gas “standard state”（273.15KThe0.101325MPa）The definition is not arbitrarily set, but based onScientific principles, historical practice, and industry universalityThe core goal of the consensus formed is to establish a unified, easily reproducible, and natural standard for gas volume measurement. The determination of this standard can be based onFundamentals of Thermodynamics, Historical Inheritance, PracticalityBreaking down the three core dimensions:

1、 Fundamentals of Thermodynamics: Anchoring The baseline state of molecular motion

The essence of gas volume is the space of molecular motion——Temperature determines the intensity of molecular motion (the higher the temperature, the larger the intermolecular distance, and the volume expands), while pressure determines the degree to which molecules are compressed (the higher the pressure, the smaller the intermolecular distance, and the smaller the volume). To standardize volume measurement, one must choose oneMolecular motion states are stable and easily defined by physical lawsThe temperature and pressure benchmark, and273.15K（0℃）And0.101325MPa（1 The standard atmospheric pressure precisely meets this requirement.

1. Temperature 273.15K (0 ℃): Based on the "phase transition point of water", it is easy to reproduce and universal

273.15KyesThermodynamic temperature scale(Kelvin temperature scale) Chinese“Equilibrium temperature of ice water mixture”Corresponding to the Celsius temperature scale0℃——This temperature is the most easily reproducible in nature“Fixed temperature point”one of:

·Water is a globally distributed and stable substance The temperature of the "solid (ice) - liquid (water) equilibrium state" is not affected by geographical location or equipment accuracy (at 1 standard atmospheric pressure, the temperature of the ice water mixture remains constant at 0 ℃);

·When early scientists studied the properties of gases (such as Boyle's law and Charles' law), they often used Using "0 ℃" as the reference temperature, it was found that the "volume temperature pressure relationship" of the gas is most concise at this time (for example, the ideal gas state equation has the smallest calculation error at 0 ℃);

·Subsequent thermodynamic temperature scales will0K (absolute zero, where molecules stop moving) is set as the starting point, and the temperature difference between 0 ℃ (ice water mixture) and absolute zero is exactly 273.15K. This value becomes a key bridge connecting the Celsius temperature scale and the thermodynamic temperature scale, and is naturally included in the definition of standard conditions.

2. Pressure 0.101325MPa (1 standard atmospheric pressure): Based on the "Earth's average atmospheric environment", close to practical applications

0.101325MPaequal to1 standard atmospheric pressure（1atm）Its definition originates from“Average atmospheric pressure near sea level”：

·Early industrial and scientific research were mostly focused on Under "normal pressure environment" (such as laboratories, factory workshops), sea level atmospheric pressure is a common "natural pressure benchmark" that can be reproduced without additional pressure or pressure reduction;

·The value of standard atmospheric pressure (101325 pascals) is determined through precise measurement: at sea level at latitude 45 ° and 0 ℃, the atmospheric pressure per unit area is approximately 1.033 kg/cm ², which is equivalent to 0.101325 MPa in the International System of Units;

·Choosing this pressure can increase the standard volume 'Close to actual usage scenarios' - for example, the storage, transportation, and use of gases such as air and natural gas are mostly carried out under conditions close to atmospheric pressure, with smaller conversion errors between standard and actual conditions.

Summary: The definition of standard condition is The unity of "scientific laws+historical practice+industry demand"

273.15K（0℃）The choice is based on the fact that the phase transition point of water is easy to reproduce and highly consistent with the thermodynamic temperature scale;0.101325MPa（1 The selection of standard atmospheric pressure is based on the universality of the Earth's natural environment and is close to most industrial conditions. This combination not only enables gas volume measurement“universal language”This ensures the accuracy, comparability, and practicality of the data, ultimately becoming the standard for the global industrial and scientific communities.