Alternative vapour pressure equations are discussed and references for original temperature-vapour relationship to a theoretically derivable formula, the. The Clausius-Clapeyron equation allows us to estimate the vapor pressure at Estimate the heat of phase transition from the vapor pressures at two temperatures \(T_1\) and \(T_2\), then a simple relationship can be found. Vapor pressure or equilibrium vapor pressure is expression of the relation between the vapor pressure and the temperature of pure liquid or solid substances.
Vapor pressure or vapour pressure in British spelling or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases solid or liquid at a given temperature in a closed system.
Vapor pressure - Wikipedia
The equilibrium vapor pressure is an indication of a liquid's evaporation rate. It relates to the tendency of particles to escape from the liquid or a solid. A substance with a high vapor pressure at normal temperatures is often referred to as volatile. The pressure exhibited by vapor present above a liquid surface is known as vapor pressure.
As the temperature of a liquid increases, the kinetic energy of its molecules also increases. As the kinetic energy of the molecules increases, the number of molecules transitioning into a vapor also increases, thereby increasing the vapor pressure.
Clausius-Clapeyron Equation - Chemistry LibreTexts
The vapor pressure of any substance increases non-linearly with temperature according to the Clausius—Clapeyron relation. The atmospheric pressure boiling point of a liquid also known as the normal boiling point is the temperature at which the vapor pressure equals the ambient atmospheric pressure.
With any incremental increase in that temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form vapor bubbles inside the bulk of the substance. Skills to Develop To know how and why the vapor pressure of a liquid varies with temperature.
To understand that the equilibrium vapor pressure of a liquid depends on the temperature and the intermolecular forces present. To understand that the relationship between pressure, enthalpy of vaporization, and temperature is given by the Clausius-Clapeyron equation. Nearly all of us have heated a pan of water with the lid in place and shortly thereafter heard the sounds of the lid rattling and hot water spilling onto the stovetop. When a liquid is heated, its molecules obtain sufficient kinetic energy to overcome the forces holding them in the liquid and they escape into the gaseous phase.
By doing so, they generate a population of molecules in the vapor phase above the liquid that produces a pressure—the vapor pressure of the liquid.
In the situation we described, enough pressure was generated to move the lid, which allowed the vapor to escape. If the vapor is contained in a sealed vessel, however, such as an unvented flask, and the vapor pressure becomes too high, the flask will explode as many students have unfortunately discovered. In this section, we describe vapor pressure in more detail and explain how to quantitatively determine the vapor pressure of a liquid.
As for gases, increasing the temperature increases both the average kinetic energy of the particles in a liquid and the range of kinetic energy of the individual molecules. The fraction of molecules with a kinetic energy greater than this minimum value increases with increasing temperature. Just as with gases, increasing the temperature shifts the peak to a higher energy and broadens the curve.
Some molecules at the surface, however, will have sufficient kinetic energy to escape from the liquid and form a vapor, thus increasing the pressure inside the container. As the number of molecules in the vapor phase increases, the number of collisions between vapor-phase molecules and the surface will also increase.
Eventually, a steady state will be reached in which exactly as many molecules per unit time leave the surface of the liquid vaporize as collide with it condense. At this point, the pressure over the liquid stops increasing and remains constant at a particular value that is characteristic of the liquid at a given temperature.
The rate of evaporation depends only on the surface area of the liquid and is essentially constant.