Question

Write a balanced equation for the reaction that occurs in each of the following cases: (a) Potassium metal burns in 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 is reacted with molten sulfur.

Short answer

(a) 2K + Cl2 → 2KCl (b) SrO + H2O → Sr(OH)2 (c) 4Li + O2 → 2Li2O (d) 2Na + S → Na2S

Step-by-step solution

(a) Potassium metal burns in an atmosphere of chlorine gas.

Reactants: Potassium metal (K) and chlorine gas (Cl2) Reaction: Potassium metal reacts with chlorine gas to form potassium chloride (KCl). Unbalanced Equation: K + Cl2 → KCl To balance the equation, place a coefficient of 2 in front of KCl: Balanced Equation: 2K + Cl2 → 2KCl

(b) Strontium oxide is added to water.

Reactants: Strontium oxide (SrO) and water (H2O) Reaction: Strontium oxide reacts with water to form strontium hydroxide (Sr(OH)2). Unbalanced Equation: SrO + H2O → Sr(OH)2 To balance the equation, place a coefficient of 2 in front of H2O since there are two hydroxide ions, and place a coefficient of 1 in front of SrO: Balanced Equation: SrO + H2O → Sr(OH)2

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

Reactants: Lithium metal (Li) and oxygen gas (O2) Reaction: Lithium metal reacts with oxygen gas to form lithium oxide (Li2O). Unbalanced Equation: Li + O2 → Li2O To balance the equation, place a coefficient of 4 in front of Li and a coefficient of 2 in front of Li2O: Balanced Equation: 4Li + O2 → 2Li2O

(d) Sodium metal is reacted with molten sulfur.

Reactants: Sodium metal (Na) and molten sulfur (S) Reaction: Sodium metal reacts with molten sulfur to form sodium sulfide (Na2S). Unbalanced Equation: Na + S → Na2S To balance the equation, place a coefficient of 2 in front of Na: Balanced Equation: 2Na + S → Na2S

Key concepts

Chemical Reactions

At the heart of chemistry lies the study of chemical reactions, processes in which substances, known as reactants, are transformed into different substances called products. These reactions involve the breaking and forming of bonds between atoms.

Reactants undergo transformations to become products through various reaction types, such as synthesis, decomposition, single replacement, and double replacement reactions. The reaction type dictates how atoms are rearranged. For instance, when potassium metal burns in chlorine gas, we observe a synthesis reaction where potassium and chlorine combine to form potassium chloride. This process can be represented by a chemical equation that illustrates the conversion of reactants to products.

Importance of Reaction Types

In understanding how to balance chemical equations, recognizing the reaction type helps in predicting the products of the reaction and guides the balancing process. For instance, when lithium metal is exposed to oxygen gas, a synthesis reaction occurs, producing lithium oxide as the product. The correct representation of these changes is crucial for experimenting with, predicting, and understanding reaction outcomes.

Stoichiometry

Stoichiometry is a branch of chemistry that quantitatively describes the relationships between reactants and products in a chemical reaction. It is based on the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction.

When balancing chemical equations, stoichiometry comes into play by ensuring that the number of atoms for each element is equal on both sides of the equation. It enables us to predict the quantities of substances consumed and produced in a reaction. For example, when sodium metal reacts with molten sulfur, stoichiometry dictates the ratio of sodium atoms to sulfur atoms in the products, which guides the placement of coefficients to achieve a balanced equation.

Real-World Applications

The principles of stoichiometry are applicable in everyday life, from cooking recipes to pharmaceutical dosing, and industrial manufacturing processes. It is an essential tool for chemists who need to scale up reactions for production, ensure safety in handling chemicals, and optimize resources.

Reactants and Products

The substances that undergo change in a chemical reaction are known as reactants, and the substances that are formed as a result of this change are called products. The nature of reactants and products is fundamental to chemical equations, where reactants are listed on the left-hand side and products on the right-hand side.

Different reactants have varying reactivities, and understanding their properties is crucial for predicting the outcomes of reactions. For example, when strontium oxide is added to water, it reacts to form strontium hydroxide through a process known as a reaction with water or hydrolysis, showcasing the reactivity of strontium oxide as a base.

Manipulating Reactants and Products

Learning to manipulate the amounts of reactants and products in a balanced equation is a fundamental skill in chemistry. It allows scientists to control the direction and yield of a reaction and to generate desired products efficiently. The practice of balancing chemical equations trains students to see reactants and products not just as individual chemicals but as parts of an interconnected process governed by stoichiometric principles.