Abstract :

In this experiment we will be determine the vapour pressure of different liquid Solids as well as liquids evaporate at all temperatures. The rate of evaporation of a solid is negligible at temperatures well below its melting-point, as we may see from the fact that bars of metal do not gradually disappear. The rate of evaporation of liquids is much higher than those of solids. Thus, liquids may disappear if evaporation continues at any level of temperature.

At certain temperature, the generated saturated vapor (in contact with its own liquid) exerts a pressure on its surface. This pressure is called the vapor pressure. The pressure of the saturated vapor rises with increase of temperature. If the liquid is confined in a closed container at continuous heating the container may explode.

Results and Discussion :

T ( C ) T ( K ) P ( bar ) P ( mmhg ) lnP 1/(T+C)Intercept =

A 57.98991644

28 301 0.01 7.6 2.0281482470.00396479

3 Slope = -B-

14058.19023

30 303 0.02 15.2 2.7212954280.00393360

1

33 306 0.05 38 3.637586160.00388772

3

36 309 0.08 60.8 4.1075897890.00384290

2

39 312 0.1 76 4.330733340.00379910

3C = -48.78

0.00378 0.0038 0.00382 0.00384 0.00386 0.00388 0.0039 0.00392 0.00394 0.00396 0.003980

0.51

1.52

2.53

3.54

4.55

f(x) = − 14058.19022549 x + 57.9899164364899R² = 0.940082046256935

Ln(p) V.S. 1/(T+C)

1/(T+C)

Ln(P

)

From the above results we can notice that as temperature increase the vapor pressure will increase, because when temperature increase more molecules will gain sufficient kinetic energy to over one the attractive force between molecules of the liquid phase so the liquid molecules will leave the surface of the liquid and become vapor which caused vapor pressure is equal to the external pressure at a certain temp.

This temp is called the boiling point.

Ln Pv = A – B/ (T+C)

There are other methods to determine the vapor pressure by using Cox chart this chart gives P Vs T.

Antoine equation gives value of vapor pressure which increase with temperature, but in this experimental there are some errors came from source of error like personal errors and instrumented errors.

When you compare between tabulated data and experiment data we note different in constant value , refers to the room temperature or become from error in measured temperature .

Conclusions:

1. Vapor pressure is the pressure exerted by the vapor on the surface when it is in equilibrium with liquid.

2. Increasing the temperature will increase the exporting of the liquid so that will increase the pressure exerted by the vapor on the surface of liquid and after a certain time the pressure of the vapor will attain a constant value which called the vapor pressure of the liquid .

3. Vapor pressure of chemical liquids can be measured by different method eg.hagnant method ASTM method.

4. The normal boiling point is the point at which the vapor pressure at the liquid is equal to external pressure so that increasing the vapor pressure will case the evaporating and boiling more quickly than decreasing the vapor pressure

5. The relationship between the vapor pressure and temperature is directly proportional that give an exponential carve.

6. Volatile liquid is the liquid that evaporate immediately at a certain temperature.

7. There are some experimental error by using mechanical device so that experimental value from empirical equation.

References:

Appendices (Raw Data, Sample Calculations):

From Table (where P in mmHg ,T in K)Compound A B C T range (K)n-Hexane 15.8366 2697.55 -48.78 245-370

From experiment :Where constant A will be the intercept and constant B the slop

In the figure above the intercept is A = 59.98992

The slope will be equal −lnP1

T (K )+c

Slope = 14058.19