partial pressure

(noun)

The pressure that one component of a mixture of gases contributes to the total pressure.

Related Terms

Examples of partial pressure in the following topics:

  • Dalton's Law of Partial Pressure

    • Dalton's Law of Partial Pressure states the total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of each individual gas.
    • Dalton's Law (also called Dalton's Law of Partial Pressures) states that the total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases.
    • where P1, P2 and Pn represent the partial pressures of each compound.
    • What is the partial pressure of He?
    • Our measurements demonstrate that the partial pressure of N2 as part of the gas PN2 is 0.763 atm, and the partial pressure of O2 as part of the gas PO2, is 0.215 atm.

  • Expressing the Equilibrium Constant of a Gas in Terms of Pressure

    • For gas-phase reactions, the equilibrium constant can be expressed in terms of partial pressures, and is given the designation KP.
    • For gas-specific reactions, however, we can also express the equilibrium constant in terms of the partial pressures of the gases involved.
    • Our equilibrium constant in terms of partial pressures, designated KP, is given as:
    • The reason we are allowed to write a K expression in terms of partial pressures for gases can be found by looking at the ideal gas law.
    • Write the equilibrium expression, KP, in terms of the partial pressures of a gas-phase reaction

  • Collecting Gases Over Water

    • The partial pressure of H2O is known as the vapor pressure of water and is dependent on the temperature.
    • The total pressure in the tube can be written using Dalton's Law of Partial Pressures:
    • Therefore, the partial pressure of oxygen gas is 1.000 - 0.031, or 0.969 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.
    • Apply Dalton's Law to determine the partial pressure of a gas collected over water.

  • The Rate Law

    • The rate law for a chemical reaction relates the reaction rate with the concentrations or partial pressures of the reactants.
    • The rate law for a chemical reaction is an equation that relates the reaction rate with the concentrations or partial pressures of the reactants.
    • The value of this coefficient k will vary with conditions that affect reaction rate, such as temperature, pressure, surface area, etc.
    • The rate of the reaction can be affected by the type of reaction as well as concentration, pressure, temperature and surface area.

  • Uses of Oxygen

    • Hyperbaric (high-pressure) medicine uses special oxygen chambers to increase the partial pressure of O2 around the patient and, when needed, the medical staff.
    • Oxygen gas is poisonous to the anaerobic bacteria that cause gas gangrene, so increasing its partial pressure helps kill them.
    • Increasing the pressure of O2 as soon as possible is part of the treatment.
    • A notable application of O2 as a low-pressure breathing gas is in modern space suits, which surround their occupant's body with pressurized air.
    • These devices use nearly pure oxygen at about one third normal pressure, resulting in a normal blood partial pressure of O2.

  • Liquid to Gas Phase Transition

    • If this is done with water, the partial pressure of water Pw in the space above the liquid will initially be zero (step 1).
    • 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.

  • Standard Free Energy Changes

    • The standard Gibbs Free Energy is calculated using the free energy of formation of each component of a reaction at standard pressure.
    • Pure liquids: the liquid under a total pressure of 1 atm.
    • Don't confuse these thermodynamic standard states with the "standard temperature and pressure" (STP) widely employed in gas law calculations.
    • Recall that the symbol ° refers to the standard state of a substance measured under the conditions of 1 atm pressure or an effective concentration of 1 Molar and a temperature of 298K.
    • As with standard heats of formation, the standard free energy of a substance represents the free energy change associated with the formation of the substance from the elements in their most stable forms as they exist under the standard conditions of 1 atm pressure and 298K.

  • Le Chatelier's Principle

    • A change in pressure or volume will result in an attempt to restore equilibrium by creating more or less moles of gas.
    • Similarly, if the volume of a system increases, or the pressure decreases, the production of additional moles of gas will be favored.
    • When the volume of the system is changed, the partial pressures of the gases change.
    • The system tries to counteract the decrease in partial pressure of gas molecules by shifting to the side that exerts greater pressure.
    • Similarly, if we were to increase pressure by decreasing volume, the equilibrium would shift to the right, counteracting the pressure increase by shifting to the side with fewer moles of gas that exert less pressure.

  • Solubility and Pressure

    • Increasing pressure will increase the solubility of a gas in a solvent.
    • Typically, a gas will increase in solubility with an increase in pressure.
    • In this equation, C is the concentration of the gas in solution, which is a measure of its solubility, k is a proportionality constant that has been experimentally determined, and Pgas is the partial pressure of the gas above the solution.
    • Henry's law does not apply to gases at extremely high pressures.
    • To prevent the bends, a diver must return to the surface slowly, so that the gases will adjust to the partial decrease in pressure and diffuse more slowly.

  • The Effect of Intermolecular Forces

    • At high pressures and low temperatures, intermolecular forces between gas particles can cause significant deviation from ideal behavior.
    • The Ideal Gas Law is a convenient approximation for predicting the behavior of gases at low pressures and high temperatures.
    • More electrons means that when two gas molecules collide or converge, the electron clouds around each nucleus can repel one another, thereby creating an "instantaneous dipole" (a separation of charge resulting in a partial positive and partial negative charge across the molecule).
    • At high pressures and low temperatures, these attractive forces can become significant.
    • By adding the term n2a/V2 to pressure, van der Waals corrected for the slight reduction in pressure due to the interaction between gas particles: