Problem 16 - Chemistry and Chemical Reactivity

Question

Write an equation for the reaction of potassium and hydrogen. Name the product. Is it ionic or covalent? Predict one physical property and one chemical property of this compound.

Step-by-Step Solution

Answer

Potassium hydride (KH) is ionic; it has a high melting point and reacts with water to release hydrogen gas.

Step 1: Identify Reactants

Potassium (K) is an alkali metal in Group 1 of the periodic table, and hydrogen (H) is a non-metal gas. When these two elements react, they form a compound. Potassium's electron configuration makes it eager to lose its one valence electron to achieve a stable octet.

Step 2: Write the Reaction Equation

Potassium reacts with hydrogen gas to form potassium hydride. The balanced chemical equation for this reaction is: \[2K(s) + H_2(g) ightarrow 2KH(s)\] This indicates that two atoms of potassium react with one molecule of hydrogen gas to produce two units of potassium hydride, a solid.

Step 3: Name the Product

The product formed from the reaction of potassium and hydrogen is potassium hydride (KH).

Step 4: Determine Chemical Bond Type

Potassium (a metal) and hydrogen (a non-metal) form an ionic bond. Potassium loses an electron to form a positively charged ion \( K^+ \), while hydrogen gains that electron to form a negatively charged hydride ion \( H^- \). This transfer of an electron characterizes an ionic bond.

Step 5: Predict Physical Property

As an ionic compound, potassium hydride is expected to have high melting and boiling points. It is typically found as a white crystalline solid at room temperature, a characteristic common among ionic compounds.

Step 6: Predict Chemical Property

One notable chemical property of potassium hydride is its reactivity with water. When KH is introduced to water, it reacts vigorously, releasing hydrogen gas: \[KH(s) + H_2O(l) ightarrow KOH(aq) + H_2(g)\] This reaction confirms KH's nature as a strong base.

Key Concepts

Ionic Compounds

Ionic compounds are formed when metals and non-metals react to create a strong bond. In these compounds, electrons are transferred from one atom to another. This transfer creates ions: atoms or molecules with an electrical charge.
For example, when a metal like potassium combines with a non-metal such as hydrogen, an ionic compound is created. Potassium loses an electron, becoming a positively charged ion \( K^+ \), while hydrogen gains an electron to form \( H^- \).
Some typical features of ionic compounds include:

• High melting and boiling points due to strong bonding.
• Generally solid and crystalline at room temperature.
• When dissolved in water, they conduct electricity.

These attributes make ionic compounds distinct and widely used in various applications.

Potassium Hydride

Potassium hydride \( KH \) is a specific ionic compound resulting from the reaction between potassium and hydrogen. It is a white crystalline solid typically formed when potassium metal combines with hydrogen gas.
This compound holds unique properties such as its high melting point, which is a result of the strong ionic bonds present. Additionally, potassium hydride is known for being highly reactive with water.
The reaction of \( KH \) with water is vigorous and releases hydrogen gas:
\[ KH(s) + H_2O(l) \rightarrow KOH(aq) + H_2(g) \]
This property is particularly significant because it highlights the compound's behavior as a potent base used in chemical reactions.

Chemical Bonding

Chemical bonding refers to the process by which atoms combine to form compounds. The type of bond formed greatly influences the resulting compound's properties.
In the case of ionic bonding, atoms transfer electrons to achieve a stable electronic configuration. Potassium, for instance, loses one electron, resulting in a \( K^+ \) ion. Hydrogen gains this electron, becoming \( H^- \).

• Such an electron transfer forms a strong electrostatic attraction between oppositely charged ions.
• This type of bond is known for creating solid structures with high lattice energy.

Understanding chemical bonding is essential for predicting how different substances will interact and combine, offering insights into their physical and chemical properties.

Chemical Properties

Chemical properties describe how substances interact with other materials and change their composition. For potassium hydride, reactivity with water is a defining chemical property.
When \( KH \) is exposed to water, it produces potassium hydroxide \( KOH \) and hydrogen gas \( H_2 \).
\[ KH(s) + H_2O(l) \rightarrow KOH(aq) + H_2(g) \]
This reaction is not only significant for producing hydrogen gas but also indicates \( KH \) as a caustic base.
Additional chemical properties of ionic compounds can include:

• Stability in their solid form.
• Ability to form new products when dissolved to make solutions.

These characteristics are crucial for various chemical processes and applications, including manufacturing and synthesis.