Question

The enthalpy of transition of crystalline boron to amorphous boron at ${1500}^{o}C$ is ${0.4kcalmol}^{-1}$. Assuming at.wt. of boron is 10, the change in enthalpy of transition (in ${kcalmol}^{-1}$) of 50 g boron from crystalline to amorphous form is ______.

Answer 1

Given the following conversion:

$B\left(crystalline\right)\to B\left(amorphous\right)$

$\Delta H_f^{transition}=0.4$ Kcal mol${}^{-1}$

This means that the enthalpy of transition of crystalline boron to amorphous boron is $0.4$ kcal.

So, the enthalpy of formation of $50$ g i.e. $5$ moles=$0.4\times 5=2$ kcal

Hence, the correct answer is $2$.