(a) In an experiment, 5.0 mmol Cl₂(g) was sealed into a reaction vessel of volume 2.0 L and heated to 1200. K, and the dissociation equilibrium was established. What is the equilibrium composition of the mixture? Use the information in Table 5G.2.

(b) If 5.0 mol Br₂ is placed into the reaction vessel instead of the chlorine, what would be the equilibrium composition at 1200. K? 

(c) Use your results from parts (a) and (b) to determine which is thermodynamically more stable relative to its atoms at 1200. K, Cl₂, or Br₂.

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TABLE 5G.2 Equilibrium Constants for Various Reactions Reaction T/K* H₂(g) + Cl₂(g) 2 HCl(g) H₂(g) + Brz(g) 2 HBr(g) H₂(g) + 1₂(g) 2 HI(g) 2 BrCl(g) Br₂(g) + Cl₂(g) 2 HD (g) H₂(g) + D₂(g) F₂(g) 2 F(g) Cl₂(g) = 2 Cl(g) Br₂(g) 2 Br(g) 1₂(g) 2 I(g) N₂(g) + 3 H₂(g) 2 NH₂(g) 2 SO₂(g) + O₂(g) - 2 SO₂(g) N₂O₂(g) 2 NO₂(g) 300 500 1000 300 500 1000 298 500 700 300 500 1000 100 500 1000 500 1000 1200 1000 1200 1000 1200 800 1000 1200 298 400 500 298 500 700 298 400 500 K 4.0 X 10³⁰ 4.0 X 10¹8 5.1 X 108 1.9 X 10¹7 1.3 X 10¹0 3.8 X 10 794 160 54 377 32 5 0.52 0.28 0.26 3.0 X 10-¹1 1.0 X 102 0.27 1.0 X 105 1.7 X 10³ 3.4 X 105 1.7 X 10³ 2.1 X 10 0.26 6.8 6.8 X 10² 41 3.6 X 102 4.0 X 10²4 2.5 X 10¹0 3.0 X 10 0.15 47.9 1.7 X 10³ K 4.0 X 10³¹¹ 4.0 X 10¹ 5.1 X 10² 1.9 x 10¹7 1.3 X 10⁰0 3.8 X 10 794 160 54 377 32 5 0.52 0.28 0.26 7.3 X 10-13 1.2 X 104 2.7 X 10³ 1.2 X 107 1.7 X 105 4.1 x 107 1.7 X 10 3.1 x 10-5 3.1 X 103 6.8 X 10² 4.2 X 10² 4.5 X 10¹ 62 9.9 X 10²5 1.0 X 10¹2 1.7 X 106 6.1 x 1023 1.44 41