Answer to Question #139119 in General Chemistry for Flame

Question

When phosphorus is reacted with an excess oxygen, tetraphosphorus decaoxide, P4O10 is formed as shown in the following reaction:

4P (s) + 5O2 (g) ⎯→ P4O10 (s)

Consider the following thermochemical equations:

2PCl3 (l) + O2 (g) ⎯→ 2POCl3 (l) ΔH1 = –587 kJ

P4O10 (s) + 6PCl5 (s) ⎯→ 10POCl3 (l) ΔH2 = –419 kJ

2P (s) + 3Cl2 (g) ⎯→ 2PCl3 (l) ΔH3 = –686 kJ

2P (s) + 5Cl2 (g) ⎯→ 2PCl5 (s) ΔH4 = –892 kJ

i.Calculate the heat of formation of P4O10.

ii. Predict the driving force to produce P4O10 (spontaneous or non-spontaneous) in which ΔG for this reaction changes with the increase of temperature. Explain your answer.

Answer 1

i). The heat of formation of P4O10.

( (-587)+(-419)+ (-686)+ (-892)

= -2584kj

ii). Spontaneous reactions are accompanied by an increase in overall entropy, or disorder. You can qualitatively predict if a reaction will have an increase in entropy by looking at phase change, temperature change, change in the number of moles in a chemical reaction, and an increase in volume.