Question

Overall which forces are responsible for Enplaination of Ice(s)

• A. Dipole - Dipole
• B. Dipole -$\frac{ID}{\text{Induced Dipole}}$
• C. LDF
• D. All of these

Answer 1

Answer: (A)

A

Answer 2

The question asks which forces are responsible for the "Enplaination" of Ice(s). Assuming "Enplaination" is a typo for "Expansion" or "Explanation" of the unique properties of ice, particularly its lower density compared to liquid water.

1. Understanding Water and Ice:

   • Water (H₂O) is a highly polar molecule due to the bent shape and the electronegativity difference between oxygen and hydrogen.
   • Because of its polarity, water molecules exhibit dipole-dipole interactions.
   • Crucially, water molecules can form hydrogen bonds. Hydrogen bonding is a special, strong type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom (like O, N, or F) and is attracted to a lone pair on another electronegative atom in an adjacent molecule.
   • All molecules, including water, also experience London Dispersion Forces (LDFs), which are weak, temporary attractive forces arising from instantaneous dipoles.

2. Structure and Density of Ice:

   • In liquid water, hydrogen bonds are constantly forming and breaking, allowing molecules to pack relatively closely.
   • When water freezes to form ice, the molecules arrange themselves into a highly ordered, open, cage-like hexagonal lattice structure. Each water molecule forms four hydrogen bonds with neighboring molecules, creating a tetrahedral arrangement around each oxygen atom.
   • This open structure means that the water molecules in ice are further apart on average than in liquid water. This increased volume for a given mass results in ice having a lower density than liquid water, causing it to float and to expand upon freezing.

3. Identifying the Responsible Forces:

   • The unique expansion of ice and its lower density are directly attributable to the formation of this specific, open, hydrogen-bonded network.
   • Therefore, hydrogen bonding is the primary force responsible for this phenomenon.
   • Hydrogen bonding is a specific and strong type of dipole-dipole interaction.

4. Evaluating the Options:

   • Ⓐ Dipole-Dipole: This category includes hydrogen bonding, which is the direct cause of ice expansion. So, this is a correct and comprehensive answer.
   • Ⓑ Dipole-Induced Dipole: These interactions occur between a polar molecule and a non-polar molecule, or when a polar molecule induces a temporary dipole in another. While they might be present to a very minor extent, they are not the primary forces responsible for the unique structure and expansion of ice.
   • Ⓒ LDF (London Dispersion Forces): LDFs are present in all molecules, including water. However, they are relatively weak compared to hydrogen bonds and do not explain the unique expansion property of ice. The expansion is due to the specific geometrical arrangement dictated by the hydrogen bonds, not LDFs.
   • Ⓓ All of these: While LDFs and dipole-dipole interactions (including hydrogen bonding) are present in ice, LDFs and dipole-induced dipole interactions are not the cause of the expansion. The question asks for the forces responsible for the expansion. Therefore, "All of these" is incorrect because it implies all listed forces are equally responsible, which is not true for the expansion phenomenon.

Conclusion: The expansion of ice is a direct consequence of the specific, open structure formed and stabilized by hydrogen bonds. Hydrogen bonding is a type of dipole-dipole interaction. Therefore, dipole-dipole interactions are the overall forces responsible.