Problem 73 - Chemistry Central Science

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.

Step-by-Step Solution

Answer

The short answers for the balanced equations are: a) 2K + Cl2 → 2KCl b) SrO + H2O → Sr(OH)2 c) 4Li + O2 → 2Li2O d) 16Na + S8 → 8Na2S

Step 1: Identify the reactants and products

In this reaction, potassium metal (K) reacts with chlorine gas (Cl2) to form potassium chloride (KCl).

Step 2: Write the unbalanced equation

K + Cl2 → KCl

Step 3: Balance the equation

To balance the equation, we adjust the coefficients to make the number of atoms of each element the same on both sides. The balanced equation is: 2K + Cl2 → 2KCl b) Strontium oxide is added to water. (Acid-Base Reaction)

Step 1: Identify the reactants and products

In this reaction, strontium oxide (SrO) reacts with water (H2O) to form strontium hydroxide (Sr(OH)2).

Step 2: Write the unbalanced equation

SrO + H2O → Sr(OH)2

Step 3: Balance the equation

The equation is already balanced, so there is no need to adjust the coefficients. The balanced equation is: SrO + H2O → Sr(OH)2 c) A fresh surface of lithium metal is exposed to oxygen gas. (Combination Reaction)

Step 1: Identify the reactants and products

In this reaction, lithium metal (Li) reacts with oxygen gas (O2) to form lithium oxide (Li2O).

Step 2: Write the unbalanced equation

Li + O2 → Li2O

Step 3: Balance the equation

To balance the equation, we adjust the coefficients to make the number of atoms of each element the same on both sides. The balanced equation is: 4Li + O2 → 2Li2O d) Sodium metal is reacted with molten sulfur. (Combination Reaction)

Step 1: Identify the reactants and products

In this reaction, sodium metal (Na) reacts with molten sulfur (S8) to form sodium sulfide (Na2S).

Step 2: Write the unbalanced equation

Na + S8 → Na2S

Step 3: Balance the equation

To balance the equation, we adjust the coefficients to make the number of atoms of each element the same on both sides. The balanced equation is: 16Na + S8 → 8Na2S

Key Concepts

Balanced Equations

A balanced chemical equation is crucial for properly representing a chemical reaction. It follows the Law of Conservation of Mass, which states that in any chemical reaction, matter is neither created nor destroyed. This means the number of atoms for each element must be the same on both sides of the equation.

To achieve a balanced equation:

• Identify all reactants and products in the unbalanced equation.
• Count the number of each type of atom on both sides of the equation.
• Adjust coefficients (numbers placed before compounds) to balance atoms for each element.
• Always double-check to ensure all elements are balanced.

Remember, balancing an equation does not alter the compounds' chemical nature but ensures that the same amount of each element is accounted for before and after the reaction.

Acid-Base Reactions

Acid-base reactions are a fascinating type of chemical reaction. They involve the transfer of protons (H+) between reactants. Typically, an acid donates a proton to a base.

Each reaction follows an exchange of protons to form products:

• Acids are substances that can donate a proton (H+).
• Bases are substances that can accept a proton.

In the context of our exercise, when strontium oxide (a base in this case) reacts with water, it produces strontium hydroxide. This specific example is an oxide reacting with water, a particular type of acid-base reaction, highlighting how compounds form through hydroxide ions (OH-) instead of usual anions.

Combination Reactions

Combination reactions, also known as synthesis reactions, involve two or more reactants coming together to form a single product. These reactions can be simple or complex, yet they all follow the basic formula: A + B → AB.

Key properties to note:

• Reactants are generally elements or simple molecules.
• Products are typically more complex compounds.

For instance, when lithium reacts with oxygen, it forms lithium oxide, exemplifying a combination reaction. Similarly, sodium reacting with sulfur forms sodium sulfide. These reactions highlight how elements combine to form new, more complex substances.

Chemical Equations

Chemical equations are symbolic representations of a chemical reaction. They depict the substances involved in the reaction:

• The left side of the equation shows the reactants, the starting materials in a chemical reaction.
• The right side displays the products, substances formed as a result of the reaction.

The arrow symbol (→) indicates the direction of the reaction, from reactants to products.

Understanding how to write and interpret chemical equations is critical, as it allows scientists and students alike to visualize and comprehend the transformation of matter during reactions. Such knowledge aids in predicting the outcomes of reactions and understanding the principles governing them.