Solids changes

Melting Point (MP) — the temperature at which a solid changes to a liquid. The melting point is not particularly sensitive to atmospheric pressure, but it is responsive to dissolved salts which depress the melting point. Thus, in winter, it is usual to salt sidewalks to keep water from freezing. 

Figure 8.10 Entropy of COi at a pressure of 0.1 MPa. At this pressure, the solid changes to gas at T= 194.52 K.

The enthalpy of formation of the substance that is obtained is for the gaseous state. The enthalpy that corresponds to the gas -> liquid change of state therefore needs to be added. The enthalpy corresponding to the liquid solid change is to be ignored if the enthalpy of formation of a substance in the solid state is required, since there is not much difference between the two. For the enthalpy of formation in the liquid state the enthalpy of condensation is calculated from the equation that bonds it to the entropic factor discussed in Chapter 1, ie ... 

The electronic properties of these oxygen-rich solids change drastically from that of the typically insulating ceramic La2Cu04. The material becomes first a metal and then a superconductor (Section 8.5). 

How does composition variation change the electronic properties of a solid Why does the electronic conductivity of a nonstoichiometric solid change as the surrounding partial pressure changes ... 

The normal state of affairs during a diffusion experiment is one in which the concentration at any point in the solid changes over time. This situation is called non-steady-state diffusion, and diffusion coefficients are found by solving the diffusion equation [Eq. (S5.2)] ... 

The mixture is heated cautiously on a hot plate to avoid excess frothing. When the frothing has almost subsided, additional concentrated nitric add is added, 90 g. (65 ml., 1.0 mole) at a time, with swirling and intermittent heating to control the vigorous reaction. The solid changes from gray-black to a cream color after six 90-g. portions of concentrated nitric acid have been used. 

Melting Point The temperature at which a solid changes to a liquid. A melting range may be given for mixtures. 

Investigators have used the words carbon and soot to describe a wide variety of carbonaceous solid materials, many of which contain appreciable amounts of hydrogen as well as other elements and compounds that may have been present in the original hydrocarbon fuel. The properties of the solids change markedly with the conditions of formation and, indeed, several quite well-defined varieties of solid carbon may be distinguished. One of the most obvious and important differences depends on how the carbon is formed carbon may be formed by a homogeneous vapor-phase reaction it may be deposited on a solid surface that is present in or near the reaction zone or it may be generated by a liquid-phase pyrolysis. 

When thioamides 24f-h were irradiated in benzene with a high-pressure mercury lamp, iV-isopropyl-P-thiolactam 26 and 1,3,5-dithiazine 28 were obtained (Scheme 15 and Table 10, entries 1,3, and 5). Considerably different photochemical behavior was observed between that in solution and in the solid state. Powdered thioamide 24f was irradiated in the solid state at 0 °C until 19% conversion, because the solid changed to amorphous at around 20% conversion. In this case, only dithiazine 28f was obtained as the sole photoproduct (entry 2). On the contrary, photolysis of 24g gave a new type of p-lactam 27g as a main product in 88% yield in addition to dithiazine 28g (12%) the P-lactam 26g was not detected at all (entry 4). Photochemical ( ,Z) isomerization of (Z)-24g was also observed in the early stage of the reaction, where the ratio of the photostationary state was ZIE=1.9. In the case of 24h, P-thiolactam 27h was ob-... 

The surface property of a solid changes even after one layer of lipid is formed as an LB film, such as, the contact angle decreases after LB deposition. Similarly, many other physical methods have shown that LB films change the surface characteristics (Gaines, 1966 Adamson and Gast, 1997 Birdi, 2002a). 

The most common examples of fluid-solid reactions in which the size of solid changes are the reactions of carbonaceous materials such as coal briquettes, wood, etc. with low ash content to produce heat or heating fuels. For example, with an insufficient amount of air, producer gas is formed by the reactions... 

Other examples of reactions in which solids change in size are as follows. 

Freezing point is the temperature at which, a liquid or solution solidifies. It is the temperature at which the liquid and solid states of a substance are in equilibrium at a given pressure (usually atmospheric). The second definition may be applied to Melting (or Freezing) Point, which may also be defined as the temperature at which a solid changes to a liquid. For pure crystalline substances, mp is usually identical with ft p, while for many mixtures, they are not identical. For example, fats and waxes do not solidify until they have been cooled several degrees below their, mp s. 

Glass transition (temperature), Tgi The temperature at which the amorphous portion of a semicrysfalline solid changes from its glassy state, becoming soft and flexible (rubbery) not to be confused wifh melting femperafure. 

It is also assumed that the composition of the grown crystal does not change in the cooling process. As is well known for the case of finite quantity of melt, the composition of melt (liquid) and solid change along the liquidus and solidus curves, respectively. 

Three grams of oxalic add 2-hydrate are dissolved in 30ml of an equivolume mixture of water and ethanoL The solution is cooled and 6g of aquopentamminechromium (III) nitrate (No. 112) are stirred in. The mixture is continually stirred for 5 minutes on the steam bath the orange solid changes to a reddish tint during this time. The prod-... 

The term liquid is commonly reserved for T < T,. and "dense gas" is used for T - T,. However, certain properties, such as the ability to dissolve solids, change rather abruptly at the critical density. In many respects, the dense gas resembles the low-temperature liquid nf the same density mare closely than it does Ihe dilute gas. 

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