For the reaction shown, calculate how many grams of oxygen form when each quantity of reactant completely reacts. $$ 2 \mathrm{HgO}(\mathrm{s}) \longrightarrow 2 \mathrm{Hg}(l)+\mathrm{O}_{2}(g) $$ (a) \(2.13 \mathrm{~g} \mathrm{Hg} \mathrm{O}\) (b) \(6.77 \mathrm{~g} \mathrm{Hg} \mathrm{O}\) (c) \(1.55 \mathrm{~kg} \mathrm{Hg} \mathrm{O}\) (d) \(3.87 \mathrm{mg} \mathrm{HgO}\)

Molar mass is defined as the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It plays a crucial role in stoichiometry calculations because it allows for the conversion between mass and moles of a substance. To calculate molar mass, you simply add up the atomic masses of all the atoms in the chemical formula of a substance.

For instance, in our exercise, the molar mass of mercury(II) oxide (HgO) is found by adding the atomic mass of mercury (200.59 g/mol) to the atomic mass of oxygen (16 g/mol), resulting in a molar mass of 216.59 g/mol. This calculation is the foundation for all subsequent steps in converting grams of HgO to grams of oxygen gas (O₂).

Chemical reactions are processes where reactants transform into products through the breaking and formation of chemical bonds. Writing and balancing chemical equations are pivotal to understanding these reactions. The balanced equation ensures that the law of conservation of mass is followed, meaning the number of atoms of each element is the same on both sides of the equation.

In the reaction from the given exercise, mercury(II) oxide decomposes into liquid mercury and oxygen gas when heated. This reaction is represented by the balanced equation:
2 HgO(s) → 2 Hg(l) + O₂(g).

It illustrates that two moles of HgO produce one mole of oxygen gas. This ratio is used to calculate how much oxygen is formed from a given amount of HgO.

Stoichiometric coefficients are the numbers written in front of the reactants and products in a balanced chemical equation, representing the ratio in which substances react and are produced. These coefficients are the key to converting between moles of different substances in a reaction.

In our example, the stoichiometric coefficients indicate that for every two moles of HgO that react, one mole of O₂ is produced. Understanding the ratio provided by these coefficients allows you to perform the stoichiometry calculations accurately, ensuring you use the correct proportion of reactants to predict the yield of products.

Mole-to-mass conversion is a technique utilized to convert the number of moles of a substance to its mass in grams, and vice versa, using its molar mass. Once you have the number of moles from the balance equation, you multiply it by the molar mass to get mass.

For part (a) of the exercise, the number of moles of oxygen gas formed is 0.004918 moles. This number is found using the stoichiometric coefficients of the balanced equation. By multiplying the moles of O₂ (0.004918 moles) by its molar mass (32.00 g/mol), you find that the mass of O₂ formed from 2.13 g of HgO is 0.157 grams.