textbook problem 5.I.13 part c

[sanaz ahmadi- 2H]

This question asks whether Cl2 or F2 is more stable, but how would we know based on the information we solved for in parts a and b?

[Sam Leistiko 2B]

In parts A and B, you calculated the equilibrium composition of the two reactions. In any reaction, greater stability of a molecule means that it requires more energy to break the bonds in that molecule, meaning less of that molecule will react at a given temperature. Because the two reactions in this problem occur under the same conditions, we can evaluate the stability of the molecules based on how many moles of the product are present at equilibrium. Whichever molecule has more moles of product present at equilibrium is more reactive, and therefore less stable. In this case, there was more F at equilibrium than Cl at equilibrium, meaning that Cl2 is more stable than F2, and therefore does not proceed as far to the right under the same conditions.

However, you do not actually need your results from part a and b to solve this question. You can simply look at the equilibrium constant K for a given reaction under certain conditions. A larger K value indicates that a reaction proceeds further to the right and produces more product than another reaction under the same conditions with a smaller K value. Because the K value for the reaction of F2 under the given conditions is larger than the K value for the reaction of Cl2 under the given conditions, we know that the F2 reaction forms more products. This means that the F2 molecule is more reactive, and therefore less stable.