[rinic]

The question gave you a reaction scheme, and since I can't remember what the compound was, I'll just denote it as compound X.

Compound X is catalyzed by HCl. The reaction rate, rate=k[X][HCl]. k=_____M-1 s-1 (I don't exactly remember k either). [X]= 0.50 M, [HCl]= 0.01 M.

What is the half life of compound X when HCl is added?

When I did this question, I couldn't understand how to incorporate the [HCl] value. By the question, it should be a second order question, not a pseudo first order so I just took the half life equation for second order, k, and [X] to solve it.  I'm just puzzled because I'm sure I actually needed to use the concentration for HCl somewhere.....δ

[clinz63]

I think it is pseudo first order since [HCl] does not change. It a catalyst after all. So you just need to calculate k' for the pseudo first order reaction and you're good to go.