Effect of Pressure on the Initial Rate

Apple96

Hi,

Let's suppose an elementary reaction of the low-pressure mixture has the initial reaction rate of x (2A + B --> A2B). What would be the initial reaction rate of the high-pressure mixture? (Imagine a mass M is placed upon the beaker filled with the mixture, and a mass 3M is placed upon another beaker).

I'm really not sure how to approach this problem. Yes, more pressure means more concentration (exactly 3 times), but I'm not sure how this affects the initial rate. Concentration can be used to compare the reaction rate of molecules involving in one equation (like 2A+ B --> A2B, the reaction rate of A will be twice as much as that of B). But, between the two different system? I'm really not sure. Please help!

Thank you,