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Why does CCl4 have a higher boiling point than CHCl3 even though CCl4 is non-polar and CHCl3 is polar?
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Posted by
Nathaniel Rob
Why does CCl4 have a higher boiling point than CHCl3 even though CCl4 is non-polar and CHCl3 is polar?
The molecular mass of CCl4 is 153.82 amu. Its boiling point is 76.72 degrees C.
The molecular mass of CHCl3 is 119.38 amu. Its boiling point is 61.2 degrees C.
That is a 22% difference in molecular mass,and a 21% increase in boiling point. Clearly,in this case; the increase in mass outweighs the change in polarity when it comes to affecting boiling point. In fact,since the increases in mass and boiling point are so similar; That leads me to ask..what actually is the dipole moment of CHCl3?
dipole moment of CHCl3 = 1.01 debye. This is really not very high (less than CH2Cl2 at 1.6 D) and is easily canceled out by the large change in mass.
The molecular mass of CCl4 is 153.82 amu. Its boiling point is 76.72 degrees C.
The molecular mass of CHCl3 is 119.38 amu. Its boiling point is 61.2 degrees C.
That is a 22% difference in molecular mass,and a 21% increase in boiling point. Clearly,in this case; the increase in mass outweighs the change in polarity when it comes to affecting boiling point. In fact,since the increases in mass and boiling point are so similar; That leads me to ask..what actually is the dipole moment of CHCl3?
dipole moment of CHCl3 = 1.01 debye. This is really not very high (less than CH2Cl2 at 1.6 D) and is easily canceled out by the large change in mass.
Tetrachloromethane (CCl4) consists of non-polar molecules interacting via dispersion forces, whereas trichloromethane (CHCl3) consists of polar molecules interacting via permanent dipole-permanent dipole (pd-pd) interactions.
To answer this question simply, CCl4 has a higher boiling point than CHCl3 because dispersion forces in CCl4 is extensive enough to be stronger than pd-pd interactions in CHCl3.
Now, I know textbooks always say that the general rule of thumb is that pd-pd interactions are stronger than dispersion forces. There are, however, many exceptions to this rule of thumb, and this is due to the various other factors that affect the overall strength of inter-molecular forces.
Some of the factors that affect overall strength of intermolecular forces are listed below:
Strength of each intermolecular interaction (I.e. what textbooks say about one hydrogen bond > one pd-pd interaction > one dispersion force)
Extensiveness of intermolecular interactions (Imagine intermolecular interactions as “bonds” between molecules, how many of such “bonds” can be formed between two molecules. I’ll elaborate on this below)
Thermodynamic changes such as entropy (Explained in detail in some of the other responses)
Etc
Comparing CCl4 and CHCl3, CCl4 has a nicer / more symmetrical shape. Therefore, we can expect its packing to be more compact. This would mean that in a sample of CCl4, there would arguably be a greater surface area of contact between two molecules of CCl4. A greater surface area of contact would then allow for the formation of more extensive intermolecular interactions.
So in CCl4, even though the strength of each intermolecular interaction is weaker compared to CHCl3, the extensiveness of intermolecular interaction in CCl4 far exceeds that in CHCl3 such that the overall strength of intermolecular interactions in CCl4 is stronger than that in CHCl3.
To put this explanation into perspective, a calculation using arbitrary values is shown below:
Strength of one dispersion force = 4 Strength of one pd-pd interaction = 7 [Because pd-pd interaction is stronger than dispersion force]
Max. no. of intermolecular “bonds” between two molecules of CCl4 = 50 Max. no. of intermolecular “bonds” between two molecules of CHCl3 = 25 [Because CCl4 can be packed more compactly]
Overall strength of intermolecular “bonds” between two molecules of CCl4 = 50x4 = 200 Overall strength of intermolecular “bonds” between two molecules of CHCl3 = 25x7 = 175
Tetrachloromethane (CCl4) consists of non-polar molecules interacting via dispersion forces, whereas trichloromethane (CHCl3) consists of polar molecules interacting via permanent dipole-permanent dipole (pd-pd) interactions.
To answer this question simply, CCl4 has a higher boiling point than CHCl3 because dispersion forces in CCl4 is extensive enough to be stronger than pd-pd interactions in CHCl3.
Now, I know textbooks always say that the general rule of thumb is that pd-pd interactions are stronger than dispersion forces. There are, however, many exceptions to this rule of thumb, and this is due to the various other factors that affect the overall strength of inter-molecular forces.
Some of the factors that affect overall strength of intermolecular forces are listed below:
Strength of each intermolecular interaction (I.e. what textbooks say about one hydrogen bond > one pd-pd interaction > one dispersion force)
Extensiveness of intermolecular interactions (Imagine intermolecular interactions as “bonds” between molecules, how many of such “bonds” can be formed between two molecules. I’ll elaborate on this below)
Thermodynamic changes such as entropy (Explained in detail in some of the other responses)
Etc
Comparing CCl4 and CHCl3, CCl4 has a nicer / more symmetrical shape. Therefore, we can expect its packing to be more compact. This would mean that in a sample of CCl4, there would arguably be a greater surface area of contact between two molecules of CCl4. A greater surface area of contact would then allow for the formation of more extensive intermolecular interactions.
So in CCl4, even though the strength of each intermolecular interaction is weaker compared to CHCl3, the extensiveness of intermolecular interaction in CCl4 far exceeds that in CHCl3 such that the overall strength of intermolecular interactions in CCl4 is stronger than that in CHCl3.
To put this explanation into perspective, a calculation using arbitrary values is shown below:
Strength of one dispersion force = 4 Strength of one pd-pd interaction = 7 [Because pd-pd interaction is stronger than dispersion force]
Max. no. of intermolecular “bonds” between two molecules of CCl4 = 50 Max. no. of intermolecular “bonds” between two molecules of CHCl3 = 25 [Because CCl4 can be packed more compactly]
Overall strength of intermolecular “bonds” between two molecules of CCl4 = 50x4 = 200 Overall strength of intermolecular “bonds” between two molecules of CHCl3 = 25x7 = 175
The molecular mass of CCl4 is 153.82 amu. Its boiling point is 76.72 degrees C.
The molecular mass of CHCl3 is 119.38 amu. Its boiling point is 61.2 degrees C.
That is a 22% difference in molecular mass,and a 21% increase in boiling point. Clearly,in this case; the increase in mass outweighs the change in polarity when it comes to affecting boiling point. In fact,since the increases in mass and boiling point are so similar; That leads me to ask..what actually is the dipole moment of CHCl3?
dipole moment of CHCl3 = 1.01 debye. This is really not very high (less than CH2Cl2 at 1.6 D) and is easily canceled out by the large change in mass.
The molecular mass of CCl4 is 153.82 amu. Its boiling point is 76.72 degrees C.
The molecular mass of CHCl3 is 119.38 amu. Its boiling point is 61.2 degrees C.
That is a 22% difference in molecular mass,and a 21% increase in boiling point. Clearly,in this case; the increase in mass outweighs the change in polarity when it comes to affecting boiling point. In fact,since the increases in mass and boiling point are so similar; That leads me to ask..what actually is the dipole moment of CHCl3?
dipole moment of CHCl3 = 1.01 debye. This is really not very high (less than CH2Cl2 at 1.6 D) and is easily canceled out by the large change in mass.
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Tetrachloromethane (CCl4) consists of non-polar molecules interacting via dispersion forces, whereas trichloromethane (CHCl3) consists of polar molecules interacting via permanent dipole-permanent dipole (pd-pd) interactions.
To answer this question simply, CCl4 has a higher boiling point than CHCl3 because dispersion forces in CCl4 is extensive enough to be stronger than pd-pd interactions in CHCl3.
Now, I know textbooks always say that the general rule of thumb is that pd-pd interactions are stronger than dispersion forces. There are, however, many exceptions to this rule of thumb, and this is due to the various other factors that affect the overall strength of inter-molecular forces.
Some of the factors that affect overall strength of intermolecular forces are listed below:
Comparing CCl4 and CHCl3, CCl4 has a nicer / more symmetrical shape. Therefore, we can expect its packing to be more compact. This would mean that in a sample of CCl4, there would arguably be a greater surface area of contact between two molecules of CCl4. A greater surface area of contact would then allow for the formation of more extensive intermolecular interactions.
So in CCl4, even though the strength of each intermolecular interaction is weaker compared to CHCl3, the extensiveness of intermolecular interaction in CCl4 far exceeds that in CHCl3 such that the overall strength of intermolecular interactions in CCl4 is stronger than that in CHCl3.
To put this explanation into perspective, a calculation using arbitrary values is shown below:
Strength of one dispersion force = 4
Strength of one pd-pd interaction = 7
[Because pd-pd interaction is stronger than dispersion force]
Max. no. of intermolecular “bonds” between two molecules of CCl4 = 50
Max. no. of intermolecular “bonds” between two molecules of CHCl3 = 25
[Because CCl4 can be packed more compactly]
Overall strength of intermolecular “bonds” between two molecules of CCl4 = 50x4 = 200
Overall strength of intermolecular “bonds” between two molecules of CHCl3 = 25x7 = 175
Hope this explains things clearly.
Tetrachloromethane (CCl4) consists of non-polar molecules interacting via dispersion forces, whereas trichloromethane (CHCl3) consists of polar molecules interacting via permanent dipole-permanent dipole (pd-pd) interactions.
To answer this question simply, CCl4 has a higher boiling point than CHCl3 because dispersion forces in CCl4 is extensive enough to be stronger than pd-pd interactions in CHCl3.
Now, I know textbooks always say that the general rule of thumb is that pd-pd interactions are stronger than dispersion forces. There are, however, many exceptions to this rule of thumb, and this is due to the various other factors that affect the overall strength of inter-molecular forces.
Some of the factors that affect overall strength of intermolecular forces are listed below:
Comparing CCl4 and CHCl3, CCl4 has a nicer / more symmetrical shape. Therefore, we can expect its packing to be more compact. This would mean that in a sample of CCl4, there would arguably be a greater surface area of contact between two molecules of CCl4. A greater surface area of contact would then allow for the formation of more extensive intermolecular interactions.
So in CCl4, even though the strength of each intermolecular interaction is weaker compared to CHCl3, the extensiveness of intermolecular interaction in CCl4 far exceeds that in CHCl3 such that the overall strength of intermolecular interactions in CCl4 is stronger than that in CHCl3.
To put this explanation into perspective, a calculation using arbitrary values is shown below:
Strength of one dispersion force = 4
Strength of one pd-pd interaction = 7
[Because pd-pd interaction is stronger than dispersion force]
Max. no. of intermolecular “bonds” between two molecules of CCl4 = 50
Max. no. of intermolecular “bonds” between two molecules of CHCl3 = 25
[Because CCl4 can be packed more compactly]
Overall strength of intermolecular “bonds” between two molecules of CCl4 = 50x4 = 200
Overall strength of intermolecular “bonds” between two molecules of CHCl3 = 25x7 = 175
Hope this explains things clearly.
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