LC CHEMISTRY -FUELS AND HEATS

REBECCA OMOSEBI'S LC CHEMSITRY FUELS AND HEATS KNOWT

Organic Chemistry

the study of the compounds of carbon

Hydrocarbon

a compound that contains carbon and hydrogen only

Sources of Hydrocarbons

coal, natural gas (methane), petroleum (crude oil)

Fossil Fuels

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

Alkanes

a family of hydrocarbons in which all the atoms are linked by single bonds

Saturated Compound

a compound in which there are only single bonds between the atoms in the molecules

Methane

CH4

Ethane

C2H6

Propane

C3H8

Butane

C4H10

Pentane

C5H12

Hexane

C6H14

Heptane

C7H16

Octane

C8H18

Nonane

C9H20

Decane

C10H22

Properties of Alkanes and Alkenes

soluble in non-polar solvents like cyclohexane; insoluble in water; only have Van der Waals forces between molecules; larger molecules have stronger Van der Waals forces, increasing boiling and melting points

Homologous Series

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

Structural Isomers

compounds with the same molecular formula but different structural formulas

Methyl Group

CH3

Ethyl Group

C2H5

Propyl Group

C3H7

Alkenes

contain one carbon-carbon double bond between two carbons in the molecule

Unsaturated Compound

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

Alkynes

contain a carbon-carbon triple bond

Aliphatic Compound

an organic compound that consists of open chains of carbon atoms and closed chain compounds (rings) resembling them in chemical properties

Aromatic Compounds

compounds that contain a benzene ring structure in their molecules

Benzene Ring

C6H6

Fractional Distillation

a process used to separate crude oil into fractions based on boiling points

Refinery Gas

bottled gas

Gasoline

used as fuel for cars

Naphtha

used to make chemicals

Kerosene

used as fuel for aircrafts

Diesel

used as fuel for cars, lorries, and buses

Fuel Oil

used as fuel for ships and power stations

Residue

used as bitumen for roads and roofs

Liquid Petroleum Gas (LPG)

consists of butane and propane, used in cooking

Mercaptans

sulphur compounds added to LPG to give it a smell for leak detection

Auto Ignition

premature ignition (explosion) of the petrol-air mixture before normal ignition by a spark

Octane Number

a measure of the tendency of a fuel to resist knocking (autoignition)

2,2,4-trimethylpentane

octane number 100, low tendency to auto-ignite due to branching

Heptane

octane number 0, auto-ignites readily

Factors Affecting Octane Number

length of chain, degree of branching, straight-chain or cyclic structure

Length of Chain

shorter chain = higher octane number

Degree of Branching

more branching = higher octane number

Straight Chain or Cyclic Structure

cyclic compounds = higher octane number

Increasing Octane Number

isomerisation, catalytic cracking, dehydrocyclisation, adding oxygenates

Isomerisation

changes straight-chain alkanes into their isomers

Catalytic Cracking

breaking down long-chain hydrocarbons into short-chain molecules using heat and catalysts

Dehydrocyclisation

use of catalysts to form ring compounds

Adding Oxygenates

methanol, ethanol, and MTBE increase octane number and reduce pollution

MTBE

Methyl Tertiary-Butyl Ether

Production of Hydrogen

by electrolysis of water or steam reforming of natural gas

Steam Reforming

reacting steam with natural gas using a catalyst (CH4 + H2O → 3H2 + CO)

Electrolysis of Water

electric current passed through water (H2O → H2 + ½O2)

Uses of Hydrogen

produce ammonia (NH3), hydrogenate vegetable oils, burn as a fuel

Hydrogen Safety

forms explosive mixtures with air, difficult to store and transport safely

Exothermic Reaction

produces heat; ΔH is negative

Endothermic Reaction

absorbs heat; ΔH is positive

Heat of Reaction (ΔH)

heat change when reactants in the balanced equation react completely

Heat of Combustion (ΔH)

heat change when one mole of a substance is burned completely in excess oxygen

Bomb Calorimeter

instrument for measuring heats of combustion

Kilogram Calorific Value

heat energy produced when 1kg of fuel burns in oxygen

Bond Energy

average energy required to break one mole of a covalent bond

Heat of Neutralisation

heat change when one mole of H+ reacts with one mole of OH−

Heat of Formation

heat change when one mole of a compound is formed from its elements in their standard states

Hess’s Law

sum of heat changes in stages = heat change if reaction occurs in one stage

Law of Conservation of Energy

energy cannot be created or destroyed, only converted from one form to another

Alkanes Shape

tetrahedral

First Ten Alkanes

Methane, Ethane, Propane, Butane, Pentane, Hexane, Heptane, Octane, Nonane, Decane

General Formula of Alkanes

CnH2n+2

Naming Alkanes

count carbons, indicate branches, use commas between numbers and dashes between words

Saturated Compound

only single bonds

Alkenes

contain double bond between two carbons; unsaturated hydrocarbons

Planar Geometry

for alkenes

Naming Alkenes

count carbons, number from end nearer to double bond, indicate branches

Cyclohexane

single bond hydrocarbon

Cyclohexene

double bond hydrocarbon

Alkynes

triple bond between two carbons; unsaturated hydrocarbons

Ethyne

IUPAC name for acetylene (C2H2)

General Formula of Alkynes

CnH2n-2

Use of Ethyne

welding and cutting metal

Crude Oil

made of different hydrocarbons

Fractional Distillation

separates hydrocarbons based on boiling points

Heat of Combustion Measured Using

a bomb calorimeter

Steps in Bomb Calorimeter

process: ignite sample, heat spreads, temperature measured

Balancing Heat of Combustion Equation

make fuel = 1 mole, balance other elements