When a substance is heated, two primary things happen to its particles:

1. Increased Kinetic Energy: The particles gain more kinetic energy, meaning they move faster and vibrate more vigorously. This increased movement is what makes the substance feel hotter.

2. Increased Distance Between Particles: The increased kinetic energy also causes the particles to move further apart. This leads to expansion of the substance, whether it be a solid, liquid, or gas.