Standard State definition of Standard State in the Free Online Encyclopedia.

standard state [′stan·dərd ′stāt]

(physics)

The stable and pure form of a substance at standard pressure and a specified temperature, usually 298 K (77°F).

Standard State

a conventionally adopted thermodynamic state for individual substances and components of solutions. The concept of standard states was introduced in connection with the inability of simple thermodynamic principles to describe the actual behavior of substances with precision when pressure c or concentration c serves as the quantitative characteristic. The thermodynamic equations for ideal gases and solutions can be applied to real systems if the fugacity f is used instead of the pressure p and the activity a is used instead of the concentration c. The values of a and f for all substances in the standard state serve as reference values.

The standard state of gas at each temperature is the hypothetical state of an ideal gas when f = p = 1 and the gas has the properties inherent in a real gas at an infinitely small pressure. For individual liquid and crystalline substances, the state at normal pressure is adopted as the standard state at each temperature. In the case of solutions, the state of the pure solvent is usually adopted as the standard state for the solvent; for the solute, the standard state is the solute’s state in an infinitely dilute solution, where a = c (with c usually the molar fraction or molarity). The changes in thermodynamic parameters, such as the Gibbs free energy and entropy, for a certain process calculated by using f or a are independent of the choice of standard state provided that the state is unchanging in this calculation for all initial and final states. The degree sign is added as a superscript to the symbols designating the properties of a substance (characteristics of a process) in the standard state; for example AH°_formation would be standard enthalpy of formation of a particular substance.

Standard state concepts are widely used in physical chemistry. In comparing thermodynamic functions and making thermo-chemical calculations, for example, on the basis of Hess’s law, all heat effects of reactions must be referred to identical conditions since they are temperature-dependent and, to a lesser degree, pressure-dependent; for reactions in solutions, the heat effects are dependent on concentration. In thermochemistry the state of a substance at 298.15°K and p = 1 atmosphere (760 mm Hg) is adopted as the standard state. It should be noted that it is not required that the substance actually exist in the standard state. For example, the heat of formation of gaseous H₂0 in the standard state may appear in calculations even though a similar state is thermodynamically impossible for water vapor at p = 1 atmosphere and 25°C.

REFERENCE

Karapet’iants, M. Kh. Khimicheskaia termodinamika, 3rd ed. Moscow, 1975.

M. KH. KARAPETIANTS

Mentioned in	?		References in periodicals archive	?		Encyclopedia browser	?		Full browser	?
No references found	A joint study by the institute of Education and the Institute of Fiscal Studies has concluded that intelligent youngsters from poor homes are failing to get into universities because of low standard state schools, rather than class bias. Degree of separation by Liverpool Echo (Liverpool, England) If the Legislature agrees, the change would allow utilities to use nuclear power and new coal-burning technology to meet whatever "green'' standard state lawmakers approve. Should Coal Be Considered A Clean Fuel? by Russell Ray / Tampa Tribune & WFLA In its movement, the Bichon Frise standard states that he should move freely as well as cautiously and without any effort, and when racing it should hold its head as well as neck in a straight manner. The Bichon Frise Know and Understand the Standard by Sandra A Dean / Pets and Animals community	standard plane Standard Potential standard preemphasis standard pressure standard project flood standard propagation standard railing standard rate turn Standard Reference Material standard refraction standard sand standard sand Ottawa sand standard schnauzer standard score standard screen HDTV standard seawater standard semantics standard shaft Standard Solution standard source standard source A standard source B standard source C standard special standard star Standard State standard station standard subroutine standard target Standard TCP/IP Port standard temperature and pressure standard terminal arrival route standard test-tone power Standard Time Standard Time in the Ussr standard tolerance standard ton standard trajectory standard visibility standard visual range standard volume standard waveguide Standard Weight of Agricultural Products Standard Widget Toolkit standard wiggler standard wire gauge standard wire rope Standard, Magnetic Standard-bearer standard-frequency signal standard-hour plan	Standard Small Computer Standard Small Launch Vehicle Standard Smoker Standard social science model Standard Software Requirements Contract Standard Software/Supply System standard solution standard solution standard solution standard solution standard source standard source A standard source B standard source C Standard South African English Standard Southern British English standard special Standard Special Provisions Standard Specific Gravity Standard Specification for Ship Repair and Alteration Committee Standard Specifications for Public Works Construction Standard Specifications for Road and Bridge Construction Standard Spectrum Resource Format Standard Spending Assessment Standard Spoken American English Standard Squirrel Cage Motor standard star Standard State Standard State Zoning Enabling Act Standard Statement Of Requirement standard station Standard Statistical Establishment List Standard Statistical Region Standard streams Standard Study Number Standard Sub-Gridding Standard Subject Classification Codes Standard Subject Identification Code standard subroutine Standard Supply Module Standard Supply Numbering System Standard Supply Service Standard Support and Environmental Impact Statement Standard Surface-To-Surface, Missile, Antiradiation Standard Surgical Blood Order standard surgical scissors standard surgical scissors standard surgical scissors Standard Survey Monument Standard Survivable Message Set Standard Swahili Standard Switch Panel Standard System Applications Standard System Information Production Factory

Mentioned in

References in periodicals archive

Encyclopedia browser

Full browser

No references found

A joint study by the institute of Education and the Institute of Fiscal Studies has concluded that intelligent youngsters from poor homes are failing to get into universities because of low standard state schools, rather than class bias.

Degree of separation by Liverpool Echo (Liverpool, England)

If the Legislature agrees, the change would allow utilities to use nuclear power and new coal-burning technology to meet whatever "green'' standard state lawmakers approve.

Should Coal Be Considered A Clean Fuel? by Russell Ray / Tampa Tribune & WFLA

In its movement, the Bichon Frise standard states that he should move freely as well as cautiously and without any effort, and when racing it should hold its head as well as neck in a straight manner.

The Bichon Frise Know and Understand the Standard by Sandra A Dean / Pets and Animals community

standard project flood

standard propagation

standard railing

standard rate turn

Standard Reference Material

standard refraction

standard sand