Question

The heats of combustion of yellow phosphorus and red phosphorus are $-9.91kJ$ and $-8.78kJ$ respectively. The heat of transition of yellow phosphorus to red phosphorus is:

• A. $-18.69kJ$
• B. $+1.13kJ$
• C. $+18.69kJ$
• D. $-1.13kJ$

Answer 1

The correct option is D $-1.13kJ$

Since the conversion reaction can be written as

$P_{\left(Yellow\right)}\to P_{\left(Red\right)}$

Hence, the heat of reaction of above reaction ($\Delta H$) can be written as,

$\Delta H=\text{heat of combustion of}{P}_{\left(Yellow\right)}-\text{heat of combustion of}{P}_{\left(Red\right)}=-9.91KJ-(-8.78KJ)=-1.13KJ.$

Hence, the answer is option D.