Question

The heats of combustion of yellow phosphorus and red phosphorous are –9.19 kJ and – 8.78 kJ respectively, then heat of transition of yellow phosphorus to red phosphorous is

• A. – 18.69 Kj
• B. +1.13 kJ
• C. +18.69 Kj
• D. – 1.13 kJ

Answer 1

Answer: (D)

– 1.13 kJ

Answer 2

(i) P₄ (yellow) +5O₂(g) → P₄O₁₀ + 9.19 kJ

(ii) P₄(red) + 5O₂(g) → P₄O₁₀ + 8.78 kJ

————————————————————

substracting, P₄(yellow) – P₄ (red) = 1.13 kJ

⇒ P₄(yellow) = P₄(red) + 1.13 kJ

So, heat of transition of yellow to red phosphorus is – 1.13 kJ