the homologous series is a family of molecules with the same general formula and similar chemical properties
they differ by CH2
the bigger the molecule the higher the boiling point
examples of homologous series of hydrocarbons are alkanes and alkenes
the size of hydrocarbons determine their properties e.g the size of hydrocarbon determines which fraction of crude oil it separates into
physical properties are determined by intermolecular forces
in small molecule intermolecular forces break more easily as they are much weaker than in big molecules
small molecules have lower melting points and boiling points compared to large ones
short hydrocarbons ignite easier as they have lower boiling points and are mostly gasses at room temperature. the gas mixes with oxygen to form a gas mixture which burns into flames
viscosity: how easily something flows. stronger forces between long hydrocarbons mean it's harder for the liquid to flow so fractions have a higher viscosity
they create exothermic reactions as they act as great fuels due to combustion reactions when burnt with oxygen releasing lots of energy
complete combustion -all the hydrocarbons are oxidised to form carbon dioxide and water. incomplete combustion-hydrocarbons are burnt on a limited supply of oxygen