Ionic compounds vaporization

Ion pairs form when an ionic compound vaporizes. 

Ionic compounds typically have higher boiling points and lower vapor pressures than covalent compounds. Predict which compound in the following pairs has the lower vapor pressure at room temperature (a) CEO or Na,0 (b) InCl, or SbCl, (c) LiH or HC1 (d) MgCl, or PCI,. 

The properties of HF reflect the strong hydrogen bonding that persists even in the vapor state. As a result of its high polarity and dielectric constant, liquid HF dissolves many ionic compounds. Some of the chemistry of HF as a nonaqueous solvent has been presented in Chapter 10. Properties of the hydrogen halides are summarized in Table 15.9. 

Water h2o Clear, colorless liquid with low vapor pressure, highly polar Dissolving polar and ionic compounds... 

Reclaim cannot remove metals or other ionic compounds from groundwater nor catalyze chemical reactions. Also, the success of Reclaim is in relative proportion to the permeability of the geologic components comprising the contaminated site, the hydraulic gradient, and the concentrations and vapor pressures of the contaminants. As permeability, contaminant concentrations, vapor pressure, and hydraulic gradients decrease, so does the rate of recovery. In addition, Reclaim requires vendor-supplied, on-site service and support on a periodic basis. 

Covalent compounds generally have higher vapor pressure than ionic compounds. The fishy smell of fish arises from amines in the fish. Explain why squeezing lemon (which is acidic) onto fish reduces the fishy smell (and taste). 

As shown in Figure 1.2, the solvent strength of supercritical carbon dioxide approaches that of hydrocarbons or halocarbons. As a solvent, C02 is often compared to fluorinated solvents. In general, most nonpolar molecules are soluble in C02, while most polar compounds and polymers are insoluble (Hyatt, 1984). High vapor pressure fluids (e.g., acetone, methanol, ethers), many vinyl monomers (e.g., acrylates, styrenics, and olefins), free-radical initiators (e.g., azo- and peroxy-based initiators), and fluorocarbons are soluble in liquid and supercritical C02. Water and highly ionic compounds, however, are fairly insoluble in C02 (King et al., 1992 Lowry and Erickson, 1927). Only two classes of polymers, siloxane-based polymers and amorphous fluoropolymers, are soluble in C02 at relatively mild conditions (T < 100 °C and P < 350 bar) (DeSimone et al., 1992, 1994 McHugh and Krukonis, 1994). 

Desorption ionization methods are those techniques in which sample molecules are emitted directly from a condensed phase into the vapor phase as ions. The primary use is for large, nonvolatile, or ionic compounds. There can be significant disadvantages. Desorption methods generally do not use available sample efficiently. Oftentimes, the information content is limited. For unknown compounds, the methods are used primarily to provide molecular weight, and in some cases to obtain an exact mass. However, even for this purpose, it should be used with caution because the molecular ion or the quasimo-lecular ion may not be evident. The resulting spectra are often complicated by abundant matrix ions. 

Answer The correct answer is SrCl2(s) —> SrCl2(/). Melting a stable ionic compound will require much more energy than breaking most intermolecular forces, especially the vaporization of an alcohol, choice 2, and the melting of a soft metal like gold. 

As a result of their high boiling points, ionic compounds are rarely gaseous at room temperature, while many molecular compounds are. Ice, for example, will eventually melt and then vaporize. In contrast, salt will remain a solid no matter how long it remains at room temperature. 

Changes in oxidation number You may recall from previous chapters that the oxidation number of an atom in an ionic compound is the number of electrons lost or gained by the atom when it forms ions. For example, look at the following equation for the redox reaction of potassium metal with bromine vapor. 

Ionic compounds tend to have higher melting and boiling points and to be less volatile (that is, have lower vapor pressures) than covalent compounds. For each of the following pairs, use electronegativity differences to predict which compound has the higher vapor pressure at room temperature. 

From the very beginning of the studies of gas-phase radiochemistry, the experimental adsorption enthalpies were examined for a possible relationship with the macroscopic characteristics of volatility. Shortly after it was reported [2] that a few investigated chlorides showed heats of adsorption (evaluated somewhat differently than today) equal to about two-thirds of their heats of vaporization. This roughly linear correlation took place for both molecular and ionic compounds in the range of the vaporization heat from 40 to 200 kJ mol-1. Since then, the adsorption enthalpies have been reported in the literature for many more chlorides and oxychlorides. The... 

Consider the dissolution of an ionic compound such as potassium fluoride in water. Break the process into the following steps separation of the cations and anions in the vapor phase and the hydration of the ions in the aqueous medium. Discuss the energy changes associated with each step. How does the heat of solution of KE depend on the relative magnitudes of these two quantities On what law is the relationship based ... 

Generally, one expects that solutes which are liquids in their pnre form (snch as ethyl alcohol) will have some vapor pressnre of their own, whereas ionic compounds (such as sodium chloride) will not contribnte to the total vapor pressnre over the solntion. 

The calculation of lattice energies of ionic compounds is very important since, in general, there is no direct way to measure them experimentally, although they can be obtained from certain experimental data using the Born-Haber cycle which is discussed immediately below. For example, the heat of vaporization of NaCl does not give the lattice energy because up to the highest temperatures at which accurate measurements can be made the gas phase consists of NaCl molecules (or ion pairs), and it has so far proved impossible to get an accurate estimate of the heat of dissociation of NaCl(g) into Na+(g) and Cl (g) since NaCl(g) normally dissociates into atoms. 

The heats of formation of various ionic compounds show tremendous variations. In a general way, we know that many factors contribute to the over-all heat of formation, namely, the ionization potentials, electron affinities, heats of vaporization and dissociation of the elements, and the lattice energy of the compound. The Born-Haber cycle is a thermodynamic cycle that shows the interrelation of these quantities and enables us to see how variations in heats of formation can be attributed to the variations in these individual quantities. In order to construct the Born-Haber cycle we consider the following thermochemical equations, using NaCl as an example... 

The Born-Haber cycle is also valuable as a means of analyzing and correlating the variations in stability of various ionic compounds. As an example, it enables us to explain why MgO is a stable ionic compound despite the fact that the Mg2+ and O2- ions are both formed endothermally, not to mention the considerable energies required to vaporize Mg(s) and to dissociate 02(g). A Hf is highly negative despite these opposing tendencies because the lattice energy of MgO more than balances them out. 

In its pure form, sodium is used as a coolant in nuclear reactors and in sodium vapor lamps used for outdoor lighting. In its combined form in ionic compounds, you need only look on the contents list of consumer products to find a variety of sodium salts in the products you use and the foods you eat. 

Even the more volatile compounds—e.g., prometone—did not vaporize at all when such compounds were applied to surfaces in aqueous solution at pH levels of 2-3 (129). Ionic species vaporized less than molecular species. Since prometone was present primarily in the ionic form in the acid system, this was probably the case here. 

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