Liquids and Solutions
Text 26 A Liquids and Solutions - раздел Образование, Part One THE PREDICATE Solids And Gases Represent The Extreme States Of Behaviour Of Molcculcs. The ...
Solids and gases represent the extreme states of behaviour of molcculcs. The liquid state can be thought of as an intermediate condition in which some of the properties found in cither solids or gases arc displayed. Liquids, like gases arc isotropic and flow readily under applied stress, but like solids, they arc dense, relatively incompressible, and have properties that arc largely determined by the nature and strength of intcrmolecular forces. With respect to molecular order, liquids arc substances considered to be intermediate between solids and gases. The fact that liquids arc isotropic tells us immediately that they do not have the extended latticc structure and long-range order of solids. Yet, the density of a liquid is generally only 10% less than that of its solid phase; this must mean that the molecules in a liquid are packcd together with some regularity, and do not exhibit the complete chaos associated with molcculcs in the gas phase.
One of the most important properties of liquids is their ability of acting as solvents. In the first place, liquid solutions provide an extremely convenient means of bringing together carcfully measured amounts of reagents and of allowing them to react in a controlled manner. Second, the nature of the reactions which proceed and the speed at which they occur can be greatly influenced by the properties of the liquid solvent medium. Finally, the physical properties of solutions arc interesting and important, because they can be used to determine molecular weights of dissolved substances and to study the nature and strength of forccs between solvent and solute molcculcs.
One of the most engaging and absorbing features of the study of chcmistry is the attempt to explain the behaviour of bulk matter in terms of molecular properties. Therefore, it is important to outline a molecular picture which will help us to understand and relate phenomena associated with the liquid state.
