This set of Physical Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Intermolecular Forces”.
1. Which of the following has the strongest intermolecular forces of attraction?
a) Water
b) Hydrogen
c) Ethane
d) Iron ball
View Answer
Explanation: The boiling points of water, hydrogen, ethane and iron ball are 100°C, -89°C, -1°C and 2750°C respectively. Higher the intermolecular forces between the molecules of the substance, higher will be its boiling point. Thus, iron ball has the strongest intermolecular forces of attraction.
2. Which of the following intermolecular forces are the strongest?
a) Dipole-Dipole Interaction
b) Intermolecular H-bonding
c) Dispersion Forces
d) Ionic bonds
View Answer
Explanation: The increasing order of the strength of intermolecular forces is dispersion forces < dipole-dipole interaction < intermolecular H-bonding < ionic bonds. Therefore, ionic bonds have the strongest intermolecular forces of attraction.
3. Boiling points are a measure of intermolecular forces.
a) True
b) False
View Answer
Explanation: Weak intermolecular forces require less energy to move the molecules apart. But if the intermolecular forces are strong, then large amount of energy will be required to oppose the force of attraction between the molecules. This energy is supplied in the form of heat when boiling. Substances with stronger bonds have high boiling points.
4. What is the effect of polarization of bonds on intermolecular forces?
a) Intermolecular forces decrease with increasing polarization of bonds
b) Intermolecular forces increase with increasing polarization of bonds
c) There is no effect of on intermolecular forces
d) Intermolecular forces increase with decreasing polarization of bonds
View Answer
Explanation: The intermolecular forces increase with increasing polarization of bonds. As bonds become more polarized, the charges on the atoms increase which results in increasing intermolecular forces between the molecules.
5. Which intermolecular forces are called as long range forces?
a) Covalent bonds
b) H-bonding
c) Van der Waals forces
d) Ionic bonds
View Answer
Explanation: Long range forces are the forces that do not need contact between the objects to exist. Van der Waal forces are called long range forces, because they act outside the 3 angstroms and are attractive in nature. They are responsible for surface tension, viscosity, friction and differences between the actions of gases.
6. Which of the following is categorized as the weakest intermolecular forces?
a) H-bonding
b) Dispersion forces
c) Dipole-dipole interaction
d) Ionic bonds
View Answer
Explanation: Dispersion forces are the weakest intermolecular forces, because these are temporarily attractive in nature. These are formed when the electrons in two adjacent atoms occupy position due to which the atoms form temporarily dipoles.
7. Which of the following hydrocarbons has the highest boiling point?
a) C3H8
b) C4H10
c) C5H12
d) C6H14
View Answer
Explanation: C6H14 is the hydrocarbon that has the highest boiling point. Non polar compounds have dispersion forces. Larger the molecule, larger will be the dispersion forces. Therefore, higher amount of energy is required to overcome the larger dispersion forces, thus C6H14 requires more energy.
8. What is the effect of atomic radius of halogens on intermolecular forces?
a) Lower atomic radius, higher intermolecular forces
b) Higher atomic radius, lower intermolecular forces
c) No effect of atomic radius on their boiling point
d) Higher atomic radius, higher intermolecular forces
View Answer
Explanation: The following table shows the increasing order of atomic radius of halogens with their respective boiling points:
| HALOGENS | ATOMIC RADIUS | BOILING POINT |
|---|---|---|
| Fluorine | 72 pm | 85K |
| Chlorine | 99 pm | 238K |
| Bromine | 133pm | 332K |
| Iodine | 133 pm | 457K |
Thus, increase in atomic radius of halogens results in increasing their boiling point, hence the intermolecular forces increase with the increase in atomic radius of the halogens.
9. Which of the following is more likely to dissolve molecular iodine into it?
a) CCl4
b) H2O
c) HCl
d) H2SO4
View Answer
Explanation: H2O, HCl and H2SO4 are polar but iodine(I2) is non-polar while carbon tetrachloride (CCl4) is also non-polar, and the principle says ‘like dissolves in like’, therefore the non-polar compound I2 is more likely to dissolve in carbon tetrachloride rather than dissolving in polar compounds.
10. Which term is used for the interaction between highly electron-deficient hydrogen and highly electronegative atom?
a) Ionic bond
b) Covalent bond
c) H-bonding
d) Dispersion forces
View Answer
Explanation: H-bonding is used for the interaction between highly electron-deficient hydrogen and highly electronegative atom. Atoms such as nitrogen, oxygen or fluorine experience attraction to some other nearby highly electronegative atom.
11. Which of the following intermolecular forces holds liquid N2 together?
a) Ionic bonding
b) London forces
c) Dipole-dipole interaction
d) Covalent bonding
View Answer
Explanation: London dispersion intermolecular forces hold liquid N2 together. Without London dispersion forces, diatomic nitrogen would not remain liquid. London forces are also called temporary or weakest intermolecular forces.
12. Which of the following phase changes are endothermic?
b) Melting and condensation
b) Sublimation and condensation
c) Vaporization and condensation
d) Melting, sublimation and vaporization
View Answer
Explanation: Melting, sublimation and vaporization, all require the input of heat to change phases, this is why these processes are endothermic in nature. Examples of endothermic are ice melting, boiling water and dry ice.
13. In any cubic lattice, an atom lying at the corner of a unit cell is shared equally by how many unit cells?
a) Eight
b) Four
c) Two
d) One
View Answer
Explanation: An atom at the corner of the cube is shared by eight adjacent cubes, and thus makes 1/8 contribution to any one cell. Similarly, the center of an edge is common to four other cells, and an atom centered in a face is shared with two cells.
14. Which of the following compounds would be expected to have the highest melting point?
a) BaI2
b) BaF2
c) BaCl2
d) BaBr2
View Answer
Explanation: Higher ionic character of bonds corresponds to the ionic potential of the cations. Higher the charge by size (smaller the size) ratio of cation, more strongly ionic compound it is and, so higher is the melting point. Thus, BaF2 has the highest melting point.
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