Suppose that a gas-phase reaction has stoichiometry as given below. A + B X X +

Question

Suppose that a gas-phase reaction has stoichiometry as given below. A + B X X + A Y X + B Z These type(s) of reactions shown are: simultaneous opposing consecutive Write the differential rate equations with respect to the intermediate X and the product Z The overall rate of reaction is equal to the rate of formation for the product Z. Using the appropriate substitutions from parts b, find an expression for the overall rate of reaction. The intermediate X is formed slowly but consumed rapidly, and so its concentration is much less than the reactants and products. What assumptions can be made? Many heterogeneous catalysts function by adsorbing gas molecules onto the surface of a solid When CO chemisorbed on W is heated gradually, a substantial amount of gas is evolved in the temperature range 400-600 K and again in the range 1400-1800 K, but not much at other temperatures. What does this behavior suggest about the way CO is adsorbed on tungsten?

Explanation / Answer

The above reactions are consecutive reactions, since the product formed in turn reacts with A and B to give Y and Z respectively. Strictly speaking the reaction is autocatalytic reaction.

The rate of X is d(X)/dt = K1[A] [B]- K-1[X] –K2[X][A]-K3[X][B] =0 ( from pseudo steady state approximation)

Hence [X] = K1[A][B]/ (K-1+K2[A]+ K3[B]

Hence rate of formation of Z is dZ/dt= K3[X] [B] = K3K1[A][B]/ (K-1+K2[A]+ K3[B])

[CO] is adsorbed bytungstun.

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