Question

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.

Short answer

(a) \(2K + Cl_2 -> 2KCl\) (b) \(SrO + H_2O -> Sr(OH)_2\) (c) \(4Li + O_2 -> 2Li_2O\) (d) \(2Na + S -> Na_2S\)

Step-by-step solution

(a) Potassium metal is exposed to an atmosphere of chlorine gas.

When potassium (K) reacts with chlorine gas (Cl2), the product is potassium chloride (KCl). To balance the equation, we need to make sure there are an equal number of potassium and chlorine atoms on both sides. The balanced chemical equation can be written as: 2K + Cl₂ -> 2KCl

(b) Strontium oxide is added to water.

When strontium oxide (SrO) reacts with water (H2O), the resulting products are strontium hydroxide (Sr(OH)2). To balance this equation, let's consider the number of atoms in the reactants and the products. The balanced chemical equation is: SrO + H₂O -> Sr(OH)₂

(c) A fresh surface of lithium metal is exposed to oxygen gas.

Lithium (Li) reacts with oxygen gas (O2) to form lithium oxide (Li2O). To balance this equation, we need to ensure there are equal numbers of lithium and oxygen atoms on both sides of the equation. The balanced chemical equation for this reaction is: 4Li + O₂ -> 2Li₂O

(d) Sodium metal reacts with molten sulfur.

When sodium (Na) reacts with sulfur (S), it forms sodium sulfide (Na2S). We need to balance the equation for this reaction by considering the number of sodium and sulfur atoms present. The balanced chemical equation for this reaction is: 2Na + S -> Na₂S

Key concepts

Chemical Reactions

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

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.

Law of Conservation of Mass

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.