The following mechanism has been proposed for the gas-phase reaction of chloroform (CHCl3) and chlorine:

Step 1: Cl2 (g) ⇌2Cl (g) (fast)

Step 2: Cl (g) + CHCl3 (g) →HCl (g) + CCl3 (g) (slow)

Step 3: Cl (g) + CCl3 (g) →CCl4 (fast)

What is the overall rate constant?

The question is asking to compute the overall rate constant of the said gas phase reaction of chloroform (CHC13) and chlorine, base on the fact, I would say that the answer would be R = k [Cl] [CHCl3]. I hope you are satisfied with my answer and feel free to ask for more