How is energy involved in the change of state, such as melting or boiling, as represented by a molecular model?

• A. Energy is only involved in chemical changes, not physical changes like changes of state.
• B. Energy remains constant and does not affect the change of state.
• C. Energy is absorbed to overcome intermolecular forces during a change of state.
• D. Energy is released to strengthen intermolecular forces during a change of state.

Answer: (C)

Verified step by step guidance

1. Understand that a change of state (such as melting or boiling) is a physical change where the substance changes from one phase to another without altering its chemical identity.
2. Recognize that during a change of state, energy is involved in overcoming or forming intermolecular forces between molecules, rather than breaking or forming chemical bonds within molecules.
3. In the case of melting or boiling, energy must be absorbed by the substance to overcome the attractive forces holding the molecules together in a solid or liquid phase, allowing them to move more freely in the next phase.
4. This absorbed energy is called the latent heat (latent heat of fusion for melting, latent heat of vaporization for boiling) and does not increase the temperature but changes the state.
5. Therefore, the molecular model shows that energy input is required to overcome intermolecular forces during a change of state, which explains why energy is absorbed during melting or boiling.