Liquifying Air

The liquification of air is an interesting process since it's composition is mainly a mixture of two diatomic gases, 78% N₂ and 21% O₂. Daniel Schroeder gives an excellent description of this process. The illustration above is adapted from his summary of data from the National Research Council's International Critical Tables, Volume 3 and from the CRC Handbook (Ed. Lide). The initial oxygen concentration of the liquid has been revised to 51.4% based on more recent measurements.

空气的液化是一个有趣的过程，因为其主要成分是两种双原子气体的混合物，氮气占78%，氧气占21%。Daniel Schroeder对此过程有很好的描述。上图改编自他总结的来自加拿大国家研究委员会的《国际临界表》第三卷以及CRC手册（编者Lide）的数据。根据更近期的测量结果，液体中氧的浓度已修订为51.4%。

The liquification point of a mixture of gases with different boiling points will typically be between the boiling points of the pure gases. The boiling point of pure oxygen, O₂, is 90.6 K and the boiling point of nitrogen, N₂, is 77 K. If air is cooled at atmospheric pressure, it remains a gas until the temperature reaches 81.6 K, 9 K below the liquification temperature of pure oxygen. It will be completely liquified at about 79 K, 2K above the liquification point of pure nitrogen. Plunging an air-filled balloon into liquid nitrogen will lead to the liquification of almost all the air in the balloon. The liquid can be clearly seen inside the balloon.

混合气体的液化点通常位于其纯气体的沸点之间。纯氧O₂的沸点是90.6 K，氮气N₂的沸点是77 K。如果在大气压下冷却空气，它会保持气体状态，直到温度降至81.6 K，这比纯氧的液化温度低9 K。它将在约79 K时完全液化，这比纯氮的液化温度高2 K。将装有空气的气球浸入液氮中，会导致气球内几乎所有的空气被液化。液态物质可以在气球内清晰地看到。

Typical of the balloons used in a "shrinking balloon" demonstration is an air volume of about 6 liters or about one quarter of a mole. Using 29 grams as a mole of air and assuming a liquid density of 0.785 gm/cm³ leads to an estimate of almost 10 cm³ of liquid from such a balloon.

用于“缩小气球”演示的典型气球体积约为6升，或约四分之一摩尔。使用29克作为空气的摩尔质量，并假设液体密度为0.785克/立方厘米，可估算出此类气球约对应10立方厘米的液体。