Standard State


Also found in: Wikipedia.

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

References in periodicals archive ?
All work will be accomplished in accordance with the following: *Scope of Work (SOW), dated May 10, 2016; *Procedures for Selecting Contractors and Specifications for Contractor Services including Customary State Contract Provisions, dated August 28, 2008, Revision December 29, 2008 *General Special Provisions dated November 22, 2011 *Attachment C: Standard State Provisions for Contracts and Grants dated September 1, 2015 *Standard State Provisions for Architect/Engineer Professional Service Agreements all of which are attached hereto etc.
BY DARRAGH MCDONAGH MORE than [euro]900million has been paid to social welfare claimants who did not qualify for assistance under standard State schemes in the past five years.
5-GHz, 400-ps-period timing capture across all input channels and up to 128-megasample memory depth, the 16850 Series instruments provide a standard state data rate of 700 Mb/s as well as an upgrade option to 1,400 Mb/s.
Rather, they conducted standard state tests for mold, air flow, and air filter upkeep.
Samples that were rested in ASW for 17-24 h and tested in ASW are described here as being in a standard state.
The school receives double the standard state funding per pupil, amounting to more than $8,000 a student.
The standard State Contract term will be from the date of execution for a period of up to two (2) years.
The district bought the former Payless store at 47th Street East and Avenue S last June, and officials plan to operate it as the Pueblo Learning Center, a school for students in fifth through eighth grade who perform poorly on standard state exams or are otherwise in danger of flunking.
All work will be accomplished in accordance with the following: Scope of Work (SOW), dated September 28, 2015; Procedures for Selecting Contractors and Specifications for Contractor Services document including Customary State Contract Provisions, dated August 28, 2008, Revised December 29, 2008; Standard State Provisions For Architect/Engineer Professional Service Agreements General Special Provisions dated November 22, 2011; and Revised Standard State Provisions for Contracts and Grants dated September 1, 2015 all of which are attached hereto.
All work will be accomplished in accordance with the following: Scope of Work (SOW), dated October 6, 2014; Procedures for Selecting Contractors and Specifications for Contractor Services document including Customary State Contract Provisions, dated August 28, 2008, Revised December 29, 2008; Standard State Provisions For Architect/Engineer Professional Service Agreements General Special Provisions dated November 22, 2011; and Revised Standard State Provisions for Contracts and Grants dated September 2, 2014 all of which are attached hereto.
Offering a solution for India's high fuel taxes, a senior official of the International Air Transport Association (IATA), has proposed that India can eliminate excise and customs duty, and use a standard State tax.
There should be a standard state construction and maintenance agency which controls all the schools, where the school district give the requirements they need and then let the professionals do their job.

Full browser ?