Textbook Q5.35

[Ava 1D]

Hi- I wasn't sure how to interpret this graph to formulate a balanced chemical equation for part A. If someone could explain how they got the values in pKa for A,B,C that would be great. thanks!

[Megan Mitchell 2B]

The y-axis in this graph is not pKa, but rather kPa - kilopascals, a unit of pressure and thus proportional to the amount of each reagant. The graph of A decreases in value, so we can assume that A is used up in this reaction and is thus a reactant. But C and B increase over the course of the reaction, so they are the products. Since A decreases from about 27.5 to about 17.5, its partial pressure decreased by 10 kPa. B increased by 5 kPa and C increased by 10 kPa. The moles of reactants and products are directly proportional to their partial pressures, so the ratio of the stoichiometric coefficients is 10:5:10, simplified to 2:1:2. Thus the balanced equation is 2A (g) --> B (g) + 2 C (g).

[Ava 1D]

Ah- that makes sense, thank you! (oops I just made a typo for the kPa unit, but thank you for clarifying!)