Question

(a) Write equations for the reactions of KH with \(\mathrm{NH}_{3}\) and with ethanol. (b) Identify the conjugate acid-base pairs in each reaction.

Short answer

KH reacts with NH₃ to form KNH₂ and H₂, and with ethanol to form C₂H₅OK and H₂. Conjugate pairs are KH/H₂ and NH₃/KNH₂ in the first reaction, and KH/H₂ and C₂H₅OH/C₂H₅O⁻ in the second.

Step-by-step solution

Write Equation for KH and NH3 Reaction

Potassium hydride (KH) reacts with ammonia (NH_3"). The reaction proceeds as follows: \(\mathrm{KH} + \mathrm{NH}_3 \rightarrow \mathrm{KNH}_2 + \mathrm{H}_2\).Here, hydrogen gas is released and potassium amide (KNH₂) is formed.

Identify Conjugate Acid-Base Pair in KH and NH3 Reaction

In the reaction \(\mathrm{KH} + \mathrm{NH}_3 \rightarrow \mathrm{KNH}_2 + \mathrm{H}_2\), the conjugate acid-base pairs are:1. Base: \(\mathrm{KH}\), which gives \(\mathrm{H}^-\) ion. Conjugate acid is \(\mathrm{H}_2\) after releasing \(\mathrm{H}^-\). 2. Acid: \(\mathrm{NH}_3\), which acts as a proton acceptor. Conjugate base is \(\mathrm{KNH}_2\) after donating a hydrogen ion.

Write Equation for KH and Ethanol Reaction

Potassium hydride reacts with ethanol (C₂H₅OH). The chemical equation is: \(\mathrm{KH} + \mathrm{C}_2\mathrm{H}_5\mathrm{OH} \rightarrow \mathrm{C}_2\mathrm{H}_5\mathrm{OK} + \mathrm{H}_2\).Hydrogen gas is again released, and potassium ethoxide (C₂H₅OK) is formed.

Identify Conjugate Acid-Base Pair in KH and Ethanol Reaction

In the reaction \(\mathrm{KH} + \mathrm{C}_2\mathrm{H}_5\mathrm{OH} \rightarrow \mathrm{C}_2\mathrm{H}_5\mathrm{OK} + \mathrm{H}_2\), the conjugate acid-base pairs are:1. Base: \(\mathrm{KH}\), providing \(\mathrm{H}^-\) ion, with \(\mathrm{H}_2 \) as the conjugate acid upon the release of \(\mathrm{H}^-\). 2. Acid: \(\mathrm{C}_2\mathrm{H}_5\mathrm{OH}\), which donates a proton to become \(\mathrm{C}_2\mathrm{H}_5\mathrm{O}^-\), the conjugate base.

Key concepts

Conjugate Acid-Base Pairs

In chemistry, a crucial aspect to understand in acid-base reactions is the concept of conjugate acid-base pairs. An acid-base pair includes an acid and a base that transform into each other by the gain or loss of a proton (H⁺ ion). Whenever an acid donates a proton, it becomes its conjugate base. Conversely, when a base accepts a proton, it becomes its conjugate acid.

• In the reaction between potassium hydride (KH) and ammonia (NH₃), KH functions as a base by releasing an H⁻ ion and ultimately forms molecular hydrogen (H₂) as its conjugate acid.
• Ammonia (NH₃) accepts a proton from KH, acting as an acid in this case, and transforms into potassium amide (KNH₂), which is the conjugate base.

Similarly, understanding conjugate acid-base pairs in the reaction between KH and ethanol (C₂H₅OH) offers clarity:

• KH once again acts as a base, forming molecular hydrogen (H₂) as its conjugate acid.
• Ethanol (C₂H₅OH) donates a proton, acting as an acid, and becomes potassium ethoxide (C₂H₅O⁻), the conjugate base.

Grasping these transformations allows for a deeper understanding of how acids and bases interact in chemical reactions.

Chemical Equations

Chemical equations represent the substances involved in a chemical reaction, showcasing the reactants transforming into products. Understanding the symbols and structure of these equations helps explain what is happening at the molecular level. For instance, in the reaction \[\mathrm{KH} + \mathrm{NH}_3 \rightarrow \mathrm{KNH}_2 + \mathrm{H}_2\]we see that potassium hydride (KH) and ammonia (NH₃) are the reactants. They react to form potassium amide (KNH₂) and hydrogen gas (H₂), which are the products.

• The reactants are placed on the left side of the equation, and the products are shown on the right side, separated by an arrow (→) indicating the direction of the reaction.
• In a balanced equation, the number of atoms of each element is conserved, meaning they appear equally on both sides.

This conservation shows that matter is neither created nor destroyed during a chemical reaction. By analyzing these equations, we gain an understanding of the quantities and-identities of the substances involved, allowing us to predict the outcome of reactions and their potential applications.

Reaction Mechanisms

Reaction mechanisms explain the step-by-step process through which a chemical reaction occurs. These mechanisms provide insight into the specific changes happening at the atomic or molecular level. The reactions between potassium hydride (KH) and either ammonia (NH₃) or ethanol (C₂H₅OH) illustrate clear steps:

• In both reactions, KH acts as a hydride donor, releasing a hydrogen ion, which is a key proton exchange process.
• Ammonia or ethanol, acting as acids, readily accept this proton, facilitating the formation of new products such as potassium amide or potassium ethoxide, respectively.

The energy changes and reactant interactions in these reactions are governed by the stability of intermediates and transition states. Understanding these steps helps predict how variations in conditions or reactants could affect the course of a reaction. By dissecting reaction mechanisms, chemists can manipulate conditions to optimize product yield, control reaction rates, and ensure safety in laboratory or industrial settings.