   Chapter 12, Problem 12.134QP General Chemistry - Standalone boo...

11th Edition
Steven D. Gammon + 7 others
ISBN: 9781305580343

Solutions

Chapter
Section General Chemistry - Standalone boo...

11th Edition
Steven D. Gammon + 7 others
ISBN: 9781305580343
Textbook Problem

The lattice enthalpy of potassium chloride is 717 kJ/mol; the heat of solution in making up l M KCl(aq) is +18.0 kJ/mol. Using the value for the heat of hydration of Cl− given in Problem 12.133, obtain the heat of hydration of K+. Compare this with the value you obtained for Na+ in Problem 12.133. Explain the relative values of Na+ and K +.

Interpretation Introduction

Interpretation:

Heat of hydration of K+ ion has to be calculated and compared with that of Na+ .

Concept Introduction:

• The energy released when gaseous state ions of unlike charges that are infinitely farther apart combine to form a stable ionic solid is called Lattice energy.  Conversely, the energy required to break the electrostatic force of attraction between the ions of unlike charges in the ionic solid and revert them to gaseous state is also termed as Lattice energy of an ionic solid.
• Hydration energy refers to the quantity of energy released when one mole of ion gets hydrated at constant pressure.  Hydration energy of an ion depends upon its ionic size.
Explanation

Given that lattice enthalpy of potassium chloride is 717 kJ/mol. heat of solution of aqueous NaCl is +18 kJ/mol.   lattice enthalpy is energy released when one mole of KCl is formed. Therefore, Sum of heat of hydration of K+ and Cl corresponds to sum of lattice energy of KCl and heat of solution of KCl and is calculated as follows –

Sum of heat of hydration of K+and Cl ions =  -717 kJ/mol + 18

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