a. Define standard enthalpy change of combustion.

b. When red phosphorus burns in oxygen the enthalpy change is –2967 kJ mol^–1. For white phosphorus the enthalpy change is –2984 kJ mol^–1. For both forms of phosphorus the reaction taking place is:
P₄(s) + 5O₂(g) → P₄O₁₀(s)

i. Use this information to calculate the enthalpy change for the transformation: P₄(white) → P₄(red).
ii. Represent these changes on an enthalpy profile diagram.