Vaporization

Examples of Vaporization in the following topics:

• Vapor Pressure of Nonelectrolyte Solutions

  • When a solute is added to a solvent, the vapor pressure decreases.
  • The decrease in entropy difference lowers the vapor pressure.
  • Raoult's law states that the vapor pressure of an ideal solution is dependent on the vapor pressure of the pure solvent and the mole fraction of the component present in the solution.
  • For an ideal solution, equilibrium vapor pressure is given by Raoult's law:
  • Calculate the vapor pressure of a nonelectrolyte solution using Raoult's law

• Liquid to Gas Phase Transition

  • There are two types of vaporization: evaporation and boiling.
  • Pvap is known as the "equilibrium vapor pressure", or simply as the "vapor pressure" of the liquid.
  • The variation of vapor pressure with temperature is not linear.
  • If the vapor pressure of the drop is greater than the partial pressure of vapor in the gas phase, the drop will evaporate.
  • The variation of vapor pressure with temperature is not linear.

• Vapor Pressure of Electrolyte Solutions

  • The vapor pressure of an electrolytic solution is dependent on the ratio of solute to solvent molecules in a solution.
  • Vapor pressure is the pressure exerted by a vapor in equilibrium with its condensed phase, either liquid or solid, at a particular temperature.
  • Vapor pressure of a liquid is a colligative property.
  • To better visualize the effect of solute on the vapor pressure of a solution, consider a pure solvent.
  • This pure solvent has a certain vapor pressure associated with it.

• Water’s Heat of Vaporization

  • As a result of the network of hydrogen bonding present between water molecules, a high input of energy is required to transform one gram of liquid water into water vapor, an energy requirement called the heat of vaporization.
  • Water has a heat of vaporization value of 40.65 kJ/mol.
  • This vapor density and the partial pressure it creates are the saturation values.
  • They depend only on the vapor pressure of water.
  • Explain how heat of vaporization is related to the boiling point of water

• Humidity, Evaporation, and Boiling

  • The amount of water vapor the air can hold depends on its temperature.
  • The capacity of air to hold water vapor is based on vapor pressure of water.
  • The vapor pressure of water at 100ºC is 1.01×105 Pa, or 1.00 atm.
  • (b) As the temperature rises, water vapor enters the bubble because its vapor pressure increases.
  • (c) At 100ºC, water vapor enters the bubble continuously because water's vapor pressure exceeds its partial pressure in the bubble, which must be less than 1.00 atm.

• Evaporation

  • Evaporation is a type of vaporization of a liquid that only occurs on the liquid's surface.
  • With sufficient heat, however, the liquid would quickly turn into vapor.
  • Evaporation of water occurs when the surface of the liquid is exposed, allowing molecules to escape and form water vapor; this vapor can then rise and form clouds.
  • This vapor density and the partial pressure it creates are the saturation values.
  • They depend only on the vapor pressure of water.

• Boiling Point Elevation

  • Boiling point elevation can be explained in terms of vapor pressure.
  • Vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature.
  • A liquid boils when its vapor pressure is equal to the air pressure.
  • A solvent's vapor pressure will lower when a solute is added.
  • When the vapor pressure of the liquid matches the atmospheric pressure, the liquid will boil.

• Latent Heat

  • Similarly, energy is needed to vaporize a liquid, because molecules in a liquid interact with each other via attractive forces.
  • Even more energy is required to vaporize water; it would take 2256 kJ to change 1 kg of liquid water at the normal boiling point (100ºC at atmospheric pressure) to steam (water vapor).
  • A phase change we have neglected to mention thus far is sublimation, the transition of solid directly into vapor.
  • The opposite case, where vapor transitions directly into a solid, is called deposition.
  • The system is constructed so that no vapor evaporates while ice warms to become liquid water, and so that, when vaporization occurs, the vapor remains in of the system.

• Solid to Gas Phase Transition

  • The solid has such high vapor pressures that heating leads to a substantial amount of direct vaporization even before the melting point is reached.
  • The enthalpy of sublimation (also called heat of sublimation) can be calculated as the sum of the enthalpy of fusion and the enthalpy of vaporization.
  • Even ice has a measurable vapor pressure near its freezing point, as evidenced by the tendency of snow to evaporate in cold dry weather.
  • There are other solids whose vapor pressure overtakes that of the liquid before melting can occur.

• The Evaporating Atmosphere

  • Likewise, every once in a while a vapor molecule collides with the liquid surface and condenses into the liquid.
  • The water vapor in it changes phases.
  • Collisions between water molecules in the atmosphere allows some to condense and some to remain in vapor.