vapor pressure

Examples of vapor pressure 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

• 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.

• Liquid to Gas Phase Transition

  • 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.
  • This is because the liquid can be heated less in order for its vapor pressure to equal the atmospheric pressure.
  • 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.

• 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.

• Humidity, Evaporation, and Boiling

  • The capacity of air to hold water vapor is based on vapor pressure of water.
  • Then equilibrium has been achieved, and the vapor pressure is equal to the partial pressure of water in the container.
  • 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.

• Solid to Gas Phase Transition

  • Also, at pressures below the triple point pressure, an increase in temperature will result in a solid being converted to gas without passing through the liquid region.
  • 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.

• Collecting Gases Over Water

  • The partial pressure of H2O is known as the vapor pressure of water and is dependent on the temperature.
  • To determine the quantity of gas we have collected alone, we must subtract the vapor pressure of water from the total vapor pressure of the mixture.
  • (At 295 K, the vapor pressure of water is 19.8 torr.)
  • If the water levels inside and outside the bottle are the same, then the total pressure inside the bottle equals 1.000 atm; at 25°C, the vapor pressure of water (or the pressure of water vapor in equilibrium with the liquid) is 23.8 mm Hg or 0.0313 atm.
  • When collecting oxygen gas and calculating its partial pressure by displacing water from an inverted bottle, the presence of water vapor in the collecting bottle must be accounted for; this is easily accomplished using Dalton's Law of Partial Pressures.

• Evaporation

  • With sufficient heat, however, the liquid would quickly turn into vapor.
  • Three key parts to evaporation are heat, atmospheric pressure (determines the percent humidity) and air movement .
  • Evaporation also tends to proceed more quickly with higher flow rates between the gaseous and liquid phases and in liquids with higher vapor pressure.
  • This vapor density and the partial pressure it creates are the saturation values.
  • They depend only on the vapor pressure of water.

• 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

• The Evaporating Atmosphere

  • Likewise, every once in a while a vapor molecule collides with the liquid surface and condenses into the liquid.
  • At room temperature and pressure, the water jar reaches equilibrium when the air over the water has a humidity of about 3%.
  • At 100 °C and atmospheric pressure, equilibrium is not reached until the air is 100% water.
  • The water vapor in it changes phases.
  • Collisions between water molecules in the atmosphere allows some to condense and some to remain in vapor.