Question

The heat of combustion of yellow phosphorous is $-9.9kJ$ and of red phosphorous is $-8.78kJ$. The heat of transition of yellow phosphorus to red phosphorus is:

• A. $-9.91kJ$
• B. $-8.78kJ$
• C. $-9.37kJ$
• D. $-1.13kJ$

Answer 1

Answer: (D)

$-1.13kJ$

$P\left(red\right)+\frac{5}{2}{O}_2\to P_2{O}_5;△H=-8.78$

$P\left(yellow\right)+\frac{5}{2}{O}_2\to P_2{O}_5;△H=-9.91$

Substracting
$P\left(Red\right)+\frac{5}{2}{O}_2-P\left(Yellow\right)-\frac{5}{2}{O}_2\to P_2{O}_5-P_2{O}_5$

$P\left(Red\right)-P\left(Yellow\right)=0$;

$△H=-8.78+9.91=-1.113$

$P\left(Red\right)\to P\left(Yellow\right)△H=-1.13$

$P\left(Yellow\right)\to P\left(Red\right)△H=-1.13kJ$

Hence, option D is correct