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.

• Freezing Point Depression

  • The freezing point depression can also be explained in terms of vapor pressure.
  • Adding solute to a solvent will essentially dilute the solvent molecules, and according to Raoult's law, this leads to a decrease in vapor pressure.
  • Considering the fact that the vapor pressure of the solid and liquid forms must be the same at freezing point, because otherwise the system would not be at equilibrium, the lowering of the vapor pressure leads to the lowering of the temperature at which the vapor pressures of the liquid and frozen forms of the solution will be equal.
  • A triple phase diagram which shows the pressure and temperature of the normal boiling and freezing points of a solvent (green lines) and the boiling and freezing points of a solution (purple lines).
  • Notice that at 1 atm of pressure, the freezing point has been lowered (represented by numbers 2 and 4).

• 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.

• Three States of Matter

  • A gas at a temperature below its critical temperature can also be called a vapor.
  • A vapor can be liquefied through compression without cooling.
  • It can also exist in equilibrium with a liquid (or solid), in which case the gas pressure equals the vapor pressure of the liquid (or solid).
  • A supercritical fluid (SCF) is a gas whose temperature and pressure are greater than the critical temperature and critical pressure.
  • The video also discusses melting, vaporization, condensation, and freezing.

• Mercury

  • It is the only metal that is liquid at standard conditions for temperature and pressure.
  • Mercury even reacts with solid sulfur flakes, which are used in mercury spill kits to absorb mercury vapors.
  • Sodium amalgam is a common reducing agent in organic synthesis, and it is also used in high-pressure sodium lamps.
  • It is also used in lighting—electricity passed through mercury vapor in a phosphor tube produces short-wave ultraviolet light, causing the phosphor to fluoresce and produce visible light.
  • Mercury is a silvery metal that is liquid at standard temperature and pressure (STP).

• Earth's Atmosphere

  • By volume, air is made up of approximately 78% nitrogen, 21% oxygen, and 1% argon, with small amounts of additional gases including water vapor and carbon dioxide.
  • Carbon dioxide, water vapor, and other greenhouse gases are adept at stopping heat from leaving the atmosphere, causing the Earth to heat up.
  • Both air pressure and density increase upon approaching the Earth's surface.
  • The layer closest to the Earth, the troposphere, contains most of the water vapor and is where weather occurs.