Potential-energy curves for gaseous NaCl and HCl have been measured on the same axes…

CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties

Problem

Potential-energy curves for gaseous NaCl and HCl have been measured on the same axes (PEPE in kJ mol−1\text{kJ}\,\text{mol}^{-1} vs. rr in nm\text{nm}, zero at infinite separation). • NaCl: minimum PE=−790 kJ mol−1PE = -790\,\text{kJ}\,\text{mol}^{-1} at r=0.236 nmr = 0.236\,\text{nm}. • HCl: minimum PE=−432 kJ mol−1PE = -432\,\text{kJ}\,\text{mol}^{-1} at r=0.127 nmr = 0.127\,\text{nm}. For rr values substantially smaller than these minima, both curves rise sharply; the NaCl curve becomes positive at r≈0.16 nmr \approx 0.16\,\text{nm}, whereas the HCl curve becomes positive at r≈0.10 nmr \approx 0.10\,\text{nm}. (a) State the equilibrium bond length and bond energy for each molecule. (b) Describe two factors that account for the difference in bond energies between NaCl and HCl, making explicit reference to ionic versus covalent interactions. (c) For either molecule, explain qualitatively why the potential energy increases rapidly as r is compressed below the equilibrium value. (d) Predict qualitatively how replacing NaCl with KCl would affect the equilibrium bond length and bond energy. Justify your answer in terms of Coulombic interactions.

Related theory

Browse the problem library