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Cox chart :

The chart, known as the Cox chart, uses a logarithmic scale for thevapor pressure and an entirely arbitrary scale for the temperature in °F.The vapor pressure curve for any particular component, as shown in Figure15-1, can be defined as the dividing line between the area wherevapor and liquid exists. If the system pressure exists at its vapor pressure,two phases can coexist in equilibrium. Systems represented by pointslocated below that vapor pressure curve are composed only of the vaporphase. Similarly, points above the curve represent systems that exist inthe liquid phase. These statements can be conveniently summarized bythe following expressions:• p < pv → system is entirely in the vapor phase• p > pv → system is entirely in the liquid phase• p = pv → vapor and liquid coexist in equilibriumwhere p is the pressure exerted on the pure component. Note that theabove expressions are valid only if the system temperature T is below thecritical temperature Tc of the substance.

The vapor pressure chart allows a quick determination of pv of apure component at a specific temperature. For computer and spreadsheetapplications, however, an equation is more convenient.

1) A straight-line graph of the logarithm of vapor pressure against a specialnonuniform temperature scale; vapor pressure-temperature lines for manysubstances intersect at a common point on the Cox chart.

2)Cox chartMolecular formula :CAS :nature : Linear said the liquid vapor pressure and temperature of a map. If

elected to vapor pressure and temperature on a straight line, said the coordinates,then it is by a minority of the data, it is easy to figure out a wide range of vaporpressure values. The plan by E. R. Cox in the 1923's, its longitudinal coordinates ofthe vapor pressure values, and the abscissa used by the water vapor pressure (on

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numerical) and the temperature linear drawing from the special temperaturecalibration. The coordinates of the other liquid vapor pressure (on numerical), therelationship between temperature and become straight. Cox called this straight line

Making a Cox chart:

1. Mark on the horizontal scale values of log p* so as to cover the desired range of p* forthecompound of interest

2. Next draw a straight line on the plot at a suitable angle, say 45⁰, that covers the rangeof Tthat is to be marked on the vertical axis

3. To calibrate the vertical axis in comm. on integers such as 25, 50, 100, 200 degrees,and soon, you use a reference substance, namely water. for the index tic mark for the firstinteger, say 100⁰F, you look up a vapor pressure of water at 100⁰ F in the steam tables,orcalculate it from the Antoine equation, to get 0.9487 psia. Locate 0.9487 psia on thehorizontal axis, and proceed vertically until you hit the 45⁰ straight line. Then proceedhorizontally left until you hit the vertical axis. Mark the scale at the intersection at100⁰F4. Pick the next temperature, say 200⁰F, for which the vapor pressure of water 11.525psia.From 11.525 psia on the horizontal axis proceed vertically to the 45⁰ straight line, andthenhorizontally to the vertical axis. Mark the scale at the intersection with the vertical axisat200⁰F5. Continue as in 3 and 4 until the vertical scale is established over the desired rangefor theTemperature

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Here are two possible forms of the Antoine's equation:

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Here are two possible forms of the Antoine's equation:

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Here are two possible forms of the Antoine's equation: