Text 18 В - раздел Образование, Part One THE PREDICATE Прочтите Текст Про Себя (Контрольное Время Чтения — 3 Минуты). The Nature Of ...
Прочтите текст про себя (контрольное время чтения — 3 минуты). The Nature of a Gas
That the molcculcs of a gas arc not held together, but arc moving freely in a volume rather large compared with the volumes of the molcculcs themselves is the characteristic feature of a gas. The Van dcr Waals attractive forces between the molcculcs still operate whenever two molcculcs come close together, but usually these forces arc negligibly small because the molcculcs are far apart. Because of this freedom of molecular motion, a specimen of a gas docs not have either definite shape or definite size. A gas shapes itself to its container.
Gases at ordinary pressure arc very dilute: the molcculcs themselves constitute only about one-thousandth of the total volume of the gas, the rest being empty space. Thus, I g of solid iodine has a volume of about 0.2 cm* (its density is 4.93 g/cm3), whereas 1 g of iodine gas at 1-atm pressure and at the temperature of I84°C (its boiling point) has a volume of 148 cm', over 700 times greater. The volume of all the molcculcs in a gas at ordinary pressure is accordingly small compared with the volume of the gas itself. On the other hand, the diameter of a gas molcculc is not extremely small compared with the distance between molcculcs; in a gas at room temperature and 1-atm pressure the average distance from a molcculc to its nearest neighbours is about ten times its molecular diameter.
