The following mechanism has been suggested for the reactionbetween Cl 2 and CHCl

Question

The following mechanism has been suggested for the reactionbetween Cl2 and CHCl3

Cl2 = 2Cl(g)

with equilibrium constant K (fast)

CHCl3(g) + Cl(g) --> CCl3(g) +HCl(g)

with rate constant k2 (slow)

CCl3(g) + Cl(g) --> CCl4(g)

with rate constant k3 (fast)

The rate law for this mechanism is

A. rate = k2[CHCl3(g)]

B. rate =k2K[CHCl3(g)][Cl2]0.5

C. rate =k2K0.5[CHCl3(g)][Cl2]0.5

D. rate = k3[CCl3(g)][Cl]

E. rate = k2[CHCl3(g)][Cl]

Why is it C?

Cl2 = 2Cl(g)

with equilibrium constant K (fast)

CHCl3(g) + Cl(g) --> CCl3(g) +HCl(g)

with rate constant k2 (slow)

CCl3(g) + Cl(g) --> CCl4(g)

with rate constant k3 (fast)

Explanation / Answer

The second step is the rate-determining step since it is theslowest. The first step produces 2 moles of Cl, but for the secondstep we only need 1 mole. So we want the rate of the first step tobe half as fast since we can only use half as much. This is thereason for K0.5. Since we only need half as much Cl, wealso need the concentration of Cl2 to be half as muchsince that is what produces the Cl. Hence,[Cl2]0.5.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.