Instructions: Put your name, social security number, and section number on the top of this exam page. Answer the following three (3) parts in the notation and conventions of the lecture for a total of 100 points. Read the entire exam. Work alone and consult no one, living or dead, about this test (except Brucat) until after you leave the room. Notebooks, textbooks and any other study material is not allowed in the exam room. You may use only your writing and calculating instruments; sharing of calculators is NOT allowed. Show work where appropriate and write only on this exam page. Show proper units to receive credit. Your name on this exam states the assertion: I hereby pledge that I have neither given nor received any unauthorized aid on this exam.

A mixture of 0.71 mol of N₂ and 1.20 mol of H₂ are placed in a 3.0 liter vessel at 900K. When the reaction

N_{2 (g)} + 3H_{2 (g)} <-> 2NH_{3 (g)}

reaches equilibrium, the concentration of hydrogen gas is found to be [H₂] = 0.100 M.
What is the number of moles of H₂ in the reaction vessel at equilibrium?

What is the number of moles of N₂ in the reaction vessel at equilibrium?

What is the number of moles of Ammonia in the reaction vessel at equilibrium?

What is the total pressure of the vessel at equilibrium?

Qualitatively, what is the effect on the reaction equilibrium upon doubling reactor vessel pressure at constant temperature by the addition of Helium gas. (Hint: the vessel volume remains unchanged).

Qualitatively, what is the effect on the reaction equilibrium of doubling the temperature at constant pressure. (Hint: the reaction is exothermic as written)

Part II (20 points each for a total of 40 points)

Consider the reaction

XeF₂ + F₂ <-> XeF₄ : K_C = 3.17 at 300 K.

a) (20 points) Write the equilibrium expression at 300 K for this reaction.

(20 points) A mixture of 0.52 moles of XeF₂ and 1.12 moles of F₂ are introduced into a 2.5 liter vessel. What is the equilibrium concentration, in moles per liter of XeF₄ at 300 K?

Part III (30 points)

Consider the reaction A <-> B where the following thermodynamic data is known:

H_rxn ⁰ = -14.0 kJ/mol

S_rxn ⁰ = -55.0 J/K^.mol

At what temperature does this reaction have an equilibrium constant of 1.00?
(Hint: Consider the standard enthalpy and entropy changes for this reaction to be temperature independent)