International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What happens to the arrangement of particles when a liquid cools to become a solid?

1. The arrangement becomes more random

2. The arrangement becomes more regular

3. The arrangement remains unchanged

4. The arrangement becomes less ordered

The correct answer is: The arrangement becomes more regular

When a liquid cools to become a solid, the arrangement of its particles becomes more regular. This occurs due to the decrease in thermal energy as the temperature drops. In a liquid, particles have enough energy to move around freely, resulting in a random arrangement. However, as the liquid cools, the particles lose this kinetic energy and begin to slow down. This allows intermolecular forces to take hold, reorganizing the particles into a fixed, structured arrangement characteristic of solids. In solids, particles are usually packed closely together in a fixed position, creating a regular and often orderly arrangement, which is responsible for the solid’s definite shape and volume. This transition from the disordered state of a liquid to the orderly state of a solid is why the accurate description is that the arrangement becomes more regular.