hydrocarbons

• 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