Problem 22 - 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

The reaction is \( 2K + H_2 \rightarrow 2KH \). The product is potassium hydride, which is ionic. It is a white solid with high melting point and reacts vigorously with water.

Step 1: Identify Reactants

First, identify the elements involved in the reaction. In this case, the reactants are potassium (K) and hydrogen (H).

Step 2: Write the Chemical Equation

Potassium reacts with hydrogen to form potassium hydride. This reaction can be represented by the chemical equation: \( 2K + H_2 ightarrow 2KH \).

Step 3: Name the Product

The product of the reaction between potassium and hydrogen is potassium hydride, denoted by the chemical formula \( KH \).

Step 4: Determine Bond Type

Potassium hydride (KH) consists of potassium, a metal, and hydrogen, a non-metal. The bond is ionic because potassium donates an electron to hydrogen, forming a positive potassium ion \( K^+ \) and a hydride ion \( H^- \).

Step 5: Predict Physical Property

Potassium hydride is a white crystalline solid at room temperature. It is ionic and thus has a high melting point, typical for ionic compounds.

Step 6: Predict Chemical Property

Chemically, potassium hydride is highly reactive, especially with water. When it comes into contact with water, it reacts vigorously, producing hydrogen gas and potassium hydroxide: \( KH + H_2O ightarrow KOH + H_2 \).

Key Concepts

Ionic Compounds

Ionic compounds are an essential type of chemical compound characterized by their unique bonding and properties. They are formed when atoms transfer electrons between each other. This electron exchange results in the creation of ions. In ionic compounds, one atom becomes positively charged (cation), while the other becomes negatively charged (anion).

• Ionic bonds typically occur between metals, which lose electrons, and non-metals, which gain them.
• The electrostatic attraction between oppositely charged ions holds the compound together.

Ionic compounds usually form crystalline structures at room temperature. They have high melting and boiling points due to the strong attraction between the ions. They are often soluble in water and can conduct electricity when dissolved or melted, as the free-moving ions act as charge carriers. An example of an ionic compound is potassium hydride (KH), formed from potassium and hydrogen.

Chemical Equation

A chemical equation is a symbolic representation of a chemical reaction. It showcases the reactants transforming into the products, illustrating both the substances involved and the quantities in which they react and form. In the case of the reaction between potassium and hydrogen, the chemical equation is:\[2K + H_2 \rightarrow 2KH\]

• The left side shows the reactants: two potassium atoms and one hydrogen molecule.
• The arrow signifies the reaction process, leading to the formation of products on the right side.
• The right side lists two units of potassium hydride, the resulting product.

Chemical equations must be balanced, meaning the number of atoms for each element must be equal on both sides of the equation. This balance is crucial because it respects the law of conservation of mass, ensuring no atoms are lost or gained in the reaction process.

Potassium Hydride

Potassium hydride, with the chemical formula \( KH \), is an example of an ionic compound, resulting from the reaction between potassium (K) and hydrogen (H). This compound is formed when potassium, a highly reactive alkali metal, donates its outermost electron to hydrogen, forming ionic bonds. The resulting ions are potassium cations \( K^+ \) and hydride anions \( H^- \).Potassium hydride appears as a white crystalline solid at room temperature. Some notable properties of potassium hydride include:

• High melting point, a typical characteristic of ionic compounds due to their strong ionic bonds.
• Reactivity with water, making it a versatile reagent in various industrial and laboratory applications.

Potassium hydride is highly reactive and should be handled with care. It is stored under inert conditions to prevent any accidental contact with moisture or air.

Reactivity with Water

Reactivity with water is an important characteristic of many chemical compounds, indicating how they react when coming into contact with water. Potassium hydride is highly reactive when exposed to water. This reactivity stems from its ionic nature and the tendencies of its constituent elements.When potassium hydride (\( KH \)) encounters water (\( H_2O \)), a vigorous reaction occurs:\[ KH + H_2O \rightarrow KOH + H_2 \]

• Potassium hydride reacts to form potassium hydroxide \( KOH \), a strong base that dissolves in water.
• Hydrogen gas \( H_2 \) is released as a byproduct, which can be very flammable and should be handled with caution.

This reaction requires careful handling due to the rapid formation of flammable hydrogen gas and the caustic nature of the resulting potassium hydroxide. Such reactivity highlights the importance of understanding chemical properties in predicting and managing reactions safely in both industrial processes and laboratory environments.