Potassium and hydrogen react to form the ionic compound...

Potassium and hydrogen react to form the ionic compound potassium hydride. (a) Write a balanced equation for this reaction. (b) Use data in Figures 7.10 and 7.12 to determine the energy change in $\mathrm{kJ} / \mathrm{mol}$ for the following two reactions: $$ \begin{aligned} & \mathrm{K}(g)+\mathrm{H}(g) \longrightarrow \mathrm{K}^{+}(g)+\mathrm{H}^{-}(g) \\ & \mathrm{K}(g)+\mathrm{H}(g) \longrightarrow \mathrm{K}^{-}(g)+\mathrm{H}^{+}(g) \end{aligned} $$ (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?

Potassium and hydrogen react to form the ionic compound potassium hydride. (a) Write a balanced equation for this reaction. (b) Use data in Figures 7.10 and 7.12 to determine the energy change in $\mathrm{kJ} / \mathrm{mol}$ for the following two reactions:
$$
\begin{aligned}
& \mathrm{K}(g)+\mathrm{H}(g) \longrightarrow \mathrm{K}^{+}(g)+\mathrm{H}^{-}(g) \\
& \mathrm{K}(g)+\mathrm{H}(g) \longrightarrow \mathrm{K}^{-}(g)+\mathrm{H}^{+}(g)
\end{aligned}
$$
(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?

Key Concepts

Balanced Chemical Equations

A balanced chemical equation provides a symbolic representation of a chemical reaction with the correct relative proportions of reactants and products. This ensures that the law of conservation of mass is fulfilled, meaning the number of atoms for each element is the same on both sides of the equation.

Ionic Bonding

Ionic bonding is the electrostatic attraction between oppositely charged ions, typically formed when one atom donates an electron to another. The resulting ionic compounds, such as those containing a metal cation and a nonmetal anion, have crystal lattice structures that provide distinctive physical properties like high melting points.

Ionization Energy

Ionization energy is the amount of energy required to remove an electron from a gaseous atom or ion, forming a positive ion. It is a critical factor when considering the formation of cations in ionic reactions, as it represents an energy cost that must be overcome.

Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a gaseous atom, forming a negative ion. This value indicates how strongly an atom attracts additional electrons and influences the energetics of forming anions in ionic processes.

Reaction Energetics

Reaction energetics involves calculating the overall energy changes during a chemical reaction by considering the energy required for electron removal and the energy released upon electron addition. These calculations help determine whether a reaction is endothermic or exothermic, influencing its spontaneity.

Thermodynamic Favorability

Thermodynamic favorability refers to the relative stability of reaction pathways based on energy changes. When comparing alternative reactions, the pathway requiring less net energy input or releasing more energy is considered more favorable, linking molecular energetics with reaction feasibility.

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