On an atomic level, what is occurring that causes a substance to change its state (e.g., from solid to liquid or liquid to gas)?

• A. The kinetic energy of the particles increases, allowing them to overcome intermolecular forces.
• B. Electrons are transferred between atoms, causing a change in state.
• C. The number of protons in each atom changes, resulting in a new state.
• D. Atoms combine to form new elements, which leads to a change of state.

Answer: (A)

Verified step by step guidance

1. Understand that a change in state (phase change) involves a physical transformation where the substance moves between solid, liquid, and gas phases without changing its chemical identity.
2. Recognize that particles (atoms or molecules) in a substance are constantly moving and possess kinetic energy, which depends on temperature.
3. Know that intermolecular forces are the attractions between particles that hold them together in a particular state; these forces are stronger in solids and weaker in gases.
4. When heat is added, the kinetic energy of the particles increases, allowing them to overcome the intermolecular forces holding them in a fixed position or close proximity.
5. Therefore, the change of state occurs because increased kinetic energy enables particles to move more freely, transitioning from solid to liquid or liquid to gas.