Consider the reaction :

Cl₂(aq) + H₂S(aq) → S(s) + 2H⁺ (aq) + 2Cl^– (aq)

The rate equation for this reaction is rate = k [Cl₂] [H₂S]

Which of these mechanisms is/are consistent with this rate equation?

(A) Cl₂ + H₂S $$\to$$ H⁺ + Cl^– + Cl⁺ + HS^– (slow)

Cl⁺ + HS^– $$\to$$ H⁺ + Cl^– + S (fast)

(B) H₂S $$ \Leftrightarrow $$ H⁺ + HS^– (fast equilibrium)

Cl₂ + HS^– $$\to$$ 2Cl^– + H⁺ + S (slow)

The half life period of a first order chemical reaction is 6.93 minutes. The time required for the completion of 99% of the chemical reaction will be (log 2=0.301) :

For a reaction $${1 \over 2}A \to 2B$$ rate of disappearance of ‘A’ is related to the rate of appearance of ‘B’ by the expression

The energies of activation for forward and reverse reactions for A₂ + B₂ $$\leftrightharpoons$$ 2AB are 180 kJ mol⁻¹ and 200 kJ mol⁻¹ respectively. The presence of catalyst lowers the activation energy of both (forward and reverse) reactions by 100 kJ mol⁻¹. The enthalpy change of the reaction ( A₂ + B₂ $$\to$$ 2AB) in the presence of catalyst will be (in kJ mol⁻¹)