In different circumstances, it can be the capacity to do work, or the capacity to provide heat or radiation. A positive pressure indicates that the system tends to expand whereas a negative pressure tends to contract.ĭensity of any substance is its mass (kg) divided by its volume (m 3).Įnergy is difficult to define precisely, being based on the Laws of thermodynamics. It may be positive or negative and is not, in itself, directional. Pressure is the force per unit area ( Pa). Several temperature scales have been described, but the SI scale uses the kelvin. It is a bulk property of matter (as are pressure, concentration, density, refractive index, and melting point) and should not be applied to single particles (e.g., molecules a single particle may possess energy but does not have a temperature).

Hotness is a body's ability to impart energy as heat to another colder body. Temperature is a quantitative measure of hot and cold ( K). Latent heat is the energy required to cause phase changes between liquids, gases, and solids. Sensible heat is the energy required to change the temperature of a substance with no phase change. Heat is the amount of energy flowing from one body of matter to another spontaneously due to their temperature difference or by any means other than through work or the transfer of matter. Biological systems (e.g., live people) are not in thermodynamic equilibrium as they are not static and are subject to the movement of matter and energy to and from other systems. Thermodynamics is not to be confused with kinetics, which describes the rate of change of processes and their mechanisms and depends on the pathway chosen. Thermodynamics describes the energy content of systems at equilibrium and their transformations and is independent of the pathway chosen. Remember this, and one will not be misled by purveyors of 'too good to be true' ideas such as running cars on just water.

Of great importance is that the laws of thermodynamics are fundamental laws of the Universe and cannot be circumvented. The list of property identifiers needed in the calling arguments and instructions are available in the Thermophysical Function help.This webpage forms an elementary introduction to the terms and ideas of thermodynamics. 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. However, all ideal gas substances (which have a chemical symbol name, e.g., N2, CO2, CH4) have enthalpy values corresponding to JANAF table references. 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.

Absolute third law entropy of mixture