Heat content or enthalpy

Energy balances differ from mass balances in that the total mass is known but the total energy of a component is difficult to express. Consequently, the heat energy of a material is usually expressed relative to its standard state at a given temperature. For example, the heat content, or enthalpy, of steam is expressed relative to liquid water at 273 K (0°C) at a pressure equal to its own vapor pressure. 

In examining the tower performance it is not the air temperature that sets the capacity, but the heat content or enthalpy of the air. Although the air temperature and wet bulbs at inlet may be different for two different inlet air conditions, it is still possible for the air to have the same enthalpy. Therefore, two different air streams of different conditions can produce the same effect on totver performance. The heat content or enthalpy of all air with the same wet bulb is the same, therefore it is clear that the wet bulb temperature is important and sets the performance. 

ALL CHANGES IN PHASE involve a release or absorption of calories. One reason for this is that each solid has its own heat capacity. That is, there is a characteristic heat content for each material which depends upon the atoms composing the solid, the nature of the lattice vibrations within it, and its structure. The total heat content, or enthalpy, of each solid is defined by ... 

H is a measure of the heat content, or enthalpy, of a compound, and AH is preceded by a minus sign if the products have a lower heat content than the starting materials when there is such a decrease in enthalpy the reaction is exothermic. 

Qdiff = ASg - ASads where AHg and AHads are heat contents or enthalpies (see below)... 

Heat Content or Enthalpy. A thermodynamic property closely related to energy. It is defined by H = E + PV where E is the internal energy of the system, P is the pressure on the system and V is the volume of the system. Often it is used in differential form as in. AH = AE + PAV for a constant pressure process... 

The term specific heat refers to the sensible-heat content of either vapor or liquid. The specific heat is the amount of heat needed to raise the temperature on one pound of the vapor or liquid by 1°F. The term latent heat refers to the heat of vaporization, or the heat of condensation, needed to vaporize or condense one pound of liquid or vapor at constant temperature. Note that the heat of condensation is equal to the heat of vaporization. Each is referred to as the latent heat. The sum of the sensible heat, plus the latent heat, is called the total heat content, or enthalpy. 

Hessian functional determinant Hermite polynomial, heat content or enthalpy=P+PJ (quantity of heat) [magnetic field strength] Hamiltonian function, magnetic field strength. 

The heat of sorption is the difference in specific heat content or enthalpy between the bound moisture and that freely attached at the same temperature and total pressure. This enthalpy difference is normally derived from a form of the Clausius-Clapeyron equation on the assumption that the moisture vapor phase acts like an ideal gas and the molal volume of the condensed phase is negligible compared with that of the vapor. These considerations lead to the expression... 

If a solid sublimes, there will be a large increase in volume (AF), because the volume of a solid is negligible compared with that of its vapour, and work (PAV) has to be done against the applied pressure (P), in this case atmospheric pressure. The energy required to sublime the solid is therefore equal to the difference between the internal energies of vapour and solid plus the work done in expansion, and is expressed mathematically in Equation (1). AH is the heat content or enthalpy of the transition and is the same, in this example, as the latent heat of sublimation per mole. 

The constants a, b, c, and d are to be determined either experimentally or by some theoretical or semi-empirical approach. The heat content, or enthalpy (H), is determined from the heat capacity by a simple integration of the range of temperatures for which the formula for Cp is valid. Thus, if 298K is taken as a reference temperature. 

F is the free energy or free enthalpy H is the heat content or enthalpy... 

The term (U + PV) is called heat content or enthalpy, H, so that... 

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