Question

The heats of combustion of yellow phosphorous are $-9.19kj$ and $-8.78kJ$ respectively, then heat of transition of yellow phosphorous to red phosphorous is:

• A. $-18.69$ kJ
• B. $+0.41$ kJ
• C. $+18.69$ kJ
• D. $-0.41$ kJ

Answer 1

The correct option is D $-0.41$ kJ

Solution:- (D) $-0.41kJ$

The transition of yellow phosphorous to red phosphorous-

$P_{\text{yellow}}⟶P_{\text{red}}\Delta H=?$

Given:-

$P_{\text{yellow}}+{O_2}_{\left(g\right)}⟶\text{product}\Delta H=-9.19kJ.....\left(1\right)$

$P_{\text{red}}+{O_2}_{\left(g\right)}⟶\text{product}\Delta H=-8.78kJ$

$\text{product}⟶P_{\text{red}}+{O_2}_{\left(g\right)}\Delta H=8.78kJ.....\left(2\right)$

Adding ${eq}^n\left(1\right)\&\left(2\right)$, we have

$P_{\text{yellow}}+{O_2}_{\left(g\right)}+\text{product}⟶\text{product}+P_{\text{red}}+{O_2}_{\left(g\right)}\Delta H=(-9.19)+8.78kJ$

$P_{\text{yellow}}⟶P_{\text{red}}\Delta H=-0.41kJ$

Hence the heat of transition of yellow phosphorous to red phosphorous is $-0.41kJ$.