Problem 43 - Chemistry and Chemical Reactivity

Question

Write an overall, balanced equation for the reaction of \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{S}\) with \(\mathrm{HBr}\), and name the reactants and products.

Step-by-Step Solution

Answer

The balanced equation is \( (NH_4)_2S + 2HBr \rightarrow 2NH_4Br + H_2S \). Reactants: ammonium sulfide, hydrobromic acid. Products: ammonium bromide, hydrogen sulfide.

Step 1: Identify Reactants

The given reactants are ammonium sulfide \((NH_4)_2S\) and hydrobromic acid \(HBr\). We need to determine the products these reactants will form.

Step 2: Predict Products

Ammonium sulfide will react with hydrobromic acid to form ammonium bromide \(NH_4Br\) and hydrogen sulfide \(H_2S\). This is a double displacement reaction where ions exchange partners.

Step 3: Write Unbalanced Equation

The unbalanced chemical equation based on the predicted reactants and products is: \( (NH_4)_2S + HBr \rightarrow NH_4Br + H_2S \).

Step 4: Balance Equation

Balancing the equation involves ensuring the same number of each type of atom on both sides of the equation. The balanced equation is:\[ (NH_4)_2S + 2HBr \rightarrow 2NH_4Br + H_2S \]Each side now has 2 nitrogen, 8 hydrogen, 1 sulfur, and 2 bromine atoms.

Step 5: Name Reactants and Products

The reactants are ammonium sulfide and hydrobromic acid. The products are ammonium bromide and hydrogen sulfide.

Key Concepts

Understanding Double Displacement Reactions

In the world of chemistry, a double displacement reaction is one where the ions in two compounds exchange partners. Imagine it like swapping dance partners, where each partner finds a new match. This type of reaction often occurs in aqueous solutions and can result in the formation of a precipitate, a gas, or water.

In our exercise, ammonium sulfide \((NH_4)_2S\) reacts with hydrobromic acid \(HBr\). The ammonium \(NH_4^+\) ions pair with bromide \(Br^-\) ions, forming ammonium bromide \(NH_4Br\). Meanwhile, sulfide \(S^{2-}\) ions pair with hydrogen \(H^+\), creating hydrogen sulfide \(H_2S\).

• Ammonium \(NH_4^+\) swaps its partner from sulfide \(S^{2-}\) to bromide \(Br^-\).
• Sulfide \(S^{2-}\) finds hydrogen \(H^+\) as its new partner.

These partner swaps perfectly demonstrate the nature of double displacement reactions.

Balancing Chemical Equations

Balancing a chemical equation means making sure that the same number of each type of atom appears on both sides of the equation. This keeps the law of conservation of mass intact, indicating that matter is neither created nor destroyed.

For our reaction, we start with the unbalanced equation: \( (NH_4)_2S + HBr \rightarrow NH_4Br + H_2S \).

To balance this equation, we first count each atom in the reactants and products:

• 2 nitrogen atoms
• 8 hydrogen atoms
• 1 sulfur atom
• 2 bromine atoms

Based on the counts, the balanced equation becomes: \[ (NH_4)_2S + 2HBr \rightarrow 2NH_4Br + H_2S \]
This ensures that each side accurately reflects the same quantity of each element. Balancing equations is crucial in ensuring chemical reactions are accurately described.

Naming Chemical Compounds

Understanding how to name chemical compounds is essential for communicating in chemistry. Compounds are typically named based on the ions they contain.

In our example:

• Ammonium sulfide \((NH_4)_2S\) consists of ammonium ions \(NH_4^+\) and sulfide ions \(S^{2-}\).
• Hydrobromic acid \(HBr\) is named because it contains hydrogen ions \(H^+\) combined with bromide ions \(Br^-\).
• Ammonium bromide \(NH_4Br\) is the result of ammonium ions combining with bromide ions.
• Hydrogen sulfide \(H_2S\) is formed when hydrogen ions pair with sulfide ions.

Naming helps identify the composition and potential reactions of the compounds, making this skill critical for anyone studying chemistry. Understanding these names allows chemists to predict and describe reactions accurately.