Question

Consider the reaction classifications we studied in Chapter 5. For each reaction type given, write a chemical reaction in which \(\mathrm{HCl}\) is a reactant. (a) neutralization (double-displacement) (b) single-displacement

Short answer

The neutralization reaction of HCl with NaOH is: \(\mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{H_2O} + \mathrm{NaCl}\). The single-displacement reaction of HCl with K is: \(\mathrm{K} + \mathrm{HCl} \rightarrow \mathrm{KCl} + \mathrm{H_2}\).

Step-by-step solution

Writing the Neutralization Reaction

To write a neutralization reaction, we need an acid and a base. Here, we are given Hydrochloric acid (HCl) as a reactant, which is an acid. We can consider Sodium hydroxide (NaOH) as a base. So, when Hydrochloric acid reacts with Sodium hydroxide, it results in the formation of water (H2O) and Sodium chloride (NaCl), a salt. So, the chemical reaction becomes: \[ \mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{H_2O} + \mathrm{NaCl} \]

Writing the Single-Displacement Reaction

In a single displacement reaction, a more reactive element displaces a less reactive element from its compound. Here, with Hydrochloric acid (HCl) as a reactant, we can consider Potassium (K), a metal more reactive than Hydrogen from the reactivity series. When Potassium reacts with Hydrochloric acid, it displaces Hydrogen from the HCl compound, resulting in the formation of Potassium Chloride (KCl) and Hydrogen gas (H2). So, the chemical reaction becomes: \[ \mathrm{K} + \mathrm{HCl} \rightarrow \mathrm{KCl} + \mathrm{H_2} \]

Key concepts

Neutralization Reaction

Neutralization reactions are an essential topic in chemistry, especially when studying how acids and bases interact. A neutralization reaction typically involves an acid and a base combining to form water and a salt. This type of reaction falls under double-displacement reactions, where the ions of the reactants exchange places. In the example provided, Hydrochloric acid (HCl) and Sodium hydroxide (NaOH) are the starting reactants. Hydrochloric acid is a strong acid, while Sodium hydroxide is a strong base. These two substances react to form water (\( \mathrm{H_2O} \)) and Sodium chloride (\( \mathrm{NaCl} \)).

• The hydrogen ion (\( \mathrm{H^+} \)) from HCl combines with the hydroxide ion (\( \mathrm{OH^-} \)) from NaOH to form water.
• The sodium ion (\( \mathrm{Na^+} \)) pairs with the chloride ion (\( \mathrm{Cl^-} \)) to produce the salt, NaCl.

Through this process, neutralization reactions often lead to the solution becoming neutral, with a pH of around 7. This is an ideal situation since neither acidic nor basic conditions prevail.

Single-Displacement Reaction

Single-displacement reactions, also known as single-replacement reactions, involve one element being substituted by another in a compound. This occurs based on the reactivity series, which ranks elements by their ability to displace others. More reactive elements can replace less reactive ones. In the example involving Hydrochloric acid (\( \mathrm{HCl} \)) and Potassium (K), Potassium acts as a more reactive element than Hydrogen. As a result, Potassium displaces Hydrogen in Hydrochloric acid, forming Potassium chloride (\( \mathrm{KCl} \)) and Hydrogen gas (\( \mathrm{H_2} \)).

• Potassium donates electrons to two Chlorine atoms, forming two units of Potassium chloride.
• Hydrogen receives the electrons and forms Hydrogen gas, observable in the reaction as bubbles.

These reactions are common in metals reacting with acids, where the product can involve elemental hydrogen, which is a diatomic molecule in its natural state.

Reaction Types

Understanding the different types of chemical reactions is fundamental in chemistry. Each type of reaction follows its unique pattern based on the nature of the materials involved and the changes they undergo. The major types of reactions include

• **Combination reactions**, where two or more substances combine to form a single product.
• **Decomposition reactions**, which involve a single compound breaking down into two or more simpler products.
• **Single-displacement reactions**, as discussed, involve an element displacing another from a compound.
• **Double-displacement reactions**, or exchange reactions, involve exchanging ions between two compounds, such as in neutralization reactions.
• **Combustion reactions**, where a material reacts with oxygen, releasing energy, and often producing flame.

Studying these types helps us to predict the products of chemical reactions and understand the processes that take place in reactions. Knowing the reaction type also aids in balancing chemical equations, which ensures that mass and charge are conserved during the process.