[elliotyang]

The Pt-catalyzed decomposition of HI obeys the rate law dP_HI/dt = k1, at high pressure, with k₁ = 500 mm Hg/sec at 100^oC. At low pressures, the rate law becomes dP_HI/dt = k₂P_HI, with k₂ = 50sec^-1 at 100^oC. Calculate the HI pressure at which the value of dP_HI/dt should be 250 mmHg/sec at 100^oC.

Assume that HI is adsorbed on the catalyst according to the Langmuir equation

   *HI = kP_HI/*(1+bP_H2)   

where  * is the fraction of surface covered by adsorbed HI.

I got no idea how to start this problem.