AAMC Sample B/B #15

[jeep1010]

I don't understand the explanation, could someone possibly clarify this? I don't understand what they mean by "other equilibria". I chose D because I thought to carbonic anhydrase which would dissociate H2Co3 --> H+ + HCO3-.

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[Pono_0001]

I haven't studied acid yet. But I wouldn't pick D because enzyme is about kinetics, i.e. rate, and this is a problem on equilibrium. You can ignored the part about other equilibria. it's basically saying that H+ is kept low in the blood by some mechanisms unknown to you. it's just another way of saying the products are kept low and it's a hint for using le Chatelier

 

[aldol16]

Recall that enzymes only lower the kinetic barrier of activation. In other words, they make both the forward and reverse reactions more favorable. Put another way, all enzymes do is help the system get to equilibrium faster. And the equilibrium is the one denoted in the question. Your equilibrium constant does not change if you add an enzyme. If your equilibrium constant is small to begin with, it will remain small. So adding an enzyme wouldn't actually help it fully dissociate. It would just help that minuscule amount that would dissolve, dissolve quicker.

What A is saying is that H+ is always kept low so that equilibrium is driven to the right. In other words, say a molecule of HA dissociates. What A is saying is that the H+ produced is then removed by some other means. This then creates stress on the system to generate more H+, by dissociating HA.