WJEC GCSE Chemistry Practice Exam

At GCSE, the particle model of matter is built on three ideas: all substances are made of tiny particles; there are spaces between those particles; and the particles are in constant motion with energy that changes with temperature. The statement that lists these three ideas is the best because it directly reflects this model: every substance is composed of small particles, there are gaps between them that explain why things compress or expand, and the particles are always moving with energy that increases when you heat them and decreases when you cool them. This helps explain why different states behave differently and how heating changes things. For example, heating adds energy to the particles, making them move faster and spread out more, which can cause a solid to melt or a liquid to vaporize. On the other hand, if a statement claims particles are fixed in place at all temperatures, or that matter is continuous without particles, or that only liquids have particles, it conflicts with the observable facts that solids and gases also consist of particles and that particles are always moving to some degree.