A bowl of hot soup is left on a table in a room that is at a temperature of 18∘C18^\circ\text{C}18∘C. What has happened to the soup after fifteen minutes?
The average kinetic energy of its particles has decreased.
Its internal energy has increased.
All of its particles have the same energy.
Its particles move more quickly.
321 exam-style questions on CIE IGCSE Physics 2.1 Kinetic particle model of matter, covering 2.1.1 States of matter and changes of state, 2.1.2a Particle structure and motion in solids, liquids and gases, 2.1.2b Gas pressure and particle collisions, 2.1.2c Brownian motion, 2.1.3a The absolute scale of temperature, and 2.1.3b Pressure, volume and temperature of a gas. Each one has a worked solution and a mark scheme showing where the marks go.