![]() ![]() ![]() The list of property identifiers needed in the calling arguments and instructions are available in the Thermophysical Function help. Standard entropy values are indicated as S and are for substances at 1 bar pressure and 1 molal solution concentration. The JANAF table reference for entropy is based on the Third Law of Thermodynamics which references the entropy of all pure crystalline substances to zero at absolute zero temperature. Qualitatively, entropy is simply a measure how much the energy of atoms and molecules become more spread out in a process and can be defined in terms of statistical probabilities of a system or in terms of the other thermodynamic quantities. Unlike P, V, and T, which are quite easy to measure, the entropy of a system is difficult to calculate. A container of ideal gas has an entropy value, just as it has a pressure, a volume, and a temperature. The symbol for entropy is S, and the units are J/K. However, all ideal gas substances (which have a chemical symbol name, e.g., N2, CO2, CH4) have enthalpy values corresponding to JANAF table references. Entropy is a state function that is often erroneously referred to as the 'state of disorder' of a system. Entropy is in some sense a measure of disorder. The reference state upon which the value of enthalpy is based varies with the substance. Temperature must be the only argument, in addition to the substance name. The specific entropy of incompressible substances is a function of only temperature. Note also that for substance AirH2O (psychrometrics), the specific entropy returned by this function is the entropy of the air and water vapor mixture per unit mass of dry air. The remaining two can be any of the following: temperature (T), enthalpy (H), internal energy (U), relative humidity (R), humidity ratio (W), wetbulb (B), or dewpoint (D). One of these arguments must be total pressure (P). For all pure substances, the entropy function always requires two arguments, in addition to the substance name.įor AirH2O, three arguments are required. The value and units of the returned value depends on the Unit System setting. ENTROPY returns the specific entropy of a specified substance. ![]()
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