Fifteen kilograms of polychloroprene is vulcanized with \(5.2 \mathrm{~kg}\) of sulfur. What fraction of the possible crosslink sites is bonded to sulfur crosslinks, assuming that, on the average, \(5.5\) sulfur atoms participate in each crosslink?

Crosslinking in polymer science is a chemical process where individual polymer chains are linked together to form a three-dimensional network. This process can significantly alter the physical properties of the original polymer, often leading to increased strength, elasticity, and durability. Traditional rubber, for example, becomes less sticky and more durable after vulcanization, which is a form of crosslinking. During the vulcanization of polychloroprene, sulfur atoms act as a bridge between polymer chains, creating crosslinks.

In the case of vulcanization, the amount of sulfur used and the number of sulfur atoms that participate in each crosslink are critical factors that determine the extent of crosslinking. The practical consequence of these crosslinks is evident in products like car tires, where improved mechanical properties are essential for performance and safety.

Understanding how to calculate moles is a foundation in chemistry that allows us to measure quantities of substances based on their molecular weights. Moles provide a bridge between the microscopic world of atoms and molecules and the macroscopic world of grams and kilograms that we can measure in the lab. The mole concept is vital in stoichiometry as it enables chemists to predict how much of a substance will react with another.

The number of moles of a substance is calculated by dividing the mass of the substance (in grams) by its molecular weight (in grams per mole). In the context of our exercise, by determining the moles of polychloroprene and sulfur, we can deduce how they react during the vulcanization process. By knowing the number of moles, we can predict the extent of crosslinking and ultimately, the properties of the final vulcanized product.

Determining the molecular weight of a substance is crucial for various calculations in chemistry, including the computation of moles. Molecular weight, also called molecular mass, is the sum of the atomic weights of all atoms in a molecule. It is generally expressed in units of grams per mole (g/mol).

For polymers like polychloroprene, the repeating unit's molecular weight is calculated by adding the atomic weights of each constituent atom. In our exercise, we use the molecular weight of polychloroprene and sulfur to find out how many moles of each are present. Accurate determination of molecular weights is essential because it affects the stoichiometry of chemical reactions and the properties of materials, which, in turn, impacts how substances interact in a given application, such as in the vulcanization of rubber.