4. White phosphorus, P4(g), can decompose into P2(g) at elevated temperatures. A balanced chemical e — Bond Length, Chemical Equilibrium, Thermodynamics Chemistry Question
Problem Context
- White phosphorus, P4(g), can decompose into P2(g) at elevated temperatures. A balanced chemical equation, Kp expression, and Lewis diagrams for the chemical species involved in the reaction are given.
(a) The average bond length in P4 molecules is 221 pm, whereas the average bond length in P2 molecules is 189 pm. Explain why the average bond length in P4 is greater than the average bond length in P2.
(b) A sample of P4(s) is placed in a sealed rigid container and heated to 1600 K, at which point the initial partial pressure of P4(g) is 0.470 atm. Some of the P4(g) decomposes into P2(g) as the system reaches equilibrium. At equilibrium, the partial pressure of P2(g) is determined to be 0.630 atm.
Calculate the value of the equilibrium constant, Kp, for the reaction at 1600 K. Show the work that leads to your answer.
(c) The reaction is thermodynamically favorable under standard conditions only at temperatures above 1500 K. A student claims that the reaction must be endothermic because it is favorable only at high temperatures. Do you agree or disagree? Justify your answer using ΔS°rxn and ΔG°rxn.