Question

1. The rate of formation of carbon tetrachloride from chloroform,

CHCl₃(g) + Cl₂(g) => CCl₄(g) + HCl(g)

is first order in CHCl₃ and half order in Cl₂.

Which step of the proposed mechanism must be slow in order to agree with this rate law?

1. Cl₂(g) => 2 Cl(g)
2. Cl(g) + CHCl₃(g) => HCl(g) + CCl₃(g)
3. CCl₃(g) + Cl(g) => CCl₄(g)

	1.	1
	2.	2
	3.	3

2. The proposed mechanism for a reaction is

Cl₂ => 2 Cl Fast

Cl + H₂S => HCl + HS Slow

Cl + HS => HCl + S Fast

Which of the following would be a rate law for the reaction?

	1.	rate = k[Cl2]1/2[H2S]
	2.	rate = k[Cl-][H2S]
	3.	rate = k[Cl2][H2S]
	4.	rate = [HCl][HS-]
	5.	rate = k[Cl2]

3. The proposed mechanism for a reaction is

O₃ => O₂ + O      Slow

O + NO => NO₂    Fast

Which of the following would be a rate law for the reaction?

	1.	rate = k[O][O2]
	2.	rate = k[NO][O]
	3.	rate = k[NO][O3]
	4.	rate = k[NO2][O2]
	5.	rate = k[O3]

Answer 1

Ans 1 : 2)

The order of CHCl3 is 1 and that of Cl2 is half.

the rate law for the reaction will be given as :

rate = k[CHCl₃] [Cl₂]^1/2

The second reaction : Cl(g) + CHCl₃(g) => HCl(g) + CCl₃(g) must be slow in order to agree with this rate law , since the order of species in the rate law coincide with the stoichiometric coeffecients of the reactant species in this reaction step.