Volume change, latent heat

Cluusius-Clupeyron Eijliation. Derived from equation 1, the Clapeyron equation is a fundamental relationship between the latent heat accompanying a phase change and pressure—volume—temperature (PVT data for the system (1) ... 

The entropy change AS/ - and the volume change AV/ - are the changes which occur when a unit amount of a pure chemical species is transferred from phase I to phase v at constant temperature and pressure. Integration of Eq. (4-18) for this change yields the latent heat of phase transition ... 

In addition to volume changes the effect of temperature is also important. Thus the specific latent heat of vaporization of a chemical is the quantity of heat, expressed as kJ/kg, required to change unit mass of liquid to vapour with no associated change in temperature. This heat is absorbed on vaporization so tliat residual liquid or tlie sunoundings cool. Alternatively an equivalent amount of heat must be removed to bring about condensation. Thus the temperature above a liquefied gas is reduced as tlie liquid evaporates and tlie bulk liquid cools. There may be consequences for heat transfer media and the strength of construction materials at low temperatures. 

Le — latent heat of evaporation. v2 — Vi = Ar = volume change accompanying unit mass of phase transition at the pressure p. 

The specific volume curves intersect at a point where Ar = 0 the latent heat, on the contrary, changes only very slightly with the temperature, and its curve is either horizontal, or exhibits a maximum, falling off slightly at higher pressures, and probably approaching the p axis. Thus, when Ar = 0, L f has a considerable positive value, and when L/ = 0, Ar has (probably) a considerable negative value. 

Following this fxmdamental information on the fusion diagrams, we must know the densities of the igneous rocks and their magmas at all temperatures, with their changes of volume during solidification the textures and structiures produced by various conditions of solidification the latent heats concerned in fusion of the magma and in assimilation by it of other rocks and many other physico-chemical data. 

At particular critical points (Tq, Pc) on the phase diagram of a substance, two phases can be found in thermodynamic equilibrium. Therefore, upon application of a pressure or a temperature gradient, a transformation occurs from one phase into the other. This is a phase transition, in many aspects similar to a transformation implying the change of aggregation state. However, the extent of the changes in a solid to solid transformation is much smaller. For example, latent heat or latent volumes associated with the transformations are quite small, sometimes even difficult to detect. 

Ni(C2HgN2)3(N03)2 is quite different - the space group type and the lattice change at (ca. 106 K). The transition show discontinuity of the cell volume and, as expected, there is a latent heat of transition. Notably at the critical temperature the two phases are structurally different and therefore they are in equilibrium at that temperature. A minor hysteresis is observed. 

The physical properties, latent heat (hfg), specific volume change (vfg), and liquid specific heat capacity (Cf),-are, all required to evaluate the method. Liquid specific heat capacity can usually be measured quite easily. Data are required from the... 

The pf-relations of the six different forms of ammonium nitrate are illustrated diagrammatically in Eig. 85. M. Bellati and R. Romanese, and U. Behn measured the changes in volume at atm. press, at the four transition points. M. Bellati and R. Romanese have also measured the latent heats of the transformation... 

In second-order transitions, there is no latent heat, nor discontinuous changes in volume or entropy. 

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