time required for [I] to decrease to half its initial value to the same time for

Question

time required for [I] to decrease to half its initial value to the same time for [Br] at 500 degree C. In some reactions there is a competition between kinetic control and thermodynamic control over product yields. Suppose compound A can undergo two elementary reactions to stable products: For simplicity we assume first-order kinetics for both forward and reverse reactions. We take the numerical values k1 = 1 times 108 s-1, k-1 = 1 times 102 s-1, k2 = 1 times 109 s-1, and k-2 = 1 times 104 s-1. Calculate the equilibrium constant for the equilibrium From this value, give the ratio of the concentration of B to that of C at equilibrium. This is an example of thermodynamic control. In the case of kinetic control, the products are isolated (or undergo additional reaction) before the back reactions can take place. Suppose the back reactions in the preceding example (k-1 and k-2) can be ignored. Calculate the concentration ratio of B to C reached in this case. Compare and contrast the mechanisms for the two gas-phase reactions H2 + Br2 rightarrow 2 HBr

Explanation / Answer

A B AC if we reverse 1st reaction BA AC if we combine above two equations B C k(B-C) = k-1 x k2 k(C-B) = k-2 xk1 now equilibrium const K = [C]/[B} =( k-1 xk2)/(k-2 xk1)

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