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)

Verified step by step guidance

1. Identify the type of reactions: The first reaction involves the formation of ions where potassium loses an electron to form K+ and hydrogen gains an electron to form H-. The second reaction involves the opposite ion formation where potassium gains an electron to form K- and hydrogen loses an electron to form H+.
2. Use ionization energy and electron affinity data: For the first reaction, use the ionization energy of potassium (the energy required to remove an electron from K) and the electron affinity of hydrogen (the energy released when H gains an electron).
3. Calculate the energy change for the first reaction: Subtract the electron affinity of hydrogen from the ionization energy of potassium to find the net energy change for the formation of K+ and H-.
4. For the second reaction, use the electron affinity of potassium and the ionization energy of hydrogen: The electron affinity of potassium is the energy released when K gains an electron, and the ionization energy of hydrogen is the energy required to remove an electron from H.
5. Calculate the energy change for the second reaction: Subtract the ionization energy of hydrogen from the electron affinity of potassium to find the net energy change for the formation of K- and H+.
6. Compare the energy changes: Analyze which reaction is more favorable based on the calculated energy changes, considering that a negative energy change indicates a more favorable reaction.

Key Concepts

Ionic Compounds

Ionic compounds are formed through the transfer of electrons from one atom to another, resulting in the formation of charged ions. In the case of potassium hydride (KH), potassium (K) donates an electron to hydrogen (H), creating K+ and H- ions. Understanding the nature of ionic bonds is crucial for analyzing the energy changes during the formation and dissociation of such compounds.

Energy Change in Reactions

The energy change in a chemical reaction, often expressed in kJ/mol, indicates the difference in energy between reactants and products. This can be calculated using Hess's law or by analyzing bond energies. In the given reactions, determining the energy change involves understanding how the formation of ionic bonds releases energy, while breaking them requires energy input.

Standard State and Thermodynamic Data

Thermodynamic data, such as enthalpy changes, are typically reported under standard conditions (1 atm pressure and 25°C). Figures 7.10 and 7.12 likely provide necessary thermodynamic values for the reactants and products involved in the reactions. Familiarity with how to interpret and apply this data is essential for calculating the energy changes associated with the reactions of potassium and hydrogen.