Final answer:
The question deals with a zero-order reaction in a plug flow reactor, where the rate is constant and the concentration of substance A decreases linearly over time. This reaction behavior can be modeled by examining the thermal decomposition of ammonia on different surfaces, with a linear decay observed on a tungsten surface indicating zero-order kinetics.
Step-by-step explanation:
The student's question refers to the kinetics of a decomposition reaction of a pure substance A in a plug flow reactor. Understanding reaction kinetics is essential for predicting the rate at which reactants are converted to products and for the design of reactors in chemical engineering.
In the context of this question, a zero-order reaction is discussed. The rate of a zero-order reaction is constant and does not depend on the concentration of the reactant. Hence, the decrease in concentration of substance A with time will be linear, as indicated by the plot with a straight line that has a slope of -k where k is the rate constant. This phenomenon is evident in the decomposition of certain substances, such as the thermal decomposition of NH₃ (ammonia) in catalytic processes using different solid surfaces.
For instance, the decomposition of ammonia (NH₃) on a tungsten (W) surface exhibits zero-order kinetics with a linear concentration-time plot, unlike on a quartz (SiO₂) surface, where it shows first-order behavior with an exponentially decaying concentration-time plot. The rate of the reaction and the integrated rate law can be determined from the slope of the linear plot by estimating the concentrations at two different times and calculating the change in concentration over time.