a closed ring. The double line represents the double bond

What kind of hydrocarbons are alkynes?

Unsaturated

What kind of bonds do alkynes have?

Triple bonds

What kind of geometry do alkynes have?

Planar geometry

What is the IUPAC name of C2H2 (alkyne)

Ethyne (acetylene)

General formula of alkynes

CnH2n-2

Ethyne and oxygen burn at a very … temperature

High

What compound is ethyne used in and what’s the compound used for?

Oxyacetylene. Welding and cutting metal

What kind of solubles are alkynes soluble in?

Non-polar e.g. cyclohexane

Why are alkynes non-polar?

They only have Van der Waals for es between molecules

Aromatic compounds (definition)

Compounds which contain a benzene ring

Aliphatic compounds (definition)

Open chains and closed chains with no benzene ring

Which is longer, double bonds or single bonds?

Double bonds

Are the bonds in benzene different sizes?

No

Why is there a benzene ring?

Electrons get tossed from carbon to carbon

Examples of aromatic compounds

Benzene, methylbenzene, ethylbenzene

Fractional Distillation (definition)

Used to separate different hydrocarbons into fractions, based on their boiling points

Draw a diagram of fractional distillation/ oil refining

…

Explain fractional distillation

Crude oil heated in furnace and enters bottom of column. High temperature at bottom, low temperature at top. Larger molecules have higher boiling points. Large molecules condense and are collected near the bottom. Smaller molecules condense condense further up the column where it’s cooler.

What does LPG stand for?

Liquified Petroleum Gas

What does LPG consist of and which fraction is it collected in?

Propane and butane. Collected in refinery gases fraction

What is added to LPG?

Mercaptans

What are mercaptans and what are they used for?

Sulphur compounds which give LPG a scent

Where is natural gas found?

Porous rock underground

What does natural gas consist of and what is added to it?

Methane and ethane. Mercaptans are added for odour

Octane number (definition)

Of a fuel is a measure of its tendency to resist autoignition

Different terms for autoignition (2)

Knocking/ pinking

Autoignition (definition)

The premature ignition of a fuel-air mixture

What does a fuel with a low octane number cause?

Causes wear on the engine. Loss of power

What hydrocarbon has the lowest/ worst octane number?

Heptane

What hydrocarbon has the highest/ best octane number?

2,2,4-trimethylpentane

What does “Octane 95” mean on a fuel pump?

The fuel has the same tendency to auto ignite as a mixture of 95% 2,2,4-trimethylpentane and 5% heptane

Three factors that affect octane number

Length of chain, degree of branching, presence of rings

How does chain length affect the octane number?

Shorter carbon chains have higher octane numbers

How does degree of branching affect octane number?

The more branching a hydrocarbon has, the higher the octane number

How does the presence of rings affect octane number?

Ring structures give fuels higher octane numbers. Benzene rings have even higher octane numbers

Name the processes which raise the octane number of a fuel (5)

Isomerisation. Catalytic cracking. Dehydrocyclisation. Adding oxygenates. Addition of lead

What is isomerisation?

Changing straight chain alkanes into their branched isomers to raise octane number

What is catalytic cracking?

Uses heat and a catalyst to break down long hydrocarbons into an alkene and a shorter alkane since they have higher octane numbers

What is dehydrocyclisation?

Uses catalysts to change linear molecules into cyclic molecules or cyclic molecules into aromatic compounds. Hydrogen gas is formed

What is adding oxygenates?

The addition of oxygen-containing compounds to a fuel to raise its octane number

What is an extra benefit of adding oxygenates to fuels other than to raise octane numbers?

Makes fuel release less carbon dioxide when burnt

What is the addition of Lead

Adding lead compounds to petrol to increase octane number

Examples of oxygenates

Methanol. Ethanol. MTBE

What does MTBE stand for?

Methyl Tertiary-Butyl Ether

Name a lead compound

Tetraethyl lead

Why was lead banned in petrol?

It’s a poisonous health hazard. Poisons the metals in a car’s catalytic converter. That’s why petrol pumps say “Unleaded”

When was the addition of lead banned?

2000

What are the two ways to produce hydrogen gas for use as a fuel?

Steam reforming of natural gas. Electrolysis of water.

How does “steam reforming of natural gas” work?

Steam is reacted with natural gas using a catalyst

Steam reforming of natural gas (equation)

CH4 + H2O → 3H2 + CO

How does “Electrolysis of Water” work? What is its disadvantage?

Electric current is passed through water. This method is too expensive to be practical.

Electrolysis of Water (equation)

H2O → H2 + 1/2O2