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## Properties of Gases ### Low Density The density of a gaseous substance at atmospheric pressure is about 1/1000 the density of the same substance in the liquid or solid state. The reason is that the particles are so much farther apart in the gaseous state (assumption 1). ### Compressibility D...

## Properties of Gases ### Low Density The density of a gaseous substance at atmospheric pressure is about 1/1000 the density of the same substance in the liquid or solid state. The reason is that the particles are so much farther apart in the gaseous state (assumption 1). ### Compressibility During compression, the gas particles, which are initially very far apart (assumption 1), are crowded closer together. The volume of a given sample of a gas can be greatly decreased. Steel cylinders containing gases under pressure are widely used in industry. When they are full, such cylinders may contain more than 100 times as many particles of gas as nonpressurized containers of the same size could contain. ### Diffusion and Effusion Gases spread out and mix with one another, even without being stirred. If the stopper is removed from a container of ammonia in a room, ammonia gas will mix uniformly with the air and spread throughout the room. The random and continuous motion of the ammonia molecules (assumption 3) carries them throughout the available space. Such spontaneous mixing of the particles of two substances caused by their random motion is called diffusion. Gases diffuse readily into one another and mix together due to the rapid motion of the molecules and the empty space between the molecules. The gas molecules in each of the two flasks in Figure 1.2a continuously move about in separate flasks because the stopcock is closed. When the stopcock is open, the gas molecules continuously diffuse back and forth from one flask to the other through the opening in the stopcock, as shown in Figure 1.2b. Diffusion is a process by which particles of a gas spread out spontaneously and mix with other gases. In contrast, effusion is a process by which gas particles pass through a tiny opening into a vacuum.