The Molecular View

It is now a practice to use a variety of surface characterization techniques in the study of chemisorption and catalysis. The examples given here are illustrative most references in this section as well as throughout the chapter will contain results from several techniques. 

Restructuring of a surface may occur as a phase change with a transition temperature as with the Si(OOl) surface [23]. It may occur on chemisorption, as in the case of oxygen atoms on a stepped Cu surface [24]. The reverse effect may occur The surface layer for a Pt(lOO) face is not that of a terminal (100) plane but is reconstructed to hexagonal symmetry. On CO adsorption, the reconstruction is lifted, as shown in Fig. XVI-8. 

---

As we have seen, the third law of thermodynamics is closely tied to a statistical view of entropy. It is hard to discuss its implications from the exclusively macroscopic view of classical themiodynamics, but the problems become almost trivial when the molecular view of statistical themiodynamics is introduced. Guggenlieim (1949) has noted that the usefiihiess of a molecular view is not unique to the situation of substances at low temperatures, that there are other limiting situations where molecular ideas are helpfid in interpreting general experimental results ... 

After a drop of ink is added to a beaker of water (left), the ink diffuses slowly through the liquid (center) until eventually the ink is distributed uniformly (right). The molecular views indicate that the motion of ink molecules and water molecules is responsible for this diffusion. Ink molecules (red-violet circles) and water molecules (blue circles) move about continually, even after they are well mixed. 

Atoms and molecules are always moving, even when no visible changes take place. In our ink example, ink molecules move randomly in all directions. As the molecular view in Figure 2-8c indicates, however, the total number of ink molecules and water molecules in any region of the liquid does not change once the molecules are evenly distributed. As a result, there is no further change in color. 

Notice that the molecular view in Figure 3-20 includes Ions as well as neutral molecules. Molecular view means a view of how matter looks at the atomlc/molecular level. Thus, such Illustrations may contain Ions and individual atoms as well as molecules. 

The ideal gas equation and the molecular view of gases lead to several useful applications. We have already described how to cany out calculations involving P-V-n-T relationships. In this section, we examine the use of the gas equation to determine molar masses, gas density, and rates of gas movement. 

Because these are nonmetal oxides, they cannot be described as metallic. Neither oxide contains ions, so they must be network or molecular. The melting points provide the information needed to categorize the oxides, and the molecular views support the identifications. 

Ceramic oxide superconductors have distinct atomic layers. The Cu-containing superconductors contain planes of copper and oxygen atoms, as the molecular view shows. These planes alternate with layers containing oxygen and the other metals that make up the superconductor. Superconductivity takes place in the Cu—O planes. 

This molecular view of Figure 12-11 suggests that the extent of vapor pressure lowering will depend on the fraction of solvent molecules that has been replaced. In other words, the vapor pressure should be proportional to the mole fraction of the solvent. The molecular view also suggests that this effect does not depend on the nature of the solute, but only on its mole fraction. Experiments show that this is often the case, particularly for dilute solutions. A simple equation, Raoult s law, expresses this proportionality between vapor pressure and mole fraction V V /Jpuj-g solvent Raoulfs law states that the vapor pressure of a solution is the... 

Notice that over the same period the rate of O2 formation is only half the rate of NO2 consumption. This follows from the molecular view of the mechanism and from the stoichiometry of the reaction. The rate relationship among the three species involved in NO2 decomposition is given by the following expression ... 

When a reaction proceeds in a single elementary step, its rate law will mirror its stoichiometry. An example is the rate law for O3 reacting with NO. Experiments show that this reaction is first order in each of the starting materials and second order overall NO + 03- NO2 + O2 Experimental rate = i [N0][03 J This rate law is fully consistent with the molecular view of the mechanism shown in Figure 15-7. If the concentration of either O3 or NO is doubled, the number of collisions between starting material molecules doubles too, and so does the rate of reaction. If the concentrations of both starting materials are doubled, the collision rate and the reaction rate increase by a factor of four. 

The figure represents a molecular view of a gas-phase reaction that has reached equilibrium. Assuming that each molecule in the molecular view represents a partial pressure of 1.0 bar, determine for this... 

The molecular view represents a set of initial conditions for the reaction described in Example. Each molecule represents a partial pressure of 1.0 bar. Determine the equilibrium conditions and redraw the picture to illustrate those conditions. 

C18-0017. The molecular view below represents a small portion of a solution that matches Point A on the corresponding titration curve. Redraw the molecular picture to show how the figure should look for each of the points B-D along the titration curve. Your drawings should show any water molecules formed as part of the titration process. 

When a strip of zinc metal is dipped in a solution of copper(II) sulfate, zinc is oxidized to 7n (a >5 )1 and q) is reduced to copper metal. The insoluble metal precipitates from the solution, hi the molecular views, water moiecuies and spectator anions have been omitted for clarity. 

The challenge of understanding the effects resulting from the structure of the solvation complex continues to motivate large fields of chemistry and physics [76]. The molecular view of these phenomenon is important, particularly for under-... 

Water The Molecular View Intermolecular Forces in Water Water Physical Properties Revisited More Evidence for Water s Intermolecular Forces MiniLab 13.1 How many drops can you put on a penny ... 

With T-i lower than Tz, the most probable molecular speed u-, is less than U2. (Note the similarity to Figure 5.12) The fraction of molecules with enough energy to escape the liquid (shaded area) is greater at the higher temperature. The molecular views show that at the higher T, equilibrium is reached with more gas molecules in the same volume and thus at a higher vapor pressure. 

Various subclasses of liquid crystals have been described. " From the molecular view, Uquid crystals are built up of rod-hke stiff moieties in the molecule. This is also true for liquid crystal polymers (LCP)s. 

The molecular view of the balanced equation is shown in M FIGURE 3.5. 

Why are more molecules of I2 seen in the molecular view relative to the number of CI2 molecules ... 

M Figure 1.4 The three physical states of water are water vapor, liquid water, and ice. In this photo we see both the liquid and solid states of water. We cannot see water vapor. What we see when we look at steam or clouds is tiny droplets of liquid water dispersed in the atmosphere. The molecular views show that the molecules in the solid are arranged in a more orderly way than in the liquid. The molecules in the gas are much farther apart than those in the liquid or the solid. 

The following are molecular views of two different possible mechanisms by which an automobile air bag might function. One of these mechanisms involves a chemical reaction and the other does not. By looking at the molecular views, can you tell which mechanism operates via a chemical reaction ... 

Consider the molecular view of water shown here. Pick a molecule in the interior and draw a line to each of its direct neighbors. Pick a molecule near the edge (analogous to a molecule on the surface in three dimensions) and do the same. Which molecule has the most neighbors Which molecule is more likely to evaporate ... 

Consider the molecular views of osmosis cells. For each cell, determine the direction of water flow. 

Examine the molecular views of three different acid solutions shown here. Based on these views, which one of these acids is a weak acid ... 

Based on the molecular view of each acid solution, determine whether the acid is weak or strong. 

Consider the molecular views of an A1 strip and Cu solution. Draw a similar sketch showing what happens to the atoms and ions if the A1 strip is submerged in the solution for a few minutes. 

Consider the molecular view of an electrochemical cell involving the overall reaction ... 

Problem The molecular views below depict reactant solutions for a precipitation reaction (with ions shown as colored spheres and water omitted for clarity) ... 

NH3 for H2O in M(H20)4. The molecular views show the first exchange and the fully ammoniated ion. 

Based on the molecular views shown for each of the following substances, classify them as an element, a compound, a homogeneous mixture, or a heterogeneous mixture ... 

The top beaker contains a solid with a molecular view of the solid the molecular view depicts the closely packed, immobile atoms that make up the solid structure.The middle beaker contains a liquid with a molecular view of the liquid the molecular view depicts atoms that are close together but moving freely.The bottom beaker contains a gas with a molecular view of the gas the molecular view depicts atoms that are far apart and moving freely. 

---