Write a balanced equation for the reaction that occurs in each of the following cases: (a) Potassium metal is exposed to an atmosphere of chlorine gas. (b) Strontium oxide is added to water. (c) A fresh surface of lithium metal is exposed to oxygen gas. (d) Sodium metal reacts with molten sulfur.

The breadcrumbs of chemistry lie in the essence of chemical reactions, which are processes whereby substances, known as reactants, transform into new substances called products. Taking our textbook scenario as an example, potassium metal combining with chlorine gas results in potassium chloride. Here, potassium and chlorine are reactants that, when brought together, undergo a chemical change to form a product.

During these reactions, bonds between atoms break in the reactants and new bonds form in the products. Each reaction has its unique set of reactants and products which vary in properties. In the potassium and chlorine reaction (2K + Cl₂ -> 2KCl), we notice that two individual elements combine to form a compound, which is a typical synthesis reaction.

Understanding chemical reactions is pivotal, as it helps us comprehend how substances interact, predict the outcomes of such interactions, and allows us to use these reactions to our advantage in industrial, pharmaceutical, and other practical applications.

Reaction stoichiometry is like the cookbook for chemists, denoting precise measurements needed to get a perfect chemical dish without leftovers. It revolves around the proportional relationship between reactants and products in a chemical reaction, ensuring the law of conservation of mass is obeyed. When strontium oxide and water combine (SrO + H₂O -> Sr(OH)₂), stoichiometry tells us how much of each reactant is needed to produce a certain amount of product.

By utilizing coefficients, the numbers placed before molecules in a balanced equation, we quantify the number of reacting units. For example, in the reaction of lithium with oxygen (4Li + O₂ -> 2Li₂O), stoichiometry explains that four atoms of lithium react with one molecule of oxygen to form two molecules of lithium oxide.

Grasping reaction stoichiometry is essential for scientists and engineers to design reactions that maximize product yield and for students to predict the outcomes of lab experiments accurately.

The law of conservation of mass is the classical rule dictating that mass cannot be created or destroyed in a closed system, through a chemical reaction. It ensures the quantity of matter remains constant, merely changing forms. In balancing chemical equations, this law is the golden rule.

When we balance an equation, such as that of sodium metal with sulfur (2Na + S -> Na₂S), we are essentially accounting for every atom that participates in the reaction. This process ensures that the mass of the reactants equals the mass of the products, adhering to the law of conservation of mass.

It's the rigorous application of this law that allows us to predict amounts of products and reactants with precision in the lab and in industry, making it a cornerstone principle in the study of chemistry and a fundamental concept for all students to understand fully.