2. In the gas phase, AlCl3 is a molecular substance. A reaction of gaseous AlCl3 at high temperature — Stoichiometry, Hess's Law, Potential Energy Curves, Lewis Diagrams, VSEPR Theory, Equilibrium Chemistry Question
Problem Context
2. In the gas phase, AlCl3 is a molecular substance. A reaction of gaseous AlCl3 at high temperature is represented by the following balanced equation.
Reaction 1: AlCl3(g) → Al(g) + 3 Cl(g) ΔH1 = ?
(a) How many grams of Cl(g) can be formed from 1.25 mol of AlCl3(g) ?
Additional reactions that involve Al or Cl are shown in the following table.
(b) Calculate the value of ΔH1, in kJ/mol rxn, for reaction 1 above using reactions 2, 3, and 4.
(c) A potential energy diagram for Cl2 is shown in the following graph.
(i) Based on the graph, what is the bond length, in picometers, for Cl2 ?
(ii) A student finds that the average Al − Cl bond length is 220 picometers and the average bond energy is 425 kJ/mol. Draw the potential energy curve for the average Al − Cl bond on the preceding graph.
(d) Three proposed Lewis diagrams for the AlCl3(g) molecule are shown.
(i) The AlCl3(g) molecule has a trigonal planar geometry. Which diagram (1, 2, or 3) can be eliminated based on geometry? Justify your choice based on VSEPR theory.
(ii) Which of the three diagrams is the best representation for the bonding in AlCl3 ? Justify your choice based on formal charges.
AlCl3 is known to dimerize reversibly in the gas phase. The dimerization equilibrium is represented by the following equation.
2 AlCl3(g) ⇌ Al2Cl6(g)
(e) Write the expression for the equilibrium constant, Kp, for this reaction.
A particle-level diagram of an equilibrium mixture of AlCl3(g) and Al2Cl6(g) at 400°C in a 25 L closed container is shown.
(f) Using the particle-level diagram, calculate the value of Kp for the reaction if the total pressure in the container is 22.1 atm.