The characteristic vapor pressure of each liquid increases, non-linearly, with temperature.
Vapor pressure is an expression that refers to a phenomenon observed in closed systems at a certain temperature. It consists of a pressure exerted by the gas phase (or vapor) in the liquid phase when the latter and the vapor manage to reach a dynamic equilibrium.
When investigating the characteristics, applications and scope of vapor pressure , its importance within sublimation is noted, a process that revolves around the direct passage of a substance in a solid state to the gas phase. Specialists in this topic indicate that, in general, any solid with estimable vapor pressure exposed to a specific temperature can sublimate into air.
On the other hand, it is interesting to know that data on mixtures of liquids are obtained through Raoult's law . It can be combined with Dalton's law (focused on partial pressures) in order to find out what is the total vapor pressure of ideal solutions whose components reached liquid-vapor equilibrium .
Vapor pressure characteristics
It is necessary to keep in mind that, at a given temperature, the vapor pressure values corresponding to liquids that have a similar profile depend on the molecular mass : the larger it is, the lower the vapor pressure .
Knowing in depth the Clausius-Clapeyron equation , meanwhile, we notice that the number of molecules that a liquid loses or gains influences the value of the vapor pressure , as also happens with the composition of the liquid substance during equilibrium. . The vapor pressure , as long as it is a liquid with some free surface, does not depend on how much vapor or liquid there is. Furthermore, its value decreases as the molecular mass increases.
When dealing with a substance in the liquid phase, the vapor pressure is measured with an instrument called an isoteniscope .
Regardless of which substance is analyzed, it will also be possible to establish that the vapor pressure increases with temperature in a non-linear manner. We speak of boiling point , to add more precision, to identify the temperature at which the vapor pressure of the liquid is equal to the pressure that surrounds it and turns into vapor.
When, slowly and progressively, there is a change of state from liquid to gaseous, a process known as evaporation takes place. In cases in which the vapor pressure is equal to the atmospheric pressure , then the phenomenon called boiling is triggered.
The relative humidity of a system is determined based on the link, at a specific temperature, between the vapor pressure associated with water equilibrium and the partial pressure of water vapor.
Importance
Educating yourself about the theoretical definition and practical application of vapor pressure is useful given the wide and diverse scope of this pressure class. It is also necessary to know what precautions to take against substances with high vapor pressures and not ignore the risks associated with them. In this regard, it is worth highlighting that the higher the vapor pressure in a given liquid subjected to a specific temperature, the lower its boiling point and the greater its volatility .
In order to make the conservation and transfer of crude oil safer, for example, the reduction of its vapor pressure is used through partial distillation that aims to stabilize the oil .
Within Environmental Law, importance is given to vapor pressure since it is analyzed in relation to the maximum permitted concentration (CMP) of a substance to establish the hazard index and thus define whether said material is, or not, viable in certain conditions. scenarios or activities due to their level of volatility.
In the fields of chemical engineering and meteorology (a science in which atmospheric pressure , dew point and relative humidity are studied, among other issues), to add other references, practical applications of atmospheric pressure are also observed. steam .
Condensation occurs (a phenomenon that causes water to change to a liquid phase from a gaseous state) whenever the water vapor pressure exceeds the saturation vapor pressure.
Examples of vapor pressure
Once the theoretical foundations of vapor pressure are known, information linked to measurement methods is accumulated, factors that influence vapor pressure are identified and fields of application are distinguished, it is constructive to complement these data with specific examples. .
There are numerous elements and chemical compounds that have particularities linked to vapor pressure . Neon , specifically, is characterized by presenting, at a very low temperature, a high level of vapor pressure .
In the case of water , its physical properties are affected by solutes present in said vital substance. Among the alterations evident, one appears that conditions the relationship established between the vapor pressure of pure water and that associated with the solution.
A vapor pressure that, considering a temperature of 25 ºC, does not exceed 1 bar characterizes a saturated solution based on ammonium nitrate , while benzene stands out for showing a higher pure vapor pressure compared to that of toluene .