Global challenges Study Guide

Condensation polymerisation is a type of polymerisation reaction where monomer molecules join together to form a larger polymer molecule, with the simultaneous elimination of a small molecule, usually water. Unlike addition polymerisation, which requires monomers with carbon-carbon double bonds, condensation polymerisation utilises monomers that have at least two different functional groups capable of reacting with each other. For example, a dicarboxylic acid (containing two -COOH groups) can react with a diamine (containing two -NH2 groups) to form a polyamide. Similarly, a dicarboxylic acid can react with a diol (containing two -OH groups) to form a polyester. Each functional group on one monomer reacts with a functional group on another monomer, forming a new covalent bond and releasing a small molecule (often H2O, but sometimes HCl or NH3). This process continues, linking many monomer units into a long chain polymer. The resulting polymer chain contains repeating units that are structurally different from the original monomers because parts of the functional groups have been removed.

The atmosphere contains various gases and particles that can have harmful effects when their concentrations increase. Key pollutants include carbon monoxide, sulfur dioxide, oxides of nitrogen, and particulates. Carbon monoxide (CO) is a toxic gas produced by the incomplete combustion of fossil fuels, primarily from vehicle exhausts and poorly ventilated household appliances. It is dangerous because it binds to haemoglobin in red blood cells more readily than oxygen, reducing the blood's capacity to transport oxygen, leading to headaches, dizziness, and even death. Sulfur dioxide (SO2) largely originates from the combustion of fossil fuels (especially coal) that contain sulfur impurities, typically in power stations. When SO2 dissolves in atmospheric water vapour, it forms sulfuric acid, contributing significantly to acid rain. Acid rain corrodes buildings, damages aquatic ecosystems, and harms vegetation. Oxides of nitrogen (NOx), particularly nitrogen monoxide (NO) and nitrogen dioxide (NO2), are formed in high-temperature combustion processes, such as car engines and power stations, where nitrogen and oxygen from the air react. NO2 also contributes to acid rain and respiratory problems, and it plays a role in forming photochemical smog, which irritates the eyes and lungs. Particulates are tiny solid particles or liquid droplets suspended in the air, often produced by burning fossil fuels and biomass (e.g., diesel engines, wood fires). They can cause respiratory issues like asthma and bronchitis, reduce visibility, and lead to early deaths. Large particulates settle out of the atmosphere quicker; however, smaller particulates can remain suspended for long periods, travelling significant distances and contributing to haze and reduced air quality across regions.