The standard heat of combustion of a solid boron is equal to:

Options

A. `DeltaH_(f)^(@)(B_(2)O_(3))`
B. `1//2DeltaH_(f)^(@)(B_(2)O_(3))`
C. `2DeltaH_(f)^(@)(B_(2)O_(3))`
D. `1//2DeltaH_(f)^(@)(B_(2)O_(3))`

Answer

B

Explanation

Combustion reaction of solid boron
`B(s)+(3)/(4)O_(2)(g)rarr(1)/(2)B_(2)O_(3)(s)`
`Delta H_(r )^(o)=Delta H_(c )^(o)=(1)/(2)DeltaH_(f)^(o)(B_(2)O_(3),s)-Delta H_(f)^(o)(B,s)-(3)/(4)Delta H_(f)^(o)(O_(2),g)`
`Delta H_(f)^(o)` of element in stable state of aggregation is assumed to be zero.
`DeltaH_(c )^(@)=(1)/(2)Delta H_(f)^(o)(B_(2)O_(3),s)`