CAS CH 101 Lecture Notes - Lecture 14: Dimethyl Ether, Intermolecular Force, Boiling Point

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8 Oct 2015

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Ch 101 - lecture 14 - intermolecular forces, dissolving ionic solids. Near boiling point, polarity is less important than dispersion. Order of dipoles when determining relative boiling points: Question: identify the compound with the smallest energy of vaporization (kj/mol). Water and ethanol both contain hydrogen bonds (in its chemical formula oxygen is attached to hydrogen). Thus, we can rule out these compounds since hydrogen bonds will increase the amount of energy of vaporization. Dimethyl ether is polar, however, remember that polarity is not a factor when it is near the boiling point. Thus, take in consideration of the size of each molecule. The greater the size, the greater the boiling point. Dimethyl ether will have the smallest energy of vaporization. Question: the correct order of boiling point of ch3oh, ch4, s=c=o, and xe is(lowest to highest) Ch3oh contains a hydrogen attached to the oxygen indicating hydrogen bonds. Thus, ch3oh should have the greatest boiling point.

Related Questions

* Circle the intermolecular force(s) that is/are present in each of the following species. [Hint: there may be more than one correct answer.]

Ar (hydrogen bonding, dipole-dipole forces, dispersion forces)

CH4 (hydrogen bonding, dipole-dipole forces, dispersion forces)

HBr (hydrogen bonding, dipole-dipole forces, dispersion forces)

HF (hydrogen bonding, dipole-dipole forces, dispersion forces)

CHCl3 (hydrogen bonding, dipole-dipole forces, dispersion forces)

* For the following pairs of atoms/molecules, circle the species that has the higher boiling point.

Ne or Xe

Cl2 or F2

HBr or HF

HCl or HI

H2O or H2S

* Phase changes always associate with change of enthalpy. For the following situations, name the phase

transition and indicate whether the process is exothermic or endothermic.

(a) Dry ice (solid carbon dioxide) turns to gaseous carbon dioxide.

Answer:

(b) Water vapor turns to liquid water.

Answer:

(d) Iodine vapor turns to solid iodine.

Answer:

(e) Liquid helium turns to helium gas.

Answer:

* True or false

1. Intermolecular forces are stronger than ionic and covalent bonds. Answer:

2. For molecules with similar size and molar mass, those with higher polarity would have higher boiling

point. Answer:

3. Ion-dipole forces exist between ionic potassium bromide and polar water.

Answer:

4. Dispersion forces exist between argon and helium. Answer:

5. Instantaneous dipoles exist in all molecules and atoms. Answer:

6. The strength of dispersion forces depends on the molar mass but the shape of the molecules have no effect on dispersion forces. Answer:

7. Ice has a higher density than water because ice has an ordered cagelike structure. Answer:

8. Liquids with weaker intermolecular interactions have lower viscosity. Answer:

9. Viscosity decreases with increasing temperature. Answer:

10. For any molecules, the heat of vaporization is always lower than the heat of fusion because it takes more energy to make molecules to move past one another in a solid lattice. Answer:

Phase changes always associate with change of enthalpy. For the following situations, name the phase transition and indicate whether the process is exothermic or endothermic.

. Dry ice (solid carbon dioxide) turns to gaseous carbon dioxide. Answer:

. Water vapor turns to liquid water. Answer:

. Solid iron turns to liquid iron. Answer:

. Iodine vapor turns to solid iodine. Answer:

. Liquid helium turns to helium gas. Answer:

True or false

. Intermolecular forces are stronger than ionic and covalent bonds. Answer:

. For molecules with similar size and molar mass, those with higher polarity would have higher boiling point. Answer:

. Ion-dipole forces exist between ionic potassium bromide and polar water. Answer:

. Dispersion forces exist between argon and helium. Answer:

. Instantaneous dipoles exist in all molecules and atoms. Answer:

. The strength of dispersion forces depends on the molar mass but the shape of the molecules have no effect on dispersion forces. Answer:

. Ice has a higher density than water because ice has an ordered cagelike structure. Answer:

. Liquids with weaker intermolecular interactions have lower viscosity. Answer:

. Viscosity decreases with increasing temperature. Answer:

. For any molecules, the heat of vaporization is always lower than the heat of fusion because it takes more energy to make molecules to move past one another in a solid lattice. Answer:

How to do these problems. Also I know the equation for molality is mol/kg so how do you do this with number 1?

CAS CH 101 Lecture Notes - Lecture 14: Dimethyl Ether, Intermolecular Force, Boiling Point

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