Question

The enthalpies of formation of group 2 oxides are quite high (highly negative) and, consequently, they are stable to heat. Which of the following is the most stable ?
A. BeO
B. MgO
C. CaO
D. SrO

Answer 1

Correct Answer - C
Calcium oxide has the most negative `Delta_(f)H^(@)`:
`{:("Metal oxide",BeO,MgO,CaO,ScO,BaO),(Delta_(f)H^(@)(kJmol^(-1)),-550,-601,-635,-590,-545):}`
As a result, these oxides have high melting point (BeO approx. `2500^(@)C` MgO approx `2800^(@)C`) very low vapor pressures, are good condutors of heat, chemically inert, and are electrical insulators Because of these factors, these oxides are used as refractory materials (materials not damaged by heating to high temperaure) an are useful for lining surface.