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Need help asap - There is an error in the rate-determining step of the following proposed mechanism.

Slow step: CH3(g) + Cl2(g) → CH3(g) + HCl(g) and the rate rule is k1 = [CH4][Cl2]
Fast step: CH3(g) + Cl2(g) → CH3Cl(g) + Cl–(g) and the rate rule is k2 = [CH4][Cl2]
Overall : CH4(g) + 2Cl2(g) → CH3Cl(g) + HCl(g) + Cl–(g)

Which shows the correct rate-determining step for the mechanism?

CH4(g) + 2Cl(g) → CH3Cl(g) + HCl(g) + Cl–(g)
CH4(g) + Cl2(g) → CH3(g) + HCl(g) and the rate rule is k1 = [CH4][Cl2]
CH4(g) + Cl2(g) → CH3Cl(g) + Cl–(g) and the rate rule is k2 = [CH4][Cl2]
CH3(g) + 2Cl2(g) → CH3Cl(g) + Cl–(g) and the rate rule is k2 = [CH4][Cl2]

User Dan Morgan
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1 Answer

3 votes

Answer:

CH4(g) + Cl2(g) → CH3(g) + HCl(g) and the rate rule is k1 = [CH4][Cl2]

Step-by-step explanation:

Firstly, we must remember that the substitution reaction between halogens and alkanes to yield halogenoalkanes does not proceed by ionic mechanism rather it proceeds by free radical mechanism.

Now, if we look at the rate determining step as shown in the question, the elementary reaction equation of that step is not balanced.

Hence, the correct elementary reaction equation for the rate determining step and the rate law is; CH4(g) + Cl2(g) → CH3(g) + HCl(g) and the rate rule is k1 = [CH4][Cl2]

User Nick Martin
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