Summary
Highlights
Alkanes undergo two main types of reactions: combustion (complete combustion yields CO2 and water) and substitution (e.g., methane reacts with chlorine in sunlight to produce chloromethane and HCl). Substitution reactions often yield a mixture of products. Alkenes undergo combustion and addition reactions. In addition reactions, the double bond breaks, and additional atoms are incorporated into the molecule (e.g., ethene with bromine yields 1,2-dibromoethane, resulting in a color change from brown to colorless, indicating unsaturation).
Organic chemistry focuses on compounds containing carbon. Hydrocarbons, the simplest organic compounds, contain only hydrogen and carbon. They are categorized as saturated (alkanes, single bonds) or unsaturated (alkenes, double bonds). Alkanes have the general formula CnH2n+2, while alkenes have CnH2n. Examples include methane, ethane, propane, and butane for alkanes, and ethene, propene, and butene for alkenes. Alkenes require at least two carbon atoms to form a double bond.
Alcohols are organic compounds containing a hydroxyl group (-OH) with the general formula CnH2n+1OH. Examples include methanol, ethanol, propanol, and butanol. Carboxylic acids contain a carboxyl group (-COOH) with the general formula CnH2n+1COOH. Examples are methanoic acid, ethanoic acid, propanoic acid, and butanoic acid. Functional groups, such as the double bond in alkenes, the hydroxyl group in alcohols, and the carboxyl group in carboxylic acids, are the sites of chemical reactions.
Isomerism occurs when compounds have the same molecular formula but different structural formulas and therefore different properties. Examples include ethanol and methoxymethane (C2H6O). Different isomers can exist for alkanes (e.g., pentane, 2-methylbutane, 2,2-dimethylpropane) and alkenes (e.g., but-1-ene, but-2-ene, 2-methylprop-1-ene). A homologous series is a family of organic compounds with similar chemical properties, the same general formula, and successive members differing by a CH2 group. They show a gradual change in physical properties.
Ethanol can be produced via two main methods. Fermentation involves converting glucose into ethanol and carbon dioxide using yeast at 37°C. It's a cheaper process using renewable resources but is slow and produces impure ethanol. Hydration of ethene involves reacting ethene with steam (H2O) at 300°C, 60 atm pressure, and a phosphoric acid catalyst. This method yields pure ethanol, is a continuous process, and produces no greenhouse gases, but uses non-renewable raw materials and is expensive due to high energy requirements.
Alcohols can undergo oxidation to form carboxylic acids (e.g., ethanol oxidizes to ethanoic acid). Strong oxidizing agents like acidified potassium manganate can be used. Alcohols also undergo complete combustion, producing carbon dioxide and water. Carboxylic acids are weak acids and react with metals (to produce a salt and hydrogen gas), bases/alkalis (to produce a salt and water), and carbonates (to produce a salt, water, and carbon dioxide).
Esters are formed in a reaction between an alcohol and a carboxylic acid, releasing water (esterification). The ester name is derived from the alcohol (alkyl group) and the carboxylic acid (alkanoate group), for example, ethanol and ethanoic acid form ethyl ethanoate. Esters contain an ester linkage (C=O-O). Hydrolysis is the reverse process, where an ester is broken down back into an alcohol and a carboxylic acid by adding water, often in the presence of H+ or OH- ions.
Fuels are substances that release energy upon burning (e.g., coal, petroleum, natural gas). Fractional distillation is a separation technique for liquids with different boiling points, commonly used for crude oil. Fractions at the top of the column have lower boiling points, lower viscosity, and higher volatility, while those at the bottom have higher boiling points, higher viscosity, and lower volatility.
Polymers are large molecules formed by linking many smaller monomer units. Polymerization is the process of forming polymers. In addition polymerization, monomers with double bonds link together after the breakage of the double bond (e.g., ethene forms poly(ethene)). Common addition polymers include PVC and Teflon. The advantages of plastic include being non-reactive, lightweight, water-resistant, and durable, while disadvantages include being non-biodegradable, produced from non-renewable sources, and causing toxic gases when burnt. Disposal options include reducing usage, recycling, and safe disposal methods.
Condensation polymerization involves the removal of a small molecule, like water, as monomers combine. Examples include nylon (formed from diamine and dicarboxylic acid, forming an amide linkage), Terylene (formed from ethene-1,2-diol and benzene-1,4-dicarboxylic acid, forming an ester linkage), and naturally occurring polymers like starch (from glucose monomers) and proteins (from amino acid monomers). Proteins are polyamides, containing many amide linkages. Amino acids are identified using chromatography and contain both an amine group and a carboxyl group, linked by an 'R' group variable.
Cracking is the process of breaking down large, complex hydrocarbons into smaller, simpler ones. This typically occurs at high temperatures (500°C) and with catalysts (Al2O3 or Cr2O3). Cracking conserves natural resources and can produce a mixture of alkanes and alkenes, and sometimes hydrogen gas.