s at 120 K. a.… # The evaporation of a 120-nm film of n-pentane from a single crystal of aluminum oxide is zero order with a rate constant of 1.92 * 1013 molecules>cm2 # s at 120 K. a. If the initial surface coverage is 8.9 * 1016 molecules>cm2, how long will it take for one-half of the film to evaporate? b. What fraction of the film is left after 10 s? Assume the same initial coverage as in part a.

In the fascinating world of chemical reactions, zero order kinetics play an important role, particularly in processes like the evaporation of films on surfaces. Unlike first or second order reactions, where the rate depends on the concentration of one or more reactants, zero order reactions have a constant rate. This rate does not change regardless of the concentration of the reactant. For example, if n-pentane evaporates from aluminum oxide at zero order, it means that the film will disappear at a steady rate, as defined by its rate constant.

A helpful way to visualize this concept is to imagine a bath tub being drained at a constant rate; it doesn’t matter how much water is in the tub, the water level decreases at the same speed. This is a real-life example of zero order kinetics in action.

Chemical kinetics is all about the speeds, or rates, at which chemical reactions occur. It is a cornerstone in understanding chemical processes. By focusing on the factors that influence these rates—like temperature, concentration, and surface area—chemists can control and predict the behavior of reactions. For students grappling with exercises like the evaporation of n-pentane film, recognizing that the rate constant in the zero order reaction remains unchanged is key. This helps to streamline calculations and improves comprehension of how these reactions will proceed over time.

Surface coverage refers to how much of a surface is occupied by a particular substance. It's a critical concept when considering reactions that occur on surfaces, such as catalysis or film evaporation. The initial surface coverage is the starting amount of substance present; in the textbook exercise, it is the amount of n-pentane molecules per square centimeter on the aluminum oxide. This initial data point is vital for calculating how much of the film will remain at any given time during the evaporation process governed by zero order kinetics. The more comprehensive the initial coverage, the longer the evaporation process may take.

The process of thin film evaporation, such as with n-pentane on aluminum oxide, is a physical change where the substance transitions from a liquid to a vapor state. It's intriguing to note that this process, when happening under zero order kinetics, evades the typical expectation that a diminishing film would evaporate more slowly over time. Instead, it maintains a constant evaporation rate. This nuance can seem counterintuitive but is essential for students to understand kinetic concepts fully. Grasping this allows better predictions and calculations in coating technologies, materials science, and even the pharmaceutical industry.