Boiling
The boiling is the formation of Bulle S during a violent change of a trade Liquide towards the state vapor. This phenomenon is a Vaporisation.
It occurs when the Steam pressure is higher than the Atmospheric pressure: the vapor bubbles formed at the bottom of the container become stable and can thus go back to surface.
The point of boiling
The the highest Temperature that a body can reach before evaporating, in gas form, freely, names the not boiling . This temperature is calculated with the Atmospheric pressure of 1 atmosphere (101.3 kPa).
It is possible to define in an equivalent way the point of boiling as being the temperature to which the Steam pressure of the liquid is of 1 atmosphere.
For water, the point of boiling is of 100°C. The change of state is subjected to a heat of vaporization (approximately to 2250 J/g for water equalizes).
The point of boiling of a pure Substance is defined by a couple of values in its Diagramme of phase: the boiling point and the pressure of boiling . In the diagram of the phases, this point is located on the line separating the gas phase from the liquid phase. It is thus characterized by the physical sizes Pression and Température at the time of the transition between the state Liquide and the state Gazeux from the pure substance in question.
The point of boiling thus meets the conditions under which there can be a transition from phase of the liquid state at the gas state of a pure substance, which one describes of boiling or evaporation. In addition, the point of boiling plays the opposite part of the dew point. In the case of the pure substance, these two points is confused. When one carries to boiling a mixture of pure substances, the behavior differs and one then observes a zone of boiling instead of only one point. If the transition from the liquid phase to the gas phase is done below the point of boiling, one speaks about evaporation.
In the tables of thermodynamics, the boiling points are given in the standard state, i.e. with 1013,25 hPa. This point of boiling is then called not of standard boiling , and the temperature standard boiling point . The " term; not ébullition" is often employed to indicate the standard boiling point in the current language, although it reduces the couple of values to only one value, which is an abuse language.
A current application of the interdependence between boiling point and pressure of boiling is the pressure-cooker. It is thanks to an increase in the pressure (usually about the bar) that one can make pass the boiling point of the water of 100°C to approximately 120°C. These two temperatures correspond well to boiling points. However, only the value of 100°C is a value taken in the standard state, and by there the standard temperature of boiling of water. This is why the confusion of the two denominations is unsuitable, at all natural and must be avoided.
Process of boiling
Below (respectively beyond) the point boiling, any contribution of heat to the liquid (resp. to gas) does not lead that with a rise in the Temperature. Introduced energy is thus converted into kinetic energy for particles. On the contrary, at the time of the transition from phase, the temperature remains constant, just as pressure. The totality of the thermal energy brought makes progress the change of state.
At the point of boiling, any contribution of additional energy led to the diminution of the interactions physicochemical between the particles: those pass in a gas state. Energy necessary to a mole of one species to pass in a gas state is called Enthalpie of vaporization, also called in the case of one pure substance energy of vaporization. It is only when the totality of the particles is in a gas state that the temperature of the system recovers to increase.
Water, the Hydrogen peroxide, or alkaline solutions (as a solution of Soda) without particles of dust nor gas bubbles are able to be high at temperatures exceeding the temperature of boiling in perfectly smooth containers without entering in boiling. The smallest disturbance, like the vibration generated by the action to mix, is able to generate an explosive separation of the phases liquid and vapor, indicated under the term of Overheating.
For this reason in practice, one adds to the liquids likely to enter in overheating of the Pumice whose presence makes it possible boiling to start and to avoid the explosion.
See the detailed articles: Evaporation, Energy of vaporization and Overheating
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