Question

The standard heat of combustion of solid Boron is equal to :-

• A. $\Delta H _{ f }^{ o }\left( B _{2} O _{3}\right)$
• B. $2 \Delta H _{ f }^{ o }\left( B _{2} O _{3}\right)$
• C. $\frac{1}{2} \Delta H _{ f }^{ o }\left( B _{2} O _{3}\right)$
• D. $4 \Delta H _{ f }^{ o }\left( B _{2} O _{3}\right)$

Answer 1

Answer: (C)

$B +\frac{3}{2} O _{2} \rightarrow \frac{1}{2} B _{2} O _{3}$
$\Delta H =\left(\Delta H _{ comb }\right)_{ B }^{ o }$
$\frac{1}{2}\left(\Delta H _{ f }^{ o }\right)_{ B _{2} O _{3}}$