Potassium and hydrogen react to form the ionic compound potassium hydride. (c) Based on your calculated energy changes in (b), which of these reactions is energetically more favorable (or less unfavorable)? (d) Is your answer to (c) consistent with the description of potassium hydride as containing hydride ions?

Verified step by step guidance

To determine which reaction is energetically more favorable, compare the calculated energy changes from part (b) for the formation of potassium hydride. The reaction with the lower energy change (more negative) is more favorable.

Recall that the formation of an ionic compound involves the transfer of electrons. Potassium (K) loses one electron to form K⁺, and hydrogen (H) gains one electron to form H^- (hydride ion).

Consider the lattice energy of potassium hydride, which is the energy released when gaseous ions combine to form the ionic solid. A more negative lattice energy indicates a more stable ionic compound.

Check if the calculated energy changes align with the concept of hydride ions. Hydride ions (H^-) are known for their high electron affinity, which should be reflected in the energy calculations.

Evaluate if the description of potassium hydride as containing hydride ions is consistent with the energy favorability. If the reaction forming hydride ions is more favorable, it supports the description.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ionic Bonding

Ionic bonding occurs when atoms transfer electrons, resulting in the formation of charged ions. In the case of potassium hydride, potassium (K) donates an electron to hydrogen (H), creating K+ and H- ions. The electrostatic attraction between these oppositely charged ions leads to the formation of the ionic compound, which is characterized by high melting points and electrical conductivity in molten or dissolved states.

Energetics of Reactions

The energetics of a reaction refers to the changes in energy that occur during the reaction process. This includes the energy required to break bonds in the reactants and the energy released when new bonds form in the products. A reaction is considered energetically favorable if it results in a net release of energy, often indicated by a negative change in Gibbs free energy, which drives the reaction towards completion.

Hydride Ions

Hydride ions (H-) are formed when hydrogen gains an electron, resulting in a negatively charged ion. In potassium hydride, the presence of hydride ions indicates that hydrogen is acting as a reducing agent, allowing it to bond with potassium. The stability and properties of ionic compounds like potassium hydride are influenced by the presence of these hydride ions, which contribute to the overall lattice energy and stability of the compound.

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Ionic Hydrides

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(a) As described in Section 7.7, the alkali metals react with hydrogen to form hydrides and react with halogens to form halides. Compare the roles of hydrogen and halogens in these reactions. Write balanced equations for the reaction of fluorine with calcium and for the reaction of hydrogen with calcium. (b) What is the oxidation number and electron configuration of calcium in each product?

Textbook Question

Potassium and hydrogen react to form the ionic compound potassium hydride. (b) Use data in Figures 7.10 and 7.12 to determine the energy change in kJ/mol for the following two reactions:

K(g) + H(g) → K⁺(g) + H^-(g)

K(g) + H(g) → K^-(g) + H⁺(g)

Textbook Question

Little is known about the properties of astatine, At, because of its rarity and high radioactivity. Nevertheless, it is possible for us to make many predictions about its properties. (a) Do you expect the element to be a gas, liquid, or solid at room temperature?