Complete And Balance The Equation For The Single-displacement Reaction.

Complete and Balance the Equation for a Single-Displacement Reaction: A Comprehensive Guide

Single-displacement reactions, also known as single replacement reactions, are a fundamental type of chemical reaction where one element replaces another element in a compound. Understanding how to complete and balance these equations is crucial for mastering stoichiometry and predicting the products of chemical reactions. This comprehensive guide will delve into the intricacies of single-displacement reactions, providing you with the tools and knowledge to confidently tackle any equation you encounter.

Understanding Single-Displacement Reactions

A single-displacement reaction follows a general pattern: A + BC → AC + B. Here, element A is more reactive than element B, allowing it to displace B from the compound BC. The reactivity of elements is typically determined by their position in the activity series (also known as the reactivity series), a list ranking elements based on their tendency to lose electrons and undergo oxidation. A more reactive element will readily displace a less reactive one.

The Activity Series: Your Key to Predicting Reactions

The activity series is a crucial tool for predicting whether a single-displacement reaction will occur. Elements higher on the series are more reactive and can displace elements lower on the list. For example, if you have zinc (Zn) and copper(II) sulfate (CuSO₄), you can consult the activity series. Since zinc is higher than copper, it will displace copper, resulting in the formation of zinc sulfate (ZnSO₄) and elemental copper (Cu).

A sample activity series (a more complete version can be found in your chemistry textbook):

• Most Reactive: Lithium (Li), Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminum (Al), Zinc (Zn), Iron (Fe), Lead (Pb), Hydrogen (H), Copper (Cu), Silver (Ag), Gold (Au) Least Reactive

Identifying Reactants and Products

Before you can balance the equation, you need to correctly identify the reactants and products. This involves understanding the chemical formulas of the involved elements and compounds. For example, in the reaction between zinc and hydrochloric acid, the reactants are zinc (Zn) and hydrochloric acid (HCl). Knowing that zinc is more reactive than hydrogen, we can predict that it will displace hydrogen, producing zinc chloride (ZnCl₂) and hydrogen gas (H₂).

Balancing Single-Displacement Reaction Equations

Balancing a chemical equation ensures that the number of atoms of each element is the same on both the reactant and product sides. This adheres to the law of conservation of mass, stating that matter cannot be created or destroyed in a chemical reaction. Here's a step-by-step approach to balancing single-displacement reactions:

Step 1: Write the Unbalanced Equation

Begin by writing the unbalanced equation using the correct chemical formulas for all reactants and products. For instance, the reaction between magnesium (Mg) and water (H₂O) would initially be written as:

Mg + H₂O → Mg(OH)₂ + H₂

Step 2: Identify the Elements to Balance

Identify the elements present on both sides of the equation and determine whether they are balanced. In our example, we see magnesium (Mg), oxygen (O), and hydrogen (H).

Step 3: Balance One Element at a Time

Start by balancing one element at a time. It's often easiest to begin with the element that appears in only one compound on each side of the equation. In this case, let's start with magnesium (Mg). It's already balanced (1 Mg atom on each side).

Step 4: Balance the Remaining Elements

Now, let's move on to oxygen and hydrogen. We have one oxygen on the left and two on the right. Let's add a coefficient of 2 in front of H₂O to balance oxygen:

Mg + 2H₂O → Mg(OH)₂ + H₂

Now, we have four hydrogen atoms on the left and four hydrogen atoms on the right. (2 from Mg(OH)2 and 2 from H2). Thus hydrogen is also balanced.

Step 5: Double Check the Balance

Finally, verify that the number of atoms of each element is equal on both sides. We have one magnesium, two oxygens, and four hydrogens on both sides. The equation is now balanced:

Mg + 2H₂O → Mg(OH)₂ + H₂

Examples of Single-Displacement Reactions and Balancing

Let's examine a few more examples to further solidify your understanding:

Example 1: Reaction between Iron and Copper(II) Sulfate

Iron (Fe) reacts with copper(II) sulfate (CuSO₄) to produce iron(II) sulfate (FeSO₄) and copper (Cu). The unbalanced equation is:

Fe + CuSO₄ → FeSO₄ + Cu

This equation is already balanced. Each element has the same number of atoms on both sides.

Example 2: Reaction between Chlorine and Sodium Bromide

Chlorine (Cl₂) reacts with sodium bromide (NaBr) to produce sodium chloride (NaCl) and bromine (Br₂). The unbalanced equation is:

Cl₂ + NaBr → NaCl + Br₂

To balance this equation:

1. Balance Chlorine: Add a coefficient of 2 in front of NaCl: Cl₂ + NaBr → 2NaCl + Br₂

2. Balance Bromine: Add a coefficient of 2 in front of NaBr: Cl₂ + 2NaBr → 2NaCl + Br₂

3. Double Check: The equation is now balanced with 2 chlorine, 2 sodium, and 2 bromine atoms on each side.

Example 3: A More Complex Example

Consider the reaction between aluminum (Al) and sulfuric acid (H₂SO₄):

Al + H₂SO₄ → Al₂(SO₄)₃ + H₂

Balancing this equation requires a multi-step approach:

1. Balance Aluminum: Add a coefficient of 2 in front of Al: 2Al + H₂SO₄ → Al₂(SO₄)₃ + H₂

2. Balance Sulfate (SO₄): Add a coefficient of 3 in front of H₂SO₄: 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + H₂

3. Balance Hydrogen: Add a coefficient of 3 in front of H₂: 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂

The equation is now balanced, with 2 aluminum, 6 hydrogen, 3 sulfur, and 12 oxygen atoms on each side.

Common Mistakes to Avoid

When balancing single-displacement reactions, several common mistakes can occur:

• Incorrect Formulas: Ensure you write the correct chemical formulas for all reactants and products. A single mistake here will throw off the entire balancing process.
• Forgetting to Balance All Elements: Carefully check that all elements are balanced on both sides of the equation.
• Changing Subscripts: Subscripts within a chemical formula indicate the number of atoms of an element in a molecule. These subscripts should never be changed when balancing an equation. Only coefficients (the numbers in front of the formulas) can be adjusted.
• Ignoring the Activity Series: Always consult the activity series to determine if a single-displacement reaction is even possible.

Conclusion: Mastering Single-Displacement Reactions

Completing and balancing single-displacement reaction equations is a fundamental skill in chemistry. By understanding the activity series, following the step-by-step balancing procedure, and avoiding common pitfalls, you can confidently predict products and balance these crucial chemical equations. This knowledge forms the basis for understanding more complex chemical reactions and stoichiometric calculations. Regular practice is key to mastering this skill, so work through numerous examples and test your understanding until you feel comfortable balancing any single-displacement reaction equation. Remember to always double-check your work to ensure accuracy!