One of the simplest metals to extract from its ores is mercury. Mercury vapor is produced by roasting cinnabar ore (HgS) in air. Alternatives to this simple roasting, designed to reduce or eliminate \(\mathrm{SO}_{2}\) emissions, is to roast the ore in the presence of a second substance. For example, when cinnabar is roasted with quicklime, the products are mercury vapor and calcium sulfide and calcium sulfate. Write equations for the two reactions described here.

Chemical reactions are the processes by which substances combine or break apart to form new substances. Each reaction involves reactants that undergo a change to become the products. In the context of extracting mercury, two different types of reactions are mentioned: roasting cinnabar ore in air and roasting cinnabar with quicklime.

Roasting cinnabar in the presence of air is a type of oxidation reaction, where cinnabar (HgS) reacts with oxygen (O2) to produce mercury vapor (Hg) and sulfur dioxide (SO2). This reaction is significant for it not only yields mercury but also a potentially harmful byproduct, SO2, which contributes to environmental pollution.

The alternative method described involves roasting cinnabar with quicklime (CaO), which is an example of a chemical reaction that results in multiple products: mercury vapor, calcium sulfide (CaS), and calcium sulfate (CaSO4). This method is designed to reduce SO2 emissions by incorporating it into other less harmful products.

Balancing chemical equations is essential in ensuring the law of conservation of mass is upheld; the mass of the reactants must equal the mass of the products. To balance an equation, one must make sure the number of atoms of each element is the same on both sides.

In the solution provided, the first reaction, involving the roasting of cinnabar in air, was already balanced: the reactants HgS and O2 yield the products Hg and SO2 with no need for additional coefficients.

However, the second reaction required adjusting the coefficients to achieve balance. The starting, unbalanced equation for the reaction of cinnabar with quicklime was: \(HgS + CaO \rightarrow Hg + CaS + CaSO4\). With the coefficients added, the balanced form became: \(2HgS + 2CaO \rightarrow 2Hg + CaS + CaSO4\), ensuring the same number of each type of atom on both sides of the equation. Balancing chemical equations is not only a mathematical exercise but also a fundamental principle of understanding and predicting the outcomes of chemical reactions.

The cinnabar roasting process is a method used to extract mercury from its ore—cinnabar (HgS). Roasting refers to heating the ore in the presence of air or another substance, which triggers a chemical reaction that releases mercury as a vapor.

The traditional roasting process involves heating cinnabar in air, leading to the formation of mercury vapor and sulfur dioxide, as represented by the equation: \(HgS + O2 \rightarrow Hg + SO2\). This process, while straightforward, presents environmental concerns due to the emission of SO2, a noxious gas that can lead to acid rain and respiratory problems.

To mitigate these effects, an alternative method, known as the lime roasting process, incorporates quicklime (CaO) as an additional reactant. The presence of quicklime allows the capture of sulfur in the form of less harmful compounds such as calcium sulfide and calcium sulfate, as seen in the balanced reaction: \(2HgS + 2CaO \rightarrow 2Hg + CaS + CaSO4\). This reduces SO2 emissions, making the process more environmentally friendly. Understanding the cinnabar roasting process is crucial for both obtaining mercury and developing sustainable industrial practices.