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 anyone studying chemistry, from high school students to advanced researchers. This comprehensive guide will walk you through the process, providing examples and tackling common challenges.

Understanding Single-Displacement Reactions

Before diving into balancing equations, let's solidify our understanding of the reaction itself. A single-displacement reaction follows a general pattern:

A + BC → AC + B

Where:

• A represents a more reactive element.
• B represents a less reactive element.
• BC represents a compound.
• AC represents a new compound formed.

The key is that element A displaces element B from the compound BC. This displacement only occurs if element A is more reactive than element B. Reactivity is often determined using the activity series of metals or the electronegativity series for non-metals.

The Activity Series of Metals

The activity series (also known as the reactivity series) is a list of metals ranked in order of their reactivity. Metals higher on the list are more reactive, meaning they are more likely to lose electrons and undergo oxidation. A metal higher on the series will displace a metal lower on the series from a compound. For example, zinc (Zn) is higher on the activity series than copper (Cu), so zinc will displace copper from copper(II) sulfate (CuSO₄).

Electronegativity and Non-Metals

While the activity series primarily applies to metals, a similar principle governs single-displacement reactions involving non-metals. Electronegativity, a measure of an atom's ability to attract electrons, plays a crucial role. A more electronegative non-metal will displace a less electronegative non-metal from a compound.

Steps to Complete and Balance Single-Displacement Equations

Completing and balancing a single-displacement equation involves two key steps:

1. Predicting the Products: Determine which element will displace the other based on the activity series or electronegativity.
2. Balancing the Equation: Ensure that the number of atoms of each element is the same on both the reactant and product sides.

Let's illustrate this with several examples.

Example 1: Reaction of Zinc with Hydrochloric Acid

Unbalanced equation: Zn + HCl → ?

Step 1: Predicting the Products

Zinc (Zn) is a more reactive metal than hydrogen (H), according to the activity series. Therefore, zinc will displace hydrogen from hydrochloric acid (HCl). The products will be zinc chloride (ZnCl₂) and hydrogen gas (H₂).

Step 2: Balancing the Equation

The predicted equation is: Zn + HCl → ZnCl₂ + H₂

Now, let's balance it:

• Zn: One Zn atom on each side (already balanced).
• Cl: Two Cl atoms on the product side, so we need two HCl molecules on the reactant side.
• H: Two H atoms on the product side (H₂), and now two H atoms on the reactant side (2HCl).

Balanced equation: Zn + 2HCl → ZnCl₂ + H₂

Example 2: Reaction of Bromine with Potassium Iodide

Unbalanced equation: Br₂ + KI → ?

Step 1: Predicting the Products

Bromine (Br) is more electronegative than iodine (I). Therefore, bromine will displace iodine from potassium iodide (KI). The products will be potassium bromide (KBr) and iodine (I₂).

Step 2: Balancing the Equation

The predicted equation is: Br₂ + KI → KBr + I₂

Now, let's balance it:

• K: One K atom on each side (already balanced).
• Br: Two Br atoms on the reactant side, so we need two KBr molecules on the product side.
• I: Two I atoms on the product side, so we need two KI molecules on the reactant side.

Balanced equation: Br₂ + 2KI → 2KBr + I₂

Example 3: A More Complex Example – Involving Polyatomic Ions

Unbalanced equation: Al + CuSO₄ → ?

Step 1: Predicting the Products

Aluminum (Al) is more reactive than copper (Cu). Aluminum will displace copper from copper(II) sulfate (CuSO₄). The products will be aluminum sulfate (Al₂(SO₄)₃) and copper (Cu).

Step 2: Balancing the Equation

The predicted equation is: Al + CuSO₄ → Al₂(SO₄)₃ + Cu

Balancing this equation requires careful attention to the polyatomic ion (SO₄²⁻):

• Al: Two Al atoms on the product side, so we need two Al atoms on the reactant side.
• SO₄²⁻: Three SO₄²⁻ ions on the product side, so we need three CuSO₄ molecules on the reactant side.
• Cu: Three Cu atoms on the product side, so we need three Cu atoms on the product side.

Balanced equation: 2Al + 3CuSO₄ → Al₂(SO₄)₃ + 3Cu

Common Challenges and Troubleshooting

Balancing single-displacement reactions can sometimes present challenges. Here are some common issues and how to address them:

• Incorrect Product Prediction: Carefully consult the activity series or electronegativity values to ensure you accurately predict the products. An incorrect prediction will lead to an impossible-to-balance equation.
• Ignoring Polyatomic Ions: Treat polyatomic ions as single units when balancing. Don't break them apart into individual atoms.
• Fractional Coefficients: While it's sometimes necessary to use fractional coefficients as an intermediate step, the final balanced equation should have only whole number coefficients. Multiply the entire equation by the denominator to eliminate fractions.

Advanced Applications and Considerations

Understanding single-displacement reactions extends beyond simple textbook examples. They are crucial in various applications, including:

• Metallurgy: Extracting metals from their ores often involves single-displacement reactions.
• Electrochemistry: These reactions form the basis of many electrochemical cells and batteries.
• Industrial Processes: Many industrial processes utilize single-displacement reactions for synthesis and purification.

Conclusion

Mastering the art of completing and balancing single-displacement reaction equations is an essential skill in chemistry. By understanding the underlying principles of reactivity, carefully predicting products, and systematically balancing the equation, you can confidently tackle even the most complex examples. Remember to consult the activity series or electronegativity values, treat polyatomic ions as units, and check your work to ensure the number of atoms of each element is the same on both sides of the equation. With practice, you will develop the proficiency to confidently and accurately balance these important chemical reactions.