Exothermic dissolving

CIO2 dissolves exothermically in water and the dark-green solutions, containing up to 8g/l, decompose only very slowly in the dark. At low temperatures crystalline clathrate hydrates, C102.nH20, separate (n 6-10). Illumination of neutral aqueous solutions initiates rapid photodecomposition to a mixture of chloric and hydrochloric acids ... 

I.ithium sulfate dissolves exothermically in water, (a) Is the enthalpy of solution for Ei,S04 positive or negative ... 

Frozen mixtures of trinitromethane -2-propanol (9 1) exploded during thawing. The former (of positive oxygen balance) dissolves exothermally in the alcohol, the heat effect increasing directly with the concentration above 50% w/w. Traces of nitric acid may also have been present. 

To understand the dissolution of ionic solids in water, lattice energies must be considered. The lattice enthalpy, A Hh of a crystalline ionic solid is defined as the energy released when one mole of solid is formed from its constituent ions in the gas phase. The hydration enthalpy, A Hh, of an ion is the energy released when one mole of the gas phase ion is dissolved in water. Comparison of the two values allows one to determine the enthalpy of solution, AHs, and whether an ionic solid will dissolve endothermically or exothermically. Figure 1.4 shows a comparison of AH and A//h, demonstrating that AgF dissolves exothermically. 

Whereas LiCl and CsF with disparate ionic radii dissolve exothermally in water, most halides of the alkaline metals dissolve without much heat evolution. This is a remarkable observation in view of the huge Madelung energy —1.74/(rM + rx) in atomic units (14.3 eV/A) relative to gaseous M+ and X- and it was first pointed out by Fajans183 that this is compatible with the approximate equality... 

Which chemical dissolved endothermically Which chemical dissolved exothermically ... 

Why do some solids dissolve exothermically, while other solids dissolve endothermically What factors may be involved Research two factors lattice energies and solvation energies. Go to the web site above. Go to Science Resources, then to Chemistry 11 to find out where to go next. Report your results to the class. 

Calcium bis[tetrahydroborate(l —)] is obtained as a fine powder which must be stored in well-sealed containers. It is stable in dry air at room temperature but traces of moisture decompose it with liberation of hydrogen. The gas evolution is quantitative when dilute hydrochloric acid is added. The compound decomposes at ca. 260°. The solvate Ca[BH4]2 -2THF loses THF on heating to 240° in vacuo. Calcium bis[tetra-hydroborate(l —)] dissolves exothermally in THF and crystalline Ca[BH4]2 -2THF may be isolated from the solution. The Ca[BH4]2 2THF is very soluble in dimethyl sulfoxide, in hexamethylphosphoric triamide, and in bis(2-methoxyethyl) ether (diglyme). 

Beryllium chloride is prepared by passing CCLt over BeO at 800°C. On a small scale the pure chloride and bromide are best prepared by direct interaction in a hot tube. The white crystalline chloride (mp 405°C) dissolves exothermically in water from HC1 solutions the salt [Be(H20)4]Cl2 can be obtained. Beryllium chloride is readily soluble in oxygenated solvents such as ethers. In melts with alkali halides, chloroberyllate ions [BeCl4]2 may be formed, but this ion does not exist in aqueous solution. 

When the acetic acid solutions of cyclohexanol and dichromate were mixed at 25°C rather than at 15°C the yield of crude cyclohexanone was only 6.9 g. A clue to the evident importance of the initial temperature is suggested by an experiment in which the cyclohexanol was dissolved in 12.5 mL of benzene instead of 10 mL of acetic acid and the two solutions were mixed at 15°C. Within afew minutes orange-yellow crystals separated and soon filled the flask the substance probably is the chromate ester, (CsHnOfjCrOj. When the crystal magma was let stand at room temperature the crystals soon dissolved, exothermic oxidation proceeded, and cyclohexanone was formed in high yield. Perhaps a low initial temperature ensures complete conversion of the alcohol into the chromate ester before side reactions set in. 

In contrast to the silicates, most carbonate and many sulfate minerals dissolve exothermically (AW ° < 0). This makes them most soluble at low temperatures and gives them a tendency to precipitate as temperature increases (Fig. 1.7). (Compare log versus /T curves for calcite and quartz in Fig. 1,7.) Thus, calcite (AW° = -2.30 kcal/mol) can be a troublesome precipitate on the walls of boiler systems where its thermal insulating properties prevent heat exchange and can seriously damage boiler performance. 

When hot or cold packs for sports injuries are activated, a solute that dissolves exothermically in the case of a hot pack, or endothermically in the case of a cold pack, dissolves in water. Hot packs generally use calcium chloride, CaCb, and cold packs generally use ammonium nitrate, NH4NO3. 

Instant hot and cold packs create aqueous solutions that form exothermically or endothermically and therefore release or absorb heat. A hot pack generates heat when a salt such as calcium chloride dissolves in water that is stored in the pack. The calcium chloride dissolves exothermically. A cold pack absorbs heat when a salt such as ammonium nitrate dissolves in water. The ammonium nitrate dissolves endothermically. 

Which of the solids that you tested dissolve exothermically Which dissolve endothermically ... 

MiniLab 1 Which factor—entropy, added heat, or both—promotes the dissolution in water of a solid that spontaneously dissolves endothermically Which factor promotes dissolution in water of a solid that spontaneously dissolves exothermically ... 

Energy Changes in Chemicai Reactions Exothermic and Endothermic Reactions Heat Forces That Drive Chemical Reactions MiniLab 20.1 Dissolving—Exothermic or Endothermic 708... 

What s periodic about atomic radii 262 20.1 Dissolving—Exothermic or ... 

Dissolves exothermically in water with extensive hydrolysis to colloidal stannic acid miscible in all proportions with CS 3. 

You are designing an instant heat pack for a food application. Your design includes a nontoxic ionic salt that dissolves exothermically in water. You need to control the amount of heat released. Initial prototypes get too warm, even with a fairly small amount of salt used. What else could you do to reduce the heat released in your product Identify any key limitations that would have to be met. 

Method To a suspension of p-toluenesulfonamide (24.3 g, 0.14 mol) in MeOH (30 ml), NaOMe (30 wt. % in MeOH, 37.9 g) was added, and the mixture was stirred at room temperature. p-Toluenesulfonamide was dissolved exothermically to give the sodium salt. After the addition of dimethylcarbonate (15.2 g, 0.17 mol), the mixture was refluxed for 18 h. The volatiles and excess dimethylcarbonate were evaporated. The residue was dissolved in water and the solvent was adjusted to pH 2 with cone HCl (23 g). The resulting precipitate was filtrated to give the reagent (30.9 g, 95% yield). 

The inner bag of the instant hot compress contains calcium chloride,CaCl2.When the inner bag is broken,the CaCl2 dissolves exothermically in water (heat is released).The instant cold compress contains an inner bag of ammonium nitrate, NH4NO3, which when broken apart allows the NH4NO3 to dissolve in the water in the outer bag.The solution process is endothermic (heat is absorbed),so the bag feels cold. 

The adsorption of H is conveniently described in terms of simplified one dimensional potential energy curves for an H2 molecule and for 2H atoms on a metal surface (Fig. 1). Far from the surface the two curves are separated by the heat of dissociation Ed = 218 kJ/mol H. The flat minimum in the H2 + M curve corresponds to physisorbed H2 (heat of physi-sorption Ep 10 kJ/mol H) and the deep minimum in the 2H + M curve describes chemisorbed H (heat of chemisorption E 50 kJ/mol H). If the two curves intersect above the zero energy level, the chemisorption requires an activation energy E. In further steps the chemisorbed H atoms penetrate the surface and are then dissolved exothermically or endothermically in the bulk where hydrides can be formed. There is now experimental and theoretical evidence that not all chemisorbed H necessarily stays on top of the first metal atom layer, but also below it as a so called subsurface H (two step chemisorption). 

In the preparation of nickel nitrate hydrazine [Ni(N03)2(N2H4)3] stoichiometric amounts of ammonium nitrate in hydrazine hydrate and nickel metal powder are allowed to react in the ratio of 2 3 1, respectively, at room temperature. The nickel metal dissolves exothermically with the evolution of hydrogen. The solid compound is obtained in 97% yield by the addition of alcohol. 

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