Question

What type of forces, intramolecular or intermolecular, (a) Prevent ice cubes from adopting the shape of their container? (b) Are overcome when ice melts? (c) Are overcome when liquid water is vaporized? (d) Are overcome when gaseous water is converted to hydrogen gas and oxygen gas?

Short answer

a. Intermolecular, b. Intermolecular, c. Intermolecular, d. Intramolecular

Step-by-step solution

Define Intramolecular and Intermolecular Forces

Intramolecular forces are the forces within a molecule that keep the atoms together, such as covalent bonds. Intermolecular forces are the forces between molecules, such as hydrogen bonds, dipole-dipole interactions, and Van der Waals forces.

Analyze Part (a) - Ice cubes not adopting the shape of their container

Ice cubes retain their shape due to the strong hydrogen bonds between water molecules in the solid state. These forces are intermolecular because they occur between molecules.

Analyze Part (b) - Forces overcome when ice melts

When ice melts, the hydrogen bonds between water molecules are overcome. These are intermolecular forces.

Analyze Part (c) - Forces overcome when water vaporizes

During vaporization, the intermolecular forces (hydrogen bonds) between liquid water molecules are overcome to form gaseous water.

Analyze Part (d) - Forces overcome in converting gaseous water to hydrogen and oxygen gases

Converting gaseous water to hydrogen and oxygen involves breaking covalent bonds within the water molecules, which are intramolecular forces.

Key concepts

hydrogen bonds

Hydrogen bonds are a special type of intermolecular force. They occur when a hydrogen atom is attracted to a highly electronegative atom like oxygen, nitrogen, or fluorine in another molecule. In water, hydrogen bonds form between the hydrogen atom of one water molecule and the oxygen atom of another.
• These bonds are crucial for the unique properties of water.
• They are responsible for water's high boiling point and its solid state (ice) being less dense than its liquid form.
When ice forms, hydrogen bonds arrange water molecules into a crystalline structure. This is why ice retains its shape and does not conform to the shape of its container. When ice melts and becomes water, these hydrogen bonds are broken, but only enough to allow molecules to move more freely.

phase transitions

Phase transitions are the changes that occur when a substance changes from one state of matter to another. Common phase transitions include melting (solid to liquid), freezing (liquid to solid), vaporization (liquid to gas), and condensation (gas to liquid).
• When ice (solid water) melts into liquid, intermolecular hydrogen bonds are overcome.
• Further heating causes the liquid water to overcome more hydrogen bonds and transition to gaseous water (vaporization).
These transitions are governed by the energy required to overcome intermolecular forces. No chemical bonds within the molecules themselves are broken during these processes; only the interactions between molecules are affected.

covalent bonds

Covalent bonds are a type of intramolecular force, meaning they occur within the molecule itself. These bonds form when atoms share electrons to achieve a full outer shell of electrons, stabilizing them.
• In a water molecule, each hydrogen atom forms a single covalent bond with the oxygen atom.
Chemical reactions, like the splitting of water into hydrogen and oxygen gas, involve breaking these covalent bonds. This is a different process from phase transitions because it changes the actual chemical structure of the molecules. So, converting gaseous water to hydrogen and oxygen gases involves breaking these very strong intramolecular forces.

states of matter

States of matter refer to the distinct forms that different phases of matter take on. We commonly encounter matter in solid, liquid, and gas states.
• Solids have fixed shapes due to strong intermolecular forces holding their molecules in place.
• Liquids flow and take the shape of their container, as their molecules are less tightly packed but still interact through intermolecular forces.
• Gases have no fixed shape or volume, as their molecules are far apart and interact minimally.
In the context of water, its state depends on temperature and pressure, influencing the strength and nature of the intermolecular forces like hydrogen bonds. Understanding these states helps explain why ice cubes stick together and resist changing shape, why water flows but remains cohesive, and why steam expands to fill any available space.