Question

question 23 of 30
which statement best describes the intermolecular forces between h₂ molecules and nh₃ molecules in the liquid phase?

a. dipole-dipole forces are the strongest force between h₂ molecules, and van der waals forces are the strongest force between nh₃ molecules.

b. van der waals forces are the strongest force between h₂ molecules, and hydrogen bonding is the strongest force between the nh₃ molecules.

c. hydrogen bonding is the strongest force between h₂ molecules and between nh₃ molecules.

d. van der waals forces are the strongest force between h₂ molecules and between nh₃ molecules.

Explanation:

1. Analyze \( \ce{H_2} \) molecules: \( \ce{H_2} \) is a non - polar molecule. The intermolecular forces between non - polar molecules are Van der Waals forces (also known as London dispersion forces). There is no dipole - dipole interaction (since it is non - polar) and no hydrogen bonding (hydrogen bonding requires a hydrogen atom bonded to a highly electronegative atom like N, O, or F, and in \( \ce{H_2} \), H is bonded to H).
2. Analyze \( \ce{NH_3} \) molecules: \( \ce{NH_3} \) is a polar molecule with a lone pair of electrons on the N atom. The N - H bonds are polar, and since N is a highly electronegative atom, \( \ce{NH_3} \) molecules can form hydrogen bonds with each other. Hydrogen bonding is a stronger intermolecular force than Van der Waals forces and dipole - dipole forces (in the case of \( \ce{NH_3} \), hydrogen bonding is the dominant strong intermolecular force).
3. Evaluate the options:

• Option A: \( \ce{H_2} \) is non - polar, so dipole - dipole forces are not present between \( \ce{H_2} \) molecules. And \( \ce{NH_3} \) has hydrogen bonding, not just Van der Waals forces as the strongest force. So A is incorrect.
• Option B: For \( \ce{H_2} \) (non - polar), Van der Waals forces are the strongest intermolecular force. For \( \ce{NH_3} \), hydrogen bonding is the strongest intermolecular force. This option is correct.
• Option C: \( \ce{H_2} \) molecules do not have hydrogen bonding (no H bonded to N, O, or F in \( \ce{H_2} \)). So C is incorrect.
• Option D: \( \ce{NH_3} \) has hydrogen bonding as the strongest intermolecular force, not just Van der Waals forces. So D is incorrect.

Answer:

B. Van der Waals forces are the strongest force between \( \ce{H_2} \) molecules, and hydrogen bonding is the strongest force between the \( \ce{NH_3} \) molecules.