raoult law

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Instituto Politécnico Nacional. Escuela Superior de Ingeniería Química e Industrias Extractivas. Laboratory phase equilibrium thermodynamics Professor : Miguel Sánchez Pasten Students : Alvarez Gómez Mauricio Alexis Gómez Vega Luz Yohaida Gruop: 2IV31 Team: 3

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Page 1: Raoult Law

Instituto Politécnico Nacional.

Escuela Superior de Ingeniería Química e Industrias Extractivas.

Laboratory phase equilibrium thermodynamicsProfessor : Miguel Sánchez Pasten

Students :Alvarez Gómez Mauricio Alexis

Gómez Vega Luz Yohaida

Gruop: 2IV31 Team: 3

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Raoult´s law

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Dew points refer to the temperature and pressure at which a condensed system . When, for example , in a room they begin to tarnish the glass case that has reached the point of saturation local moisture and temperature drop that moisture " rushes " , condensing on surfaces. Morning dew on the leaves of plants is a similar example

Bubble points , temperature and pressure in turn, refer to conditions under which a system is started boiling . In simply heating water, the time is the first bubble of steam formed , has reached bubble conditions.

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Vapor phase fits the behavior of an ideal gas , ie at low to moderate pressures the liquid phase is an ideal solution, provided they are similar chemical species that must be met : • The enthalpy of solution ( enthalpy of mixing ) is zero . • No change in volume in the mix • The vapor pressure of the solution is adjusted to Raoult's law . • activity coefficients for each component ( which is a measure of the deviation from ideality ) are equal to 1

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Expression of Raoult's Law PA = xA . A

Expression of the law of DaltonPT= PA + PB PA = yA . PT y PB = yB . PT

Xi being the mole fractions of the components in the liquid phase , yi mole fractions of components in the vapor phase Pi and the vapor pressures of the components. That is generally an ideal solution to have to : yi . PT = xi . i Application limitation : only one species whose applicable Vapor P is known , para This requires that species are in the subcritical range .

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Case study This system has a pressure of 90 kPa , comprising water and ethyl alcohol . The concentration of alcohol in the liquid mixture is 40 mol % , ie , about 1.705 grams of alcohol per gram of water present . We wish to determine the temperature at which the solution , considering it as ideal, boiled. Also determine the composition of both substances in the vapors formed .Solution: Being an ideal system apply Equation Raoult Ideal :

yiP = xiPvap where : yi is the mole composition of the substance i in the gas phase xi is the mole composition of the substance i in the liquid phase P is the total pressure of the system PVAP is the vapor pressure of the substance i First, the substance i refers to any component of the mixture and in this case i = 1 = ethyl alcohol; i = 2 = water. Also, in our case , Xagua = xEtílico = 0.40 = 1 - 0.60 = xEtílico and the system pressure , P = 90 kPa

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The vapor pressure is defined as the tendency of a substance in liquid phase to volatilize and is a function of temperature PVAP = f (T) . At higher temperatures , higher vapor pressure and a greater tendency of the substance to volatilize since most easily accomplished overcome opposite total system pressure. When the vapor pressure of the substance equals the total system pressure , the substance begins to boil , i.e. , the rate of volatilization is maximized .

This trend is exemplified for water, in the following table :

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With the system at a total pressure of one atmosphere ( 101.3 kPa ) , we note that for data at 20 is difficult to volatilize water and boil less . As the temperature increases in turn increases the vapor pressure , and to reach 100 equal the opposing pressure thereby establish a frank boiling . If the temperature is above that point the tendency of the system is to completely change the supersaturated vapor .

This is illustrated in the following diagram

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To calculate the vapor pressure equations are several , but one of the most used is the Antoine equation . This mathematical correlation provides very good approximations to the actual values. It consists of three constants that incorporate the characteristic properties of each substance and the temperature of the system :

wherein A, B and C constants specific Antoine for each substance T [° C ] and PVAP in [kPa ]

Continuing our case study, we have

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Antoine correlation using vapor pressures for water at various temperatures were calculated as shown in the following table . It also includes the margin of error introduced when applied . As can be seen in Table No. 2, for the most commonly used substances accuracy is guaranteed .

In calculating bubble , as the temperature is unknown , we can not assess the vapor pressure . However we can find the saturation temperature of each substance despejándola Antoine equation and using the Total System Pressure.

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Knowing the saturation temperatures can find a first value of the temperature of the system, through a weighted formula or cast :

With this initial value the saturation pressures is calculated. Then he returns to the Raoult equation applied to a selected species and compositions are evaluated in the vapor phase.

The process is repeated until the convergence temperature according to a set tolerance . Finally concentrations are calculated on the volatile phase .

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Experimentación

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RAOULT´s LAW

PROCEDURE

A. Prepare solution of methanol (1) and isopropanol ( 2) , in which the concentration of methanol (1) varies from 0.0 to 1.0 frac.mol .

B. Each solution Measure the refractive index (n) and draw a graph of n vs x1 ( calibration curve)

C.-Place the solution in the container first team on the hot plate with a slow stirring , heat to boiling , expected to be steady and record ( temperature bubble)

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D.- Extrusion equipment that has coolant foot , take a sample through a thin pipette and a knob ( deposit in a pre-labeled tube and cap ) , if the solution is pure is not necessary

E.-Repeat steps for each solution C and D

F.-Wait for samples containing condensate to reach room temperature to measure the refractive index of each

G.- Using the calibration curve to determine the mole fraction of methanol vapors at the time of vapor - liquid equilibrium

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ARTICLE

Thermodynamics of mixtures strong negative deviations from Raoult´s law. XIII. Relative permittivities for (1-alkanolt + cyclohexylamine) systems, and dielectric study of (1- alkanol + polar) compoud (amine, amide or ether) mixtures.

“the joural of chemical Thermodyamics . February 2015. Vol.,91

Juan A. González, Luis Sanz,…, José C.

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