Nylon 6,6 may be formed by means of a condensation polymerization reaction in which hexamethylene diamine \(\left[\mathrm{NH}_{2}-\left(\mathrm{CH}_{2}\right)_{6}-\right.\) \(\left.\mathrm{NH}_{2}\right]\) and adipic acid react with one another with the formation of water as a byproduct. What masses of hexamethylene diamine and adipic acid are necessary to yield \(20 \mathrm{kg}\) of completely linear nylon \(6,6 ?\) (Note: the chemical equation for this reaction is the answer to Concept Check \(15.12 .\) )

When we explore the creation of materials like Nylon 6,6, we delve into the fascinating world of condensation polymerization, a chemical reaction where monomers link together, losing small molecules as byproducts, often water. This particular polymerization is like constructing a train by joining carriages end-to-end, each time releasing a puff of steam. In the Nylon 6,6 synthesis, hexamethylene diamine and adipic acid are the 'carriages' forming a polymer chain and releasing water.

The beauty of this process is that it's methodical, linking one monomer unit after another, building up a large molecule, or polymer, that has repeating structural units. To envision this, imagine a zipper where each monomer is a tooth, and as it pulls together, something small separates, signifying the condensation aspect of the reaction.

The term stoichiometry is derived from the Greek words for 'element' and 'measure,' and it's a way to quantify relationships within a chemical reaction. It operates on the principle of conservation of mass where the mass of the reactants equals the mass of the products. To relate this to a kitchen recipe, think about how many eggs and how much flour you'd need to make a cake – that’s stoichiometry in action.

In our Nylon 6,6 example, we treated stoichiometry as our recipe book, letting us calculate the exact amounts of hexamethylene diamine and adipic acid required to produce a specific mass of nylon. Since the chemical equation is balanced with a 1:1 molar ratio, it operates like a precise cooking recipe ensuring we use each ingredient in just the right amount to get our desired product.

When we measure out our ingredients in chemistry, we're not using cups and teaspoons, but rather a scale called molecular weight, which essentially tells us the 'weight' of a formula unit of a substance. Seeing molecular weight as a bridge, it allows us to convert between the mass of a substance and the number of moles, which represents the count of molecules.

Calculating the molecular weight is akin to tallying up the weight of each atom in a molecule, based on the atomic weights found on the periodic table. For the Nylon 6,6 synthesis, we calculated the molecular weight of each reactant and the polymer to determine how many grams of each reactant are needed to result in a targeted mass of the final polymer. It's a lot like calculating how much of each type of fruit you need to get a pound of fruit salad.