Comparing Solids, Liquids, and Gases

Why are liquids and solids so different from gases There are two reasons for this difference in behavior. 

Molecules are much closer to one another in liquids and solids, in the gas state, particles are typically separated by ten molecular diameters or more in liquids and solids, they touch one another. This explains why Hquids and soUds have densities so much larger than those of gases. At 100°C, 1 atm, water (H20(/)) has a density of 0.95 g/mL that of steam (H20(g)) under the same condition is only 0.00059 g/mL (Table 9.1). Because of such small numbers for gas densities, they are usually given in g/L, whereas those of liquids and solids are in g/mL. 

For the same reason, liquids and solids are much less compressible than gases. When the pressure on liquid water is increased from 1 to 2 atm, the volume decreases by about 0.0045%. The same change in pressure reduces the volume of an equal amount of ideal gas by 50%. 

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