8) Potassium and hydrogen react to form the ionic compound potassium hydride. (a

Question

8) Potassium and hydrogen react to form the ionic compound potassium hydride. (a) Write a balanced equation for this re- action. (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() K(g) H(g) K (g) H(g) (c) Based on your calculated energy changes in (b), which of these reactions is energetically more favorable (or less un- favorable)? (d) Is your answer to (c) consistent with the de- scription of potassium hydride as containing hydride ions?

Explanation / Answer

a) 2K(g) + H2(g) ---> 2KH(g)

Out of potassium and hydrogen,hydrogen is more electronegative and hence will have a more tendency to accept an electron as compared to Potassium.

b) K --> K+ I.E.= 419 kJ/mol

H ---> H- Electron affinity = -72.8 kJ/mol

Enthalpy change = 419 - 72.8 = 346.2 kJ/mol

K ---> K- Electron affinity = -48.4 kJ/mol

H ---> H+ Ionization energy = 1312 kJ/mol

Enthalpy change = 1312-48.4= 1263.6 kJ/mol

c) 1st reaction is less energy demanding as compared to 2nd reaction and thus,it is more favourable with respect to 2nd reaction

d) Yes. The answer is consistent with the formation of Potassium hydride containing hydride ions.

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