Question

The heat of combustion of yellow phosphorous & red phosphorous are - 9.91 KJ and - 8.78 KJ respectively. The heat of transition of yellow phosphorous to red phosphorous is:

• A. - 18.69 KJ
• B. + 1.13 KJ
• C. + 18.69 KJ
• D. - 1.13 KJ

Answer 1

The correct option is D

- 1.13 KJ

The given equations for the combustions of different types of phosphorous are:
(y) $P_4+5O_2⟶P_4{O}_{10}-9.91KJ------\left(i\right)$
(R) $P_4+5O_2⟶P_4{O}_{10}-8.78KJ------\left(ii\right)$
Now when we subtract we get (i) - (ii) gives

​(y) $P_4⟶\left(R\right)P_4-1.13KJ$