vapour pressure ppt

2

RANA MUDASSAR HAZOOR

MOAZAM YASEEN BAJWA

IRFAN KHAN

FAISAL REHM

AN

DATE 20/10/10

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R/N* 07

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OBJECTIVES…..

Vapours & GasVapour pressure and its different terminologiesFactors affecting the vapour pressureROULTS LAWVapour pressure loweringRelation b/w vapour pressure & temperature& boiling pointVapour pressure measurement methodsSlandered values of vapour pressure of different organic & inorganic compoundsApplications and uses of vapour pressureAnd many more…………………………

To understand

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Vapour

• A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point .

• This means that the vapor can be condensed to a liquid or to a solid by increasing its pressure without reducing the temperature.

• Vapor refers to a gas phase at a temperature where the same substance can also exist in the liquid or solid state, below the critical temperature of the substance

• water has a critical temperature of 374°C (or 647 K), which is the highest temperature at which liquid water can exist.

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Difference between gas and vapours

• gases for which no liquid or solid can form at the temperature of the gas– Gas is the phase

where no condensation occur

• Vapour is the phase which directly attached with liquid or solid– Vapour phase which

condense

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Vapor pressure

• Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. The pressure exerted by the gas in equilibrium with a solid or liquid in a closed container at a given temperature is called the vapor pressure. The gas that is above the liquid is called its vapor and it creates a pressure called vapor pressure

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VAPOUR PRE..CONT…

• The equilibrium vapor pressure is an indication of a liquid's evaporation rate

• A substance with a high vapor pressure at normal temperatures is often referred to as volatile

• All liquids and solids have vapor pressure at all temperatures except at absolute zero, -459°F (-273°C)

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Saturated Vapor Pressure

• The process of evaporation in a closed container will proceed until there are as many molecules returning to the liquid as there are escaping. At this point the vapor is said to be saturated, and the pressure of that vapor (usually expressed in mmHg) is called the saturated vapor pressure

• The saturated vapour pressure is the maximum pressure the vapour from a liquid (or solid/solution) can exert at a given temperature if the substance alone occupied a container in which the liquid/solution/solid is in equilibrium with the vapour

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Partial vapor pressure

• The vapor pressure that a single component in a mixture contributes to the total pressure in the system is called partial vapor pressure.

• For example, air at sea level, saturated with water vapor at 20 °C has a partial pressures of 24 mbar of water, and about 780 mbar of nitrogen, 210 mbar of oxygen and 9 mbar of argon.

12

Measurement and units

• Vapor pressure is measured in the standard units of pressure. The International System of Units (SI) recognizes pressure as a derived unit with the dimension of force per area and designates the pascal (Pa) as its standard unit. One pascal is one newton per square meter (N·m−2 or kg·m−1·s−2).

• Other units are psi , atm , bar , torr , mmHg.

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The Microscopic View• When a solid or a liquid evaporates to a gas in a

closed container, the molecules cannot escape.• Some of the gas molecules will eventually strike the

condensed phase and condense back into it.• When the rate of condensation of the gas becomes

equal to the rate of evaporation of the liquid or solid, the amount of gas, liquid and/or solid no longer changes.

• The gas in the container is in equilibrium with the liquid or solid.

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Microscopic equilibrium between gas and liquid. Note that the rate of evaporation of the liquid is equal to the rate of condensation of the gas

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How do molecules of the liquid become molecules of gas?

• Each molecule in the liquid has energy, but not the same amount. The energy is distributed according to the Maxwell-Boltzmann distribution. The Maxwell–Boltzmann distribution for the speed follows immediately from the distribution of the velocity vector, above. Note that the speed is

• Even if you don't know what that is, the point is that some molecules have a fairly large amount of energy compared to the average. Those are the ones we are interested in.

. .

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R/N*11

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Factors That Affect Vapor Pressure

Surface Area: the surface area of the solid or liquid in contact with the gas has no effect on the vapor pressure.

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FACTORS…CONT…

Types of Molecules:• the types of molecules that make up a solid or liquid

determine its vapor pressure. If the intermolecular forces between molecules are:

– relatively strong, the vapor pressure will be relatively low.

– relatively weak, the vapor pressure will be relatively high

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FACTORS…CONTEthyl ether (C4H10O):

Pvapor (25oC) = 520 torrThe relatively weak dipole-dipole forces and London dispersion forces between molecules results in a much

higher vapor pressure compared to ethyl alcohol.

Ethyl alcohol (C2H6O): Pvapor (25oC) = 75 torr

Although dipole-dipole forces and London dispersion forces also exist between ethyl alcohol molecules, the strong hydrogen bonding interactions are responsible for the much lower vapor pressure compared to ethyl ether.

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FACTORS…CONT Temperature: at a higher temperature, more molecules

have enough energy to escape from the liquid or solid. At a lower temperature, fewer molecules have sufficient energy to escape from the liquid or solid.

Microscopic equilibrium between gas and liquid at low temperature. Note the small number of particles in the gas.

Microscopic equilibrium between gas and liquid at high temperature. Note the large number of particles in the gas.

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if you were to put more liquid in, the vapor pressure would go up?

• there are two opposing processes at work:

(1) molecules leaving the liquid's surface .

(2) molecules returning to the liquid at its surface. • If we pour down some more liquid in already present

liquid the molecules leaving the surface and returning remain equal………..so no effect..

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Vapour pressure of mixtures

ROULTS LAW:• Raoult's law gives an approximation to the vapor

pressure of mixtures of liquids. It states that the activity (pressure or fugacity) of a single-phase mixture is equal to the mole-fraction-weighted sum of the components' vapor pressures

where p is vapor pressure, i is a component index, and χ is a mole fraction. The term piχi is the partial pressure of component i in the mixture.

• Raoult's Law is applicable only to non-electrolytes (uncharged species); it is most appropriate for non-polar molecules with only weak intermolecular attractions (such as London forces).

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Vapor Pressure Lowering

The Macroscopic View:• When a solute is added to a solvent, the

vapor pressure of the solvent (above the resulting solution) is lower than the vapor pressure above the pure solvent.

• The vapor pressure of the solvent above a solution changes as the concentration of the solute in the solution changes.

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V P LOWERING CONT…

• Non-Volatile Solutes• Experimentally, we know

that the vapor pressure of the solvent above a solution containing a non-volatile solute (i.e., a solute that does not have a vapor pressure of its own) is directly proportional to the mole fraction of solvent in the solution. This behavior is summed up in Raoult's Law:

Psolvent = Xsolvent Psolvent

Pure water - microscopic view.

1.0 M NaCl solution

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Volatile Solutes• A volatile solute (i.e., a solute that

has a vapor pressure of its own) will contribute to the vapor pressure above a solution in which it is dissolved. The vapor pressure above a solution containing a volatile solute (or solutes) is equal to the sum of the vapor pressures of the solvent and each of the volatile solutes.

Psolvent = Xsolvent Psolvent

Psolute = Xsolute Psolute

Psolution = Psolvent + Psolute

Pure liquid xenon

Krypton-xenon solution

27http://www.chem.purdue.edu/gchelp/liquids/vpress.html

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Relation between temperature and vapour pressure

• The vapour pressure of a substance increases non linearly with the increase in temperature. according to the Clausius–Clapeyron relation

TABLE 1. EQUILIBRIUM VAPOR PRESSURE OF WATER

TEMPERATURE °C

WATER VAPOR PRESSURE mm Hg

TEMPERATURE °C

WATER VAPOR PRESSURE mm Hg

0 4.6 60 149

10 9.2 70 237

20 17.5 80 355

30 31.8 90 526

40 55 100 760

http://science.jrank.org/pages/7148/Vapor-Pressure.html

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The vapor pressure of a liquid varies with its temperature, as the following graph shows for water. The line on the graph shows the boiling temperature

for water.

30http://www.chemteam.info/GasLaw/VaporPressure.html

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Boiling point

The boiling point of a substance is that temperature at which the vapor pressure equals to the applied pressure. At sea level or there about this isthe "normal boiling point" where the pressure is

1 atm = 760 mm Hg.

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Relation between boiling piont and vapour pressure

• The boiling temperature of water for atmospheric pressures can be approximated by Antoine equation:

• or transformed into this temperature-explicit form:

• where the temperature Tb is the boiling point in degrees Celsius and the pressure P is in Torr.

33FROM WIKIPEDIA FREE ENCYCLOPEDIA

Each compound starting from its boiling point

34WWW.DOCBROWN.INFO

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Altitude &boiling piont & vapour pressure

• The vapor pressure is a function of the temperature and the heat of vaporization, call it H, in the following way

• log [P2/P1] = -{ H/(2.303*1.987)} *[ 1/T2 - 1/T1]• The "log" is the common base 10 log, H is in cal/mol,

and T is in degrees K. • T1, P1 is the norma boiling point and atmosphere

pressure• T2, P2 is the boiling point and atmosphere pressure

at altitude

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Effect of Altitude

• The boiling point of a substance is that temperature at which the vapor pressure equals to the applied pressure. At sea level or there about this is the "normal boiling point" where the pressure is 1 atm = 760 mm Hg.

• The boiling point of a substance will depend upon the altitude, because the applied pressure is less and less, the higher the elevation.

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Cont….

31 in. Hg: 214 °F or 101.1 °C (at approx -1000 ft or -305 m below sea level)

30 in. Hg: 212.15 °F or 100 °C (at approx sea level)

29 in. Hg: 210.3 °F or 99.06 °C (at approx 1000 ft or 305 m above sea level)




Here are other values for the boiling point of water a various barometric pressures and the approximate altitudes that corresponds to under normal conditions

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vapor pressure: measurements

• Vapour pressure measurements based on following categories ,

– REID VAPOUR PRESSURE

– TRUE VAPOUR PRESSURE

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REID VAPOUR PRESSURE

• Reid vapor pressure (RVP), determined by the ASTM test method D323,56, is widely used in the petroleum industry to measure the volatility of petroleum crude oil, gasoline and other petroleum products. It is a quick and simple method of determining the vapor pressure at 37.8 °C (100 °F) of crude oil and petroleum products having an initial boiling point above 0 °C (32 °F).

• ASTM ..American Society for Testing and Materials under the designation ASTM D323-56

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Cont….

• RVP is the absolute pressures as distinguished from gauge pressures ,Because of the presence air (and its of water vapor content) in the vapor space within the test method's sample container, as well as some small amount of sample vaporization during the warming of the sample to 37.8 °C (100 °F), the RVP differs by a small amount from the TVP of

the sample.

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TRUE VAPOUR PRESSURE

• True vapor pressure (TVP), is a common measure of the volatility of petroleum distillate fuels. It is defined as the equilibrium partial pressure exerted by a volatile organic liquid as a function of temperature as determined by the test method ASTM D 2879.

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Sto

ck T

VP

psi

RV

P

psi

Sto

ck

Tem

p.

°F

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Sto

ck T

VP

psi

RV

P

psi S

tock

T

em

p.

°F

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R/N* 23

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METHODES TO MEASURE VAPOUR PRESSURE

Basically there are two ways to calculate the vapour pressure

• Theoretically measurement

• Experimentally measurement

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THEORETICAL MEASUREMENTS

The vapour pressure of a substance can be calculate theoretically by using different equations.

• Antoine equation

• Clausius-clapeyron equation

47

ANTOINE EQUATION

• Chemical engineers use antine equation to estimate the vapour pressure of pure liquid and solids.

• The results are more reliable than clausius-clapeyron equation.

• log P = A - B T + C

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• where A, B, and C are "Antoine coefficients" that vary from substance to substance.

• The Antoine equation is accurate to a few percent for most volatile substances (with vapor pressures over 10 Torr).

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name Range K A B C

Acitic acid 290-430 16.808 3405.75 -56.34

Benzene 280-377 15.9008 2788.51 -52.38

Ammonia 179-261 16.9481 2132.5 -32.98

Toluene 284-410 16.0137 3096.52 -53.67

Water 284-441 18.3036 3816.44 -46.13

N heptane 270-400 15.8737 2911.321 -56.51

N hexane 245-370 15.8367 2697.55 -48.78

N pentane 220-330 15.8333 2477.07 -39.94

Ethyl alcohol 270-369 18.5242 3578.91 -50.50

Cyclo hexane 280-380 15.7527 2766.63 -50.50

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CLAUSIUS-CLAPEYRON EQUATION

• Chemists often use the Clausius-Clapeyron equation to estimate the vapor pressures of pure liquids or solids

• ln (P/P°) =H/R (1/T° - 1/T)

H

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CONT….• where P is the vapor pressure, P° is

a vapor pressure at a known temperature T°, H is an enthalpy of vaporization R is the ideal gas law constant, and T is the temperature (in kelvins).

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CONT…..• Several of the assumptions fail at high pressure

and near the critical point, and under those conditions the Clausius-Clapeyron equation will give inaccurate results. Chemists still like to use the equation because it's good enough in most applications and because it's easy to derive and justify theoretically.

• Chemical engineers often use the more accurate Antoine equation to predict vapor pressures.

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Measurement of Vapor Pressure by a Static Method

In our laboratory two recently constructed static apparatuses are available. Static method allows measurement of vapor pressure in the liquid as well in the solid phases over a wide range of temperatures including room temperature. As the inner volume of the apparatuses is evacuated to pressure of about 10-5 Pa and the apparatus is regularly checked for tightness by a helium leak detector the static apparatuses allow measurement with compounds sensitive to oxygen and water. In the next two sections the apparatuses and their most recent improvements are described in some more details and the preparation of samples for vapor pressure measurement is discussed.

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• Apparatus for the vapor pressure measurement.

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Fig. 2 Apparatus STAT4 for the measurement of vapor pressure. Valve 1 is the container valve; valves

2 and 3 are computer controlled.Department of Physical Chemistry, Institute of Chemical Technology, 166 28

Prague 6, CzechRepublic

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REID VAPOUR PRESSURE method

• The reid vapour pressure is the absolute vapour pressure and the true vapour pressure is the partial vapour pressure.

• RVP is the absolute pressure exerted by a liquid at 100F

• The higher the value, the more voaltile the sample and more readily it will evaporates.

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TEST METHOD

• Reid vapor pressure of gasolines and other products having a vapor pressure below atmospheric pressure

• . The liquid chamber is filled with a liquid sample that has been pre-chilled to a temperature of 32 to 40 °F (0 to 4 °C) and then the liquid chamber is very quickly connected to the vapor chamber fitted with a pressure gauge

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CONT…..• Shaked the apparatus for minimum 5

minutes and note the reading of vapour pressure from gauge.

RESULTS

VP of diesel = 2.4 psi

VP of kerocene = 1.7 psi

VP of mixture = 2.1 psi

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Manometric methode

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Other test methods for certain petroleum products

• Test method ASTM D323,56 is not applicable for liquified petroleum gases (LPG). ASTM D1267 or D6897 should be used for LPG.

• ASTM D323 is also not applicable for gasolines containing oxygenated compounds other than methyl tertiary-butyl ether (MTBE).[4] For gasolines containing other oxygenated compounds, refer to ASTM D4953.

• The International Organization for Standardization (ISO) has a test method, ISO 3007:1999, that is the equivalent of the ASTM D323 test method. Many European countries use that standard or have their own standards which are generally the same is the ISO standard.

• The Japanese Industrial Standard JIS K2258 includes the equivalent of the ASTM D323 test method.

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R/N* 31

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Apllications and uses of vapour pressure

• Air pollution regulatory authorities mandate maximum gasoline vapor pressures in many areas so as to limit the evaporative emissions of smog-forming hydrocarbons from gasoline.

• In 1996, with the implementation of the CaRFG2 (California's Phase 2 Reformulated Gasoline ) regulations, the RVP standard was reduced to a flat limit of 7.0 psi.

• In 2004, the CaRFG3 regulations are implemented with a RVP flat limit of 6.9 psi when the evaporative emissions model element of the Predictive Model is used and a cap limit of 7.2 psi

• Vapor pressure is also important as an indirect measure of the evaporation tendency of volatile petroleum solvents.

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CO2 Applications:

• It is necessary to keep the CO2 in a liquid state, especially as it experiences the pressure drop through the inlet valve.

• care must still be taken to keep the inlet piping pressure loss to a minimum.

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Inlet Pressure and Temperature must be in the Liquid range indicated on theabove CO2 Vapor Pressure Chart to keep CO2 as a liquid.

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Cont….

• in oil refineries, while designing the storage tank for crude oil vapour pressure is considered in account .

• In pressure cookers the vopur presssure of water is increased thus temperature of water also increases and result food cooked fast.

• Vapour pressure is used to check the volatility of a substance. higher the vapour pressure higher its volatility and vice versa.

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STANDARD VALUES

• VP OF PETRO 6.5 Psi

• Vp of kerocene 5.2Psi

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SubstanceVapor

Pressure(SI units)

Vapor Pressure

(Bar);

Vapor Pressure(mmHg);

Temperature

Tungsten 100 Pa 0.001 0.75 3203 °C

Ethylene glycol 0.5 kPa 0.005 3.75 20 °C

Water (H2O) 2.3 kPa 0.023 17.5 20 °C

Propanol 2.4 kPa 0.024 18.0 20 °C

Ethanol 9 kPa 0.09 67.5 20 °C

Methyl isobutyl ketone

26.48 kPa 0.2648 198.62 25 °C

Freon 113 37.9 kPa 0.379 284 20 °C

Acetaldehyde 98.7 kPa 0.987 740 20 °C

Butane 220 kPa 2.2 1650 20 °C

Formaldehyde 435.7 kPa 4.357 3268 20 °C

Carbonyl sulfide 1.255 MPa 12.55 9412 25 °C

Propane 2.2 MPa 22 16500 55 °C

Oxygen (O2) 54.2 MPa 542 407936 20 °C

Nitrogen (N2) 63.2 MPa 632 475106 20 °CFROM WIKIPEDIA FREE ENCYCLOPEDIA

70

substance vapor pressure at 25oC

diethyl ether 0.7 atm

bromine 0.3 atm

ethyl alcohol 0.08 atm

water 0.03 atm

http://www.chem.purdue.edu/gchelp/liquids/vpress.html

71

The maximum differences between the pressures represented by the actual curves and the theoretical straight lines are roughly as follows: -

Methyl alcohol and water . . . . . . .43 mm Hg

Ethyl . . . . . . . . 112 ,,

n-Propyl . . . . . . . . . 203 „

Isobutyl . . . . . . . . . . . 315 „

http://chestofbooks.com/science/chemistry/Distillation-Principles-And-Processes/Vapour-Pressures-Of-Mixed-Liquids-Part-4.

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• Vapour pressure is the pressure of vapours on the surface of liquid

• It depends upon temperature, external pressure, altitude and intermolecular forces

• Its independent to surface area• The vapour pressure of mixtures is governed by Roults

law.• Its measures in two different categories

– Reid vapour pressure– True vapour presssure

73

Cont…..• We can measure vapour pressure

experimentally and theoretically– theoretically by Antoine equation– Experimentally by following methods

• Reid vapour pressure method• Manometer method• Static method

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References• From Wikipedia, the free encyclopedia• http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/vappre.html• http://www.chem.purdue.edu/gchelp/liquids/vpress.html• http://science.jrank.org/pages/7148/Vapor-Pressure.html• American Society for Testing and Materials (ASTM).

http://www.arb.ca.gov/fuels/gasoline/rvp/rvp.htm• http://www.chemteam.info/GasLaw/VaporPressure.html• WWW.CHEM.PURDUE.EDU• WWW.CHEMTEAM.EDU• Test method D323-08 of the American Society for Testing and

Materials (ASTM). ASTM website page• Béla G. Lipták (Editor) (2003). Instrument Engineers'

Handbook: Process Measurement and Analysis, 4th Edition. CRC Press. ISBN 0-8493-1083-0. See page 1595.

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Cont…• AP42, Chapter 7, Section 7.1 On pdf pages 54-56 of 123 pdf

pages. All units are U.S. customary units.• For more information about MTBE, see Gasoline.• Petroleum products and crude petroleum - Determination of

vapour pressure - Reid method ISO 3007:1999 from the website of the International Organization for Standardization (ISO)JIS K 2258:1998

• Retrieved from "http://en.citizendium.org/wiki/Reid_vapor_pressure"

• Categories: CZ Live | Chemistry Workgroup | Engineering Workgroup | Chemical Engineering Subgroup | All Content | Chemistry Content | Engineering Content | Chemical Engineering tag

• Hidden categories: Chemistry tag | Engineering tag• http://en.citizendium.org/wiki/Reid_vapor_pressure

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