Question

For the given reactions $Si{O}_2+4HF\to Si{F}_4+2H_{2}O,\Delta H=-10.17Kcal$
$Si{O}_2+4HCl\to SiC{l}_4+2H_{2}O,\Delta H=36.7Kcal$.
It may be concluded that:

• A. $HF$ will attack $Si{O}_2$ and $HCl$ will not
• B. $HCl$ will attack $Si{O}_2$ and $HF$ will not
• C. $HF$ and $HCl$ both attack $Si{O}_2$
• D. none attacks $Si{O}_2$

Answer 1

Answer: (A)

$HF$ will attack $Si{O}_2$ and $HCl$ will not

$\Delta G=\Delta H-T\Delta S=-ve$
All exothermic reactions are spontaneous, hence $HF$ will attack $Si{O}_2$ but $HCl$ will not attack.