Question

a. Give two examples each of a single-displacement reaction and of a double- replacement reaction. How are the two reaction types similar, and how are they different? b. Give two examples each of a reaction in which formation of water is the driving force and in which formation of a gas is the driving force.

Short answer

Two examples of single-displacement reactions are: 1. Zn + 2HCl → ZnCl2 + H2 2. Fe + CuSO4 → FeSO4 + Cu Two examples of double-replacement reactions are: 1. NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s) 2. CaCl2(aq) + 2KOH(aq) → Ca(OH)2(s) + 2KCl(aq) The two reaction types are similar in the sense that they involve atoms or ions swapping places in the reactants. However, in single-displacement reactions, only one element replaces another, while in double-replacement reactions, two cations swap places between the compounds. Two examples of reactions driven by the formation of water are: 1. HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq) 2. H2SO4(aq) + 2KOH(aq) → 2H2O(l) + K2SO4(aq) Two examples of reactions driven by the formation of a gas are: 1. CaCO3(s) → CaO(s) + CO2(g) 2. NaHCO3(s) + CH3COOH(aq) → CO2(g) + H2O(l) + NaCH3COO(aq)

Step-by-step solution

Understanding Single-Displacement Reaction

In a single-displacement reaction, an element from one reactant replaces another element in another reactant, creating a new product. This occurs when a more reactive element displaces a less reactive one. The general form of a single-displacement reaction is AB + C → AC + B, where element C replaces element B in the compound AB.

Examples of Single-Displacement Reactions

Example 1: A reaction between zinc and hydrochloric acid: Zn + 2HCl → ZnCl2 + H2 Here, the zinc (Zn) displaces the hydrogen ions (H) in the hydrochloric acid (HCl) to produce zinc chloride (ZnCl2) and hydrogen gas (H2). Example 2: A reaction between copper sulfate and iron: Fe + CuSO4 → FeSO4 + Cu In this example, iron (Fe) displaces copper (Cu) in the compound copper sulfate (CuSO4) to produce iron sulfate (FeSO4) and copper.

Understanding Double-Replacement Reaction

In a double-replacement reaction, two ionic compounds (often in aqueous solution) swap partners with each other, resulting in two new compounds. The general form of a double-replacement reaction is AB + CD → AD + CB, where the cations (A and C) switch places with each other in the compounds.

Examples of Double-Replacement Reactions

Example 1: A reaction between sodium chloride and silver nitrate: NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s) Here, the sodium (Na) and silver (Ag) ions swap places, resulting in the formation of sodium nitrate (NaNO3) and solid silver chloride (AgCl). Example 2: A reaction between calcium chloride and potassium hydroxide: CaCl2(aq) + 2KOH(aq) → Ca(OH)2(s) + 2KCl(aq) In this reaction, calcium (Ca) and potassium (K) ions swap places, forming calcium hydroxide (Ca(OH)2) and potassium chloride (KCl).

Water Formation as a Driving Force and Examples

Reactions in which the formation of water serves as the driving force are called acid-base neutralization reactions. In these reactions, an acid reacts with a base to form water and a salt. Example 1: A reaction between hydrochloric acid and sodium hydroxide: HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq) The acid (HCl) reacts with the base (NaOH) to form water (H2O) and sodium chloride (NaCl) as a salt. Example 2: A reaction between sulfuric acid and potassium hydroxide: H2SO4(aq) + 2KOH(aq) → 2H2O(l) + K2SO4(aq) Here, sulfuric acid (H2SO4) reacts with potassium hydroxide (KOH) to form water (H2O) and potassium sulfate (K2SO4).

Gas Formation as a Driving Force and Examples

Reactions in which the formation of a gas serves as the driving force are often decomposition reactions or reactions involving the release of a certain gas as a product. Example 1: Thermal decomposition of calcium carbonate: CaCO3(s) → CaO(s) + CO2(g) When calcium carbonate (CaCO3) is heated, it decomposes to form calcium oxide (CaO) and carbon dioxide (CO2) gas. Example 2: Reaction between baking soda and vinegar: NaHCO3(s) + CH3COOH(aq) → CO2(g) + H2O(l) + NaCH3COO(aq) The reaction between baking soda (sodium bicarbonate, NaHCO3) and vinegar (acetic acid, CH3COOH) results in the production of carbon dioxide (CO2) gas, water (H2O), and sodium acetate (NaCH3COO).

Key concepts

Single-Displacement Reaction

Imagine being at a dance where you're partnered with another dancer. A single-displacement reaction is somewhat like a dance where a third person steps in, and you find yourself without a partner. In a chemical context, this type of reaction involves an element 'dancing' away from its compound to 'partner up' with another element. More technically, it's a reaction where one element replaces another in a compound, forming a new substance.

For instance, consider a piece of zinc metal reacting with hydrochloric acid. The zinc 'cuts in' and takes the place of the hydrogen in the acid, producing zinc chloride and hydrogen gas. This kind of exchange can only happen if the incoming solo element is more reactive than the one it's looking to replace.

• Zn + 2HCl → ZnCl₂ + H₂
• Fe + CuSO₄ → FeSO₄ + Cu

These examples show how a single-displacement reaction can easily be spotted by its characteristic format of AB + C going to AC + B. It's essential for students to recognize how this pattern is distinct from other types of reactions.

Double-Replacement Reaction

Now, imagine that dance again, but this time, each couple swaps partners. Suddenly, you have a double-replacement reaction on the dance floor! It's the chemical equivalent of a partner swap: two ionic compounds exchange their cations or anions to create two new compounds.

Here's how it looks when sodium chloride meets silver nitrate in a solution. They perform a partner-swapping number, which ends up with sodium pairing with nitrate and silver linking up with chloride to form a precipitate. And like any good dance partner, these elements need to be compatible, or soluble, to 'dance' together in solution.

• NaCl(aq) + AgNO₃(aq) → NaNO₃(aq) + AgCl(s)
• CaCl₂(aq) + 2KOH(aq) → Ca(OH)₂(s) + 2KCl(aq)

Recognizing the AB + CD going to AD + CB pattern is critical for identifying these reactions. It's a classic dance of the elements and one that's pivotal in the study of chemistry.

Acid-Base Neutralization

When an acid and a base get together, they tend to cancel each other out in what's known as an acid-base neutralization reaction. It's like merging a hot desert wind with a cool ocean breeze to get a comfortable temperature. In chemistry, this is a reaction where the acid's 'hot' H+ ions combine with the base's 'cool' OH- ions to form water, which can feel a bit like chemical harmony.

Along with water, this reaction also creates salt, which is a compound consisting of the remaining ions from the acid and base. Two classic examples demonstrate this effect quite well:

• HCl(aq) + NaOH(aq) → H₂O(l) + NaCl(aq)
• H₂SO₄(aq) + 2KOH(aq) → 2H₂O(l) + K₂SO₄(aq)

Through these reactions, students can observe how the acidity and basicity neutralize each other and provide an intuitive understanding of pH balance in chemical solutions.

Gas Formation in Reactions

When you think of chemistry, bubbling test tubes might come to mind. Often, those bubbles are the result of gas forming during a reaction. The production of a gas can serve as a powerful driving force behind chemical changes.

For example, when baking soda meets vinegar, the reaction produces carbon dioxide, the same gas that adds fizz to sodas. This kind of reaction is not only visually spectacular but also provides evidence of a chemical change. The release of gas can be an indication of a reaction taking place, it can help in propelling rockets, or even make a simple volcano science project come to life.

• CaCO₃(s) → CaO(s) + CO₂(g)
• NaHCO₃(s) + CH₃COOH(aq) → CO₂(g) + H₂O(l) + NaCH₃COO(aq)

Understanding how and why these gas-producing reactions occur can help students predict the outcomes of chemical experiments and appreciate the energy changes involved in chemical processes.