Boiling is a phenomenon that is characteristic of any liquids. It manifests itself in the fact that vapor bubbles form throughout the solution. It should be noted that boiling is observed only at a certain temperature and depends on the type of substance. This indicator is an important characteristic. It can be used to separate liquid compounds, as well as to determine their purity.
This indicator is different in different substances. So, the boiling point of engine oil reaches 300-490 ° C, and for water it is 100 ° C. This
physical quantity depends on several parameters, including the conditions of boiling and the composition of the substance that is heated.
I must say that the boiling point has certain features. So, vapor pressure is created on the surface of the liquid, which forms rather slowly in the presence of a free surface. If we are talking about the middle of the medium, then it can be heated much more than during boiling. This explains the phenomenon of “overheating”, in which the liquid does not boil, but is characterized by
high temperature indicators.
It should be noted that the boiling point is determined using a special thermometer, which must be immersed in the vapor of the substance, and not in the liquid. At the same time, the mercury column is not always able to be completely loaded; therefore, the correction of the thermometer must be taken into account. For different liquids, this value is different. On average, it is believed that a change in atmospheric pressure of about 26 mm leads to the fact that the boiling point changes by one degree.
How does this indicator help determine the purity of mixtures and solutions? A homogeneous liquid is characterized by a constant boiling point. Its change is a sure sign of the presence of impurities that can be distinguished in the process of distillation, as well as using special devices - reflux condensers.
It is worth noting that in some cases, combinations of various substances are specially used. This gives the fluid specific features. For example, pure ethylene glycol boils at 197 ° C, and the boiling point of antifreeze is slightly lower - about 110 ° C.
The transition of liquid into steam occurs precisely when the corresponding boiling point is reached. In this case, saturated vapor above the surface of the liquid has the same numerical value with external pressure, which leads to the formation of bubbles throughout the volume.
I must say that boiling takes place at the same temperature, but with a decrease or increase in external pressure, one can observe its corresponding changes.
This can explain the phenomenon when food in the mountains takes longer to cook, because at a pressure of about 60 kPa, water boils even at 85 ° C. For the same reason, dishes in a pressure cooker cook much faster due to the fact that the pressure rises in it, and this leads to a concomitant increase in the temperature of the boiling liquid.
It should be noted that boiling is the most common way of physical disinfection. Without this process, it is impossible to cook any dish. It is also important for the distillation of petroleum products in order to obtain cleaner starting materials.