Final answer:
The decomposition of a gaseous feed of pure A in a plug flow reactor is determined to be a zero-order reaction based on the linear relationship displayed in the graphical data, where the reaction rate is independent of the concentration of the reactants.
Step-by-step explanation:
Reaction kinetics is a vital aspect of Chemistry that examines the rate at which chemical reactions occur and the factors affecting these rates. The question "A gaseous feed of pure A decomposes to give a variety of products in a plug flow reactor," refers to the kinetics of the reaction, which can follow different orders: first-order, second-order, zero-order, or more complex forms. To determine the reaction order, one must consider the relationship between the reaction rate and the concentration of reactants.
A first-order reaction is based on the rate being directly proportional to the concentration of one reactant. The integrated rate law for a first-order reaction shows that the plot of the natural logarithm of the concentration of the reactant ([A]) versus time (t) will yield a straight line with a slope equal to the negative of the rate constant (-k).
A second-order reaction can involve either the square of the concentration of one reactant or the product of the concentrations of two different reactants, resulting in a rate that is proportional to the concentration squared. An example is a dimerization reaction where two monomers combine to form a dimer.
In contrast, a zero-order reaction displays a rate that is independent of the concentration of the reactants, where the rate equals the rate constant (k). The integrated rate law for zero-order kinetics shows that the plot of the concentration of A versus time (t) is a straight line, making it a linear relationship with the slope equal to the negative of the rate constant (-k).
Therefore, based on the linear graphs given for the decomposition reactions on different surfaces, we can see that the decomposition of the reactant A on a tungsten surface follows zero-order kinetics as suggested by the linear plot of reactant concentration ([A]) versus time (t). This means that the correct answer to the multiple-choice question (MCQ) about the kinetics of the conversion of a pure gaseous feed of A is:
(c) Zero-order reaction.