The Effects of Intermolecular Attractions on Evaporation and Change of Temperature








Kim Lu

SCH4U

Mr. Linzel




Introduction

Evaporation is the process in which a solution in liquid state becomes gaseous. Evaporation generally occurs on a daily basis with numerous solutions, evaporation occurs at all temperatures rather than at one specific set temperature like boiling points. Solutions can evaporate at any given temperature and evaporation occurs at the surface of the solution instead of through the solution like boiling. Evaporation deals with kinetic energy, since the average velocity of the particles in a solution are raised due to temperature increase then the particles individual velocity will rise and in turn more collisions will occur. As more collisions occur it will reach a point in which the particles of the solution’s surface will begin to be collided and hit with more force and the particles will be removed from the liquid and the surface which causes those particles to become gaseous.

Intermolecular forces are forces that hold molecules together at different strengths depending on the force itself. Hydrogen bonds are the strongest bond between molecules out of the possible three. When a hydrogen bond is present it becomes me difficult to break that bond between the molecules since the strength of the bond between the molecules is strong it then becomes more difficult for a solution in a liquid state to become gaseous which would entail bonds to be broken in turn would result in a slower evaporation rate. The weakest intermolecular force would be the London dispersion bond since the bond is the weakest it is less difficult to break apart the bonds in substances that have dispersion bonds present. Since the bonds are easier to break apart, solutions that consist of dispersion forces have a faster evaporation rate, the easier it is to break the bonds the less energy is required to do so therefore the rate of evaporation is quickened. Dipole-dipole forces are stronger then dispersion but weaker the hydrogen bonding which would directly mean its rate of evaporation is between hydrogen bonding and dispersion.

The stronger the intermolecular force is, the slower the rate of evaporation will be. The intermolecular force is directly related to the bonds between molecules and the molar mass. The hydrogen bond is the strongest bond that molecules can obtain and if the bonds between molecules are strong then the attraction allows the solution to be held in its liquid state longer. Since the bond is strong it brings difficultly to break those bonds and when a liquid evaporates or becomes gaseous bonds need to be broken to transition to a gaseous state, it requires more energy to break those strong bonds which causes the rate of evaporation to be slower. The strength of intermolecular forces is directly related to the rate of evaporation, if the evaporation rate is higher, intermolecular forces are weaker. If the rate of evaporation is slower, the intermolecular forces are stronger.


Hypothesis

With this investigation the solutions that have the stronger intermolecular forces as well as a more massive molar mass will have the evaporation that is slower and the change of temperature would be greater as well as the rate of the temperature decreasing would be less. The strength between the molecules is the key factor with regards to evaporation rate. The type of bonding and the strength of the bond is however more substantial compared to molar mass, molar mass is just a contributing factor. The solutions with hydrogen bonds have a stronger intermolecular force of attraction which allows the molecules to have a tighter hold on to each other which would cause the rate of evaporation to be slower in turn resulting in a change in temperature that is small. The more massive the molar mass result in molecules in the solution to have a greater mass and size therefore their hold is also tighter. With this investigation the solutions that have hydrogen bonds with or without a great molar mass will have slower rates of evaporation, solutions with dipole-dipole forces will follow in rate than those with dispersion forces. When a solution that has similar intermolecular forces but one has a more massive molar mass, the solution with the greater molar mass will have the slower rate of evaporation.

Method

  1. The data collection apparatuses were set up, the temperature probe was attached to the computer Labpro interface and that was connected to the laptop. The Labpro program was started and the machine and program synced.

  2. A short piece of filter paper was wrapped around the temperature probe approximately twice and then tied to the probe using a rubber band.

  3. 15 ml of ethanol was obtained, put in a test tube and a stopper was placed.

  4. The temperature probe was placed in the test tube of ethanol and the temperature was collected for 30 seconds.

  5. After 30 seconds the temperature probe was removed was placed at the edge of the table and taped down as the temperature continued to be collected until 180 seconds.

  6. The initial and final temperature was calculated using the software by determining the maximum and minimum y values between 30 seconds and 180 seconds.

  7. Steps 2-6 was continued for 1-propanol

  8. A prediction for 1-butanol and methanol was made.

  9. The prediction was tested by repeating steps 2-6 for 1-butonal and methanol.

  10. A prediction for n-hexane and n-pentane was made

  11. The prediction was tested by repeating steps 2-6 for n-hexane and n-pentane.

Safety

Table 1: Safety, Storage and Disposal Table

MSDS Categories

Methanol

Ethanol

1-propanol

1-butanol

(n) pentane

(n) hexane

Toxic

Yes if inhaled/ingested

Can Be toxic, in massive concentrations

Yes if inhaled, ingested

Yes, if inhaled can be if ingested

Yes if inhaled and ingested

Yes, if inhaled/ingested

Irritant

Yes, can be to skin and eyes

Can be irritant, in massive concentrations

Can be irritant with prolonged exposure to eyes and skin

Can be irritant to eyes and skin

Causes Dry Skin

Yes, to eyes, skin and mucous membranes

Corrosive

N/A

N/A

N/A

N/A

N/A

N/A

Flammable

Yes

Yes

Yes

Yes

Yes

Yes

Storage

Store away from heat, sparks keep in container suitable for flammable liquids

In containers suited for flammable liquids only

Ventilate well store away from heat, sparks and flames

Keep tightly contained in appropriate container away from heat sparks and flames

Keep away from open flames/sparks/

Heat, keep cooled, well ventilated, away from strong oxidants

Keep Separate from strong oxidants, keep away from flames/sparks/

heat, keep well ventilated, cool

Disposal

Dispose according to federal regulations

Dispose according to federal regulations

Dispose according to federal regulations

Dispose according to federal regulations

Dispose according to federal regulations

Dispose according to federal regulations

Precautions

Keep away from heat/sparks/open flames

Keep away from heat/sparks/open flames

Keep away from heat/sparks/open flames

Keep away from heat/sparks/

open flames

Keep away from heat/sparks/

open flames

Keep away from heat/sparks/open flames






Data Tables

Table 2: Initial, Final and Change in Temperature of Initial Substances

Solution

Initial Temp(°C)

Final Temp(°C)

Change In Temp(°C)

Ethanol

23.96

14.12

9.84

1-Propanol

23.34

17.71

 5.63


Table 3: Prediction of Changes in Temperature of Remaining Substances

Solution

Change in Temp Prediction (°C)

1-Butanol

 1-Butanol compared to 1-propanol has a higher molar mass. Since they both already have hydrogen bonds. 1-butanol will have a change in temperature that is less then 1-propanol’s change in temperature.

Methanol

 Since it does have hydrogen bonding but a fairly low molar mass. It would most likely have a fairly fast change in temperature. Compared to ethanol whose molar mass is greater then methanol, and they both do have hydrogen bonding methanol's change in temperature would be higher and its evaporation rate would be faster.

n-Pentane

Since n-pentane has no hydrogen bonding present, it is presumed that its rate of evaporation will be significantly higher then the previous substances tested due to the fact that they all had hydrogen bonds present.

n-Hexane

 Since n-hexane has no hydrogen bonding it is automatically assumed that its rate of evaporation will be fast or its change in temperature will be high. However it does have a massive molar mass which would result in a moderately slower rate of evaporation. The only other solution that does not contain hydrogen bonding is n-pentane and compared to n-pentane, n-hexane has a higher molar mass which means that n-hexane's rate of evaporation would be slower then n-pentane.


Table 4: Initial, Final and Change in Temperatures of Remaining Substances

Solution

Initial Temp(°C)

Final Temp(°C)

Change in Temp(°C)

1-Butanol

23.41

18.62

4.79

Methanol

22.78

6.037

16.743

n-Hexane

22.80

12.09

10.71

n-pentane

21.63

1.897

19.643


Data Analysis

With the substances that were tested to determine the evaporation rate it was determined that those with hydrogen bonding had a slower evaporation rate then those without hydrogen bonding present. However other factors also contributed to the results that were obtained. Molar mass as well as other types of bonding also affected the results. With regards to the results that were collected the predictions conducted previously were correct. The two substances that did not contain hydrogen bonding in this lab were the ones with the highest change in temperature which results in the highest rate of evaporation. The one out of the two that contained the higher molar mass, n-Hexane had the slower rate of reaction. With the substances with hydrogen bonding compared to the non hydrogen bonding their rate of reaction was much slower and their change in temperature was also lower. Out of the substances with hydrogen bonding the substance with the highest molar mass was 1-butonal(74.12 g/mol), and its rate of evaporation was the slowest out of all of the substances followed by 1-propanol(60.09 g/mol), ethanol(46.051 g/mol), and methanol (32.04 g/mol). Though molar mass did make an impact on the rate of evaporation, it was the type of bonding present that made the main impact on the rates of evaporation then the molar masses were the second factor that separated the solutions.

Evaluation

Since the data showed that substances with hydrogen bonding compared to the substances without hydrogen bonding had the slowest evaporation rate, this showed that those with hydrogen bonding had a stronger hold on their molecules due to the stronger intermolecular forces. It was also apparent that substances with high molar masses also had a slower evaporation rate since its molecules have a stronger mass which would result that that substance has stronger dispersion forces compared to smaller molar masses. Both the type of bonding and the molar mass are important with regards to the intermolecular forces strength therefore is important in the rate of evaporation. Molar mass was a major factor due to the fact that F=ma, or force is equal to mass times acceleration. If the mass of an object or in this case the molecules, if the mass increases then the force required to break the bonds between the molecules also increases. If the mass decreases the force decreases therefore it is easier to break those bonds between the molecules which would results in a faster rate of evaporation. Which is the reasoning behind why substances with the same type of bonding have different rates of evaporation and why the two substances in this lab that did not have any hydrogen bonding had fairly significantly different rates of evaporation. However the type of bonding is predominate compared to the molar mass. With n-pentane and 1-butanol their molar masses are fairly close however their rate of evaporation are completely different. This is due to the fact that 1-butanol has hydrogen bonding present and that molar mass is not a main factor unless it is to analyze substances that are under the same bonding categories. Since the attraction between the bonds of the 1-butanol are so much stronger then the attractions in n-pentane due to the present of hydrogen bonding it then becomes more difficult to break those bonds and more energy is required to break those bonds held by hydrogen bonding and more energy results in a slower rate of evaporation because to build up enough energy to break those bonds will take time and then it is still not a significant change in temperature because of the strength of the bonds. The substance that had the strongest bonds present was 1-butanol mainly because of the fact that its change in temperature was the lowest and its rate of reaction then was the slowest out of all of the substances. This was due to the fact of the hydrogen bonds present as well as the highest molar mass out of the hydrogen bond substances. Both factors contributed to the strength of the intermolecular bonds and resulted in the strongest intermolecular bonds. The substance that had the weakest intermolecular bonds were n-pentane of the substances without hydrogen bonds and methanol of the hydrogen bonding substances. Compared to n-hexane, n-pentane's molar mass was less massive which results in a faster rate of evaporation. Methanol had the lowest molar mass out of all of the hydrogen bonding substances which displayed the fact that its intermolecular attractions were not that strong even though it did have hydrogen bonds present its low molar mass contributed to its high change in temperature and fast rate of evaporation.