Extracting metals and equilibria Study Guide

Traditional methods for extracting metals from their ores, such as smelting, are often energy-intensive and can lead to significant environmental pollution through the release of sulfur dioxide and carbon dioxide. To address these concerns, alternative biological methods have been developed, specifically bioleaching (using bacteria) and phytoextraction (using plants). These methods offer more sustainable approaches to recover metals, particularly from low-grade ores or contaminated sites. Bioleaching involves using microorganisms to oxidise sulfide minerals or solubilise metal compounds, allowing the metal ions to leach into a solution. Phytoextraction, on the other hand, uses plants that absorb metal ions from the soil through their roots and accumulate them in their biomass. While these biological methods are generally slower than traditional techniques, their environmental advantages and lower operating costs in certain situations make them attractive alternatives, especially for recovering valuable metals or remediating contaminated land.

Ammonia (NH₃) is formed in a chemical reaction between nitrogen (N₂) and hydrogen (H₂) gases. Nitrogen is extracted from the air by fractional distillation, separating it from oxygen and other atmospheric gases. Hydrogen is mainly obtained from natural gas, commonly methane (CH₄), often through a process called steam reforming. In the ammonia synthesis reaction, nitrogen and hydrogen gases combine according to the balanced equation: N₂(g) + 3H₂(g) ↔ 2NH₃(g). The double arrow is significant because it indicates that the reaction is reversible: ammonia can break down to reform nitrogen and hydrogen. Over time, within a closed system, the rates of the forward (formation of ammonia) and reverse (decomposition of ammonia) reactions may become equal. When this occurs, the system is at dynamic equilibrium. At this point, the concentrations of all reactants and products remain constant, even though both reactions continue to occur.