Dissolving spontaneity

Because AG° is a positive quantity, SrCr04 does not dissolve spontaneously to form a 1M solution at 25°C (Figure 17.7). Suppose, however, the concentrations of Sr2+ and Cr042- are reduced to 0.0010 M ... 

Strontium chromate should, and does, dissolve spontaneously to form a 0.0010 M water solution. As you might expect, its solubility at 25°C lies between 1M and 0.0010 M, at about 0.0060 M. 

For lithium metal in 1 Af HC1, the observed facts are that the metal dissolves spontaneously and a gas bubbles out of the solution. From Appendix 3 we select the two half-reactions (notice that the half-reactions are already balanced in both charge and number of atoms) ... 

Because AG for the dissolving of a solute depends on the concentration of the solute, even if AG is negative at low concentrations, it may become positive at high concentrations (Fig. 8.25). A solute dissolves spontaneously only until AG = 0. At that point, dissolved and undissolved solute are in equilibrium—the solution is saturated. 

At the specimen surface, soft corroded layer was formed during immersion and the layer could be easily removed by wiping lightly with acetone-soaked paper and in some conditions this layer was dissolved spontaneously. The thickness of this layer was defined as corrosion depth x, and measured at various test conditions. As shown in Figure 5, corrosion depth increases linearly with time, and... 

An interesting example of the kinetic effect in semiconductor photocorrosion is photopassivation and photoactivation of silicon (Izidinov et al., 1962). Silicon is an electronegative element, so it should be dissolved spontaneously and intensively in water with hydrogen evolution. But in most of aqueous solutions the surface of silicon is covered with a nonporous passivating oxide film, which protects it from corrosion. The anodic polarization curve of silicon (dashed line in Fig. 20) is of the form characteristic of electrodes liable to passivation as the potential increases, the anodic current first grows (the... 

Nad dissolves spontaneously in water. Based upon the following reaction ... 

Notice that, except for nickel, the metals used to make corns have negative oxidation potentials. In other words, unlike most metals, platinum, gold, silver, mercury, and copper d< not oxidize (or dissolve) spontaneously under standard conditions in the piesence of aqueous H ... 

It is evident that certain spontaneous physical processes could be reversed if the complete conversion of heat into work could be achieved it will now be shown that similar considerations apply to chemical reactions. A piece of zinc, for example, will dissolve spontaneously in an aqueous solution of copper sulfate, according to the equation... 

Ammonium nitrate (NH4NO3) dissolves spontaneously and endothermically in water. What can you deduce about the sign of AS for the solution process ... 

Phosphorescent Oil. Dissolve 1 grain phosphorus in 1 ounce olive oil in a test tube by the heat of hot water, or add a larger < uautity to s[Pg.273]

Recall from Chapter 13 that most water-soluble salts have a positive A//°oin yet dissolve spontaneously ... 

Predict whether or not Sn will dissolve spontaneously in hydrochloric acid. To solve the problem it is necessary to separate the corrosion reaction... 

The calculated Gibbs free-energy using Eq. (2.48) is negative, indicating that the reaction inEq. (2.50) proceeds spontaneously as written. Therefore, Sn wUl dissolve spontaneously in hydrochloric acid. 

More so, the concentration of iron ions is also made equal to IM, reducing the log term in the equation to zero, and leaving E = E°. In this case, E° is found to be +0.44 V, which supports the fact that iron dissolves spontaneously in acid. Oxidation is the exact reverse of reduction the reduction potential is -0.44 V [6]. 

Consider the following facts Water freezes spontaneously at — 5°C and 1 atm, and ice has a more ordered structure than liquid water. Explain how a spontaneous process can lead to a decrease in entropy. Ammonium nitrate (NH4NO3) dissolves spontaneously and endothermically in water. What can you deduce about the sign of A5 for the solution process Calculate the equilibrium pressure of CO2 due to the decomposition of barium carbonate (BaC03) at 25°C. (a) Trouton s rule states that the ratio of the molar heat of vaporization of a liquid (AT/yap) to its boiling point in kelvins is approximately 90 J/K mol. Use the following data to show that this is the case and explain why Trouton s rule holds tme ... 

Polymer solutions are lyophilic or reversible colloidal systems, which implies that the polymeric material dissolves spontaneously with a decrease in the Gibbs energy of the system < 0. 

BSA quench 2% (w/v) BSA in PBS. Often it is convenient to prepare a 10% stock solution to be diluted as required. This can be prepared by carefully applying 10 g of dry powdered BSA to the surface of 100 ml PBS in a 100- to 200-ml beaker. Cover the beaker and then simply place it in the refrigerator, allowing the protein to dissolve spontaneously without any stirring. This will produce a golden yellow clear solution without clumps of BSA or formation of bubbles or froth. 

The described technique is applicable to chemically stable passive films that can be cathodically reduced. Some passive films dissolve spontaneously when the anodic polarization is interrupted. In that case, if one follows the evolution of the corrosion potential as a fimction of time one observes a transient that resembles that shown in Figure 6.18. The potential of the plateau, called the Flade potential, is indicative of the passivation potential. However, the length of the plateau depends on the corrosion rate and therefore does not permit to measure of the amount of oxide present. 

Solubility of polymers, that is, ability to dissolve spontaneously in low-molecular-weight solvent and to form thermodynamically stable molecular solutions, is determined by a delicate interplay between the gain in conformational entropy, translational and orientational entropy of solvating molecules of low-molecular-weight solvent, and enthalpy change upon polymer dissolution. Therefore, solubility of polymer in a particular solvent strongly depends on temperature. Usually, polymers with nonpolar monomer groups are more soluble in nonpolar solvents, whereas polymers whose... 

Many are either insoluble in the given solvent, or they dissolve spontaneously and form without exception crystalloidal solutions, e.g., sugar or sodium chloride in water, benzoic acid in alcohol, naphthalene in benzol, gold in mercury. 

Heat and work are both commonly recorded as calories, but they are not equivalent forms of energy. Heat is a degraded form of energy work can be converted into an equal amount of heat, but heat cannot be converted to an equal amount of work. The heat that is released by a reaction at constant pressure is —AH, and this is not necessarily the same as the maximum possible work, — AF. As examples, a number of compounds including trichloroacetic acid and ammonium sulfate dissolve spontaneously in water (AF negative) but cool the solution therefore, at constant temperature heat would be absorbed, and AH is positive. AF and AH may differ by plus or minus several thousand calories, as in the case of glycolysis, wWe AF is —35,000 cal. and AH is —24,000 cal., one-third less. ... 

If a piece of cis-(CH) film and a trip of lead are placed in 12 M HCIO, the (CH) is oxidized to [(CH) ] (y 0.1) according to equation (5) and the lead does not dissolve spontaneously to any significant extent. If, however, these two electrodes are now connected via an external wire, t ead dissolves, liberating electrons which are taken up by the [(CH) ] ion resulting in the net electrochemical reduc-... 

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