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prop-of-alkanes-to-aromatic-compounds.docx - Properties of...

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Properties of AlkanesPhysical PropertiesPhysical stateoC1 = major source of natural gasNatural gas – primarily methane but also includes some of the other gaseous alkanesoC2 = minor source of natural gasoC3 = bottled gas (propane)oC4 = lighter gas (butane)oGasoline includes all alkaneswith 5 – 12 carbon atomsoKerosene contains those with 12 – 15 carbon atomsoHome heating oil fuels – contain those with 15 – 18 carbon atomsBoiling Points-Boiling point depends on the attractive forces operating between their molecules-The boiling points of alkanes increase with increase of number of carbon atomsoWith the increase in the number of carbon atoms, the molecule becomes big and the surface area of themolecule increases and thereby Van derWaals force of attraction also increases resulting in an increasein boiling points-Branched chain alkanes have lower boiling points compared to their straight counterpartsMelting points-Melting points of alkanes with even number of carbon atoms are more than those with odd number of carbonsoAlkanes with even number of carbon atoms can be closely and effectively packed in the solid state thanthe alkanes with odd number of carbon atomsoSuch closed packing leads to higher melting point-But if we consider the variation of melting point of straight chain alkanes with even number of carbon atoms orodd number of carbon atoms separately we will find that melting point increases regularly with increase innumber of carbon atomsAlkaneC3H8C5H12C7H16C9H20Melting point (K)83.1142.6193.1222.1AlkaneCH4C2H6C4H10C6H14C8H18C10H22Melting point(k)83.1142.6193.1222.1216.6241.1Solubility-Covalent bonds in alkanes are slightly polar because electronegativity of H and C are close-Alkanes are non-polar compounds, so they are not soluble in polar solvents like water, but soluble in each otherand in non-polar solvents like chloroform and carbon tetrachlorideDensity-Substances which have high molecular weight have densities that tends to be higher than those low molecularweight-The densities of alkanes increase with the increase in number of carbon atoms due to increase in molecularweight-Density of solid and liquid alkanes = 0.6 g/cm3– 0.8 g/cm3-In general, liquid and solid alkanes are lighter than waterChemical Properties-Categories of ReactionsoOxidationoSubstitutionoEliminationoAddition
I. Oxidation-Alkanes are quite inert toward common oxidizing agents and do not decolorize alkaline KMnO4, nor do they reactwith acids and bases-However, when burnt in excess of air, alkanes are completely oxidized to CO2and water with the evolution ofheatoViolent explosions occur only when their vapours mix with air in the presence of spark-Reaction is exothermicoTo produce heat energy, all alkanes give off heat during burning. We power our automobile engines byburning alkanes of 6-12 carbon atoms. In engines, the expansion of hot gases causes pistons to move intheir cylinders thus converting chemical energy of gasoline into mechanical energyo

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Term
Fall
Professor
Evelyn Sebastian
Tags
Methane

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