Question

Complete and balance each of the following single-replacement reactions: (a) \(\mathrm{K}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow\) (b) \(\mathrm{Ba}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow\)

Short answer

(a) \( 2\mathrm{K}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2\mathrm{KOH}(aq) + \mathrm{H}_{2}(g) \); (b) \( \mathrm{Ba}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{Ba(OH)}_2(aq) + \mathrm{H}_{2}(g) \).

Step-by-step solution

Identify the Type of Reaction

Both reactions are single-replacement reactions where a reactive metal displaces hydrogen from water. The general form is: \( \text{Metal} + \text{Water} \rightarrow \text{Metal Hydroxide} + \text{Hydrogen Gas} \).

Write the Products for the Reaction (a)

For the reaction of potassium with water: \( \mathrm{K}(s) + \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{KOH}(aq) + \mathrm{H}_{2}(g) \). Potassium displaces hydrogen to form potassium hydroxide and hydrogen gas.

Balance the Reaction (a)

Balance the chemical equation: \[ 2\mathrm{K}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2\mathrm{KOH}(aq) + \mathrm{H}_{2}(g) \]. Ensure there are equal numbers of each type of atom on both sides.

Write the Products for the Reaction (b)

For the reaction of barium with water: \( \mathrm{Ba}(s) + \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{Ba(OH)}_2(aq) + \mathrm{H}_{2}(g) \). Barium reacts with water to form barium hydroxide and hydrogen gas.

Balance the Reaction (b)

Balance the chemical equation: \[ \mathrm{Ba}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{Ba(OH)}_{2}(aq) + \mathrm{H}_{2}(g) \]. Make sure the number of atoms for each element is equal on both sides.

Key concepts

Single-Replacement Reactions

Single-replacement reactions, also known as substitution reactions, are intriguing and often simple to understand. These reactions occur when an element reacts with a compound and takes the place of another element within that compound. The general formula for this type of reaction is:

• A + BC → AC + B

In the given exercise, both reactions are examples of a metal (such as potassium or barium) reacting with water. Here, the metal displaces hydrogen in water, ultimately producing a metal hydroxide and hydrogen gas. This can be illustrated with the example of potassium:

• Potassium plus water yields potassium hydroxide and hydrogen gas: \( \mathrm{2K}(s) + 2\mathrm{H}_{2}\mathrm{O}(l) \rightarrow 2\mathrm{KOH}(aq) + \mathrm{H}_{2}(g) \).

Understanding the typical patterns of single-replacement reactions helps predict the products formed. These reactions can be spotted by noting how one element dislodges another, swapping places and resulting in a new compound and a release of another element.

Reactants and Products

Reactants and products are fundamental components of any chemical reaction, seamlessly reflecting transformation. In any chemical reaction, reactants are the starting materials that undergo a chemical change. In contrast, products are the new substances formed as a result of the reaction.

• **Reactants** in the problem are potassium \((\mathrm{K})\) and water \((\mathrm{H}_{2} \mathrm{O})\) in reaction \(a\) along with barium \((\mathrm{Ba})\) and water in reaction \(b\).
• **Products** include potassium hydroxide \((\mathrm{KOH})\) and hydrogen gas \((\mathrm{H}_{2})\) for reaction \(a\), and barium hydroxide \((\mathrm{Ba(OH)}_2)\) and hydrogen gas for reaction \(b\).

Recognizing reactants and products helps understand the chemical reaction, aiding in prediction and balancing of the equation. For each reaction, noting what substances start and what they become is key. This guides in accurately placing formulas and balancing reactions as per the law of conservation of mass. Products are identified and written on the right side of the reaction arrow, while reactants are listed on the left.

Conservation of Mass in Chemical Reactions

The principle of conservation of mass is crucial in chemistry, dictating that mass is neither created nor destroyed in a chemical reaction. This principle ensures that the mass of reactants in a chemical equation must equal the mass of the products. Therefore, balancing chemical equations is indispensable to maintain this principle.

• To balance any reaction, ensure the number of atoms for each element on the reactant side equals those on the product side.
• Take, for example, the balanced equation for the reaction of potassium and water: \[2\mathrm{K}(s) + 2\mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2\mathrm{KOH}(aq) + \mathrm{H}_{2}(g)\].
• Here, there are two potassium atoms, four hydrogen atoms, and two oxygen atoms on both sides of the equation.

Balancing requires changing coefficients, not altering the chemical formulas of reactants or products. Conservation of mass ensures all atoms present in the reactants are accounted for in the products, leading to an unwavering constancy that ascertains accuracy in chemical reactions and equations.