Question

4. For the reaction A+B → C+D we find that the rate law is v=k[A]”[B]° Which of the following mechanisms is consistent with the rate law? Explain in detail. a) A+B → C+D b) A+A ~ A2 (fast step) A2 +B → C+D (slow step) c) A+A → A2 (slow step) A2+B → C+D (fast step) d) A+A → A2 (fast equilibrium) A2+B → C+D (slow step)

Answer 1

Rate lau – In chemical kinetics, rate laus explains the dependence of rate of reaction on the concentration of species in reaction, It is defined as The rate of a reaction is directly proper- tional to the reactant concentration in which each term raised to some power which may or may not be equal to the stoichiometric coefficient of the reactant species Consider a general reaction aA + bB cC + dD a, b, c &d stoichiometric coefficient rate laus, rate & [A7² [B]Y и & ты м тлуу оut be equal to add respectively Rate = K[A]”[B7% It is determined enperimen Criven reaction. A+B - C + D . rate laws - K[A][B]°

find out. from the given option which of the following mechanism is consistent with the sale lani a) At B CAD rate law = K CAI'[B]' Since rate laws can be written with the help of enperiment, we supposed that its stoichiometric coefficient is equal to the power in each concentration term. ATA A fast step A + B cHD slow step rate for any reaction its rate can only be decided by the slowest step of that reaction rate enpression. V = K, [A] [A ] for fast step. V₂ = ke [A] [B ] slow step Ata A slow step. A + B CAD fast step. therefore, Rate enpression, v K[n]²) Slowest step. this is consistent with the given data

= K[n]² [B7° [since [B]° = 12 d) At A It A fast equilibrium A rate enpression [12] [A72 [A] = keq (A72 A₂ + B C + D slow steh rate expression. va k [2] [B] va k Keg [AT [B] va Knew [m]? (3] h Therefore the correct answer is option &