Multiple choice questions in organic chemistry.

1.        1.      Which of the following statements are true about the processes of melting and freezing? (Select all that apply.)

2.        Melting requires an input of energy to convert a solid to a liquid.

3.        Melting occurs when energy is released from the substance.

4.        Freezing occurs when a liquid becomes a solid and energy is released.

5.        Freezing requires an input of energy to convert a liquid to a solid.

1.        2.      What is an elastic collision? (13.1)

2.        A collision in which all particles have no energy.

3.        A collision in which no kinetic energy is lost.    

4.        A collision in which no thermal energy is lost.

5.        A collision in which all particles keep the same amount of energy.

1.        3.      In a methane molecule (CH4), there are 4 single covalent bonds. In an octane molecule (C8H18), there are 25 single covalent bonds. How does the number of bonds affect the dispersion forces in samples of methane and octane? Which compound is a gas at room temperature? Which is a liquid? (Select which of the following statements are true.)

2.        Methane is a liquid.

3.        Octane is a gas.

4.        More bonds mean more electrons to form temporary dipoles, which means greater dispersion forces.

5.        Methane is a gas.

6.        Every bond contributes one dispersion force, therefore more bonds means more dispersion forces.

7.        Octane is a liquid.

8.        Because methane has fewer bonds, it is able to have more dispersion forces.

1.        4.      Why are most solids denser than most liquids at the same temperature?

2.        Solids are generally formed at lower temperatures.

3.        Their particles are not held as tight by covalent forces, allowing them to be held more closely together.    

4.        Their particles are held more closely together by intramolecular attractions.

5.        Their particles are held more closely together by intermolecular attractions.

1.        5.      Why are dipole-dipole forces stronger than dispersion forces for molecules of comparable mass?

2.        Dipole-dipole forces go to the gym.

3.        Dipole-dipole forces exist between permanent dipoles; dispersion forces exist between temporary dipoles.    

4.        Dipole-dipole forces exist between temporary dipoles; this allows them to be momentarily stronger.

5.        Dipole-dipole forces include dispersion forces so they are always stronger.

6.        Dispersion forces exist in non-polar molecules only; this makes them weak.

1.        6.      Which of the molecules listed below can form hydrogen bonds? (Select all that apply.)

1.        HF

2.         NH3

3.        H2

4.         HCl

           Why?

For which of the molecules would dispersion forces be the only intermolecular force?

1.        3HF

2.         H2

3.         HCl

4.        NH3

            Why?