Question

Using the reaction mechanism given below write a rate expression for the reaction shown.

Reaction: COCl₂(g) + Cl₂(g) → CO(g) + 2 Cl₂ (g)

Mechanism: Step 1 Cl₂ (g) ↔ 2 Cl (g) fast

Step 2 Cl (g) +COCl₂ (g) → COCl (g) + Cl₂ (g) slow

Step 3 COCl (g) + Cl (g) ↔ CO (g) + Cl₂ (g) fast

rate = ?

I think the rate should be k2 [Cl] [COCl₂] but I'm not sure if that's right.

Answer 1

Reaction: COCl₂(g) + Cl₂(g) → CO(g) + 2 Cl₂ (g)

Mechanism: Step 1 Cl₂ (g) ↔ 2 Cl (g) fast

Step 2 Cl (g) +COCl₂ (g) → COCl (g) + Cl₂ (g) slow

Step 3 COCl (g) + Cl (g) ↔ CO (g) + Cl₂ (g) fast

In a chemical reaction , the slowest step is the rate determining step, that is step 2.

In this step, it involves 1 mole of COCl₂ (g) so the rate of the reaction will depent upon 1 mole of COCl₂ (g)

Rate law be , rate , r = k[COCl₂ (g)]¹         where k - rate constant

                            r = k [COCl₂ (g)]