A student heats a block of ice at 0 °C until it completely melts into water at 0 °C. Explain, using the particle model, the changes to the internal energy and the arrangement of particles during this process.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The internal energy of the ice increases.
The increase comes from an increase in the potential energy of the particles.
The supplied heat is used to overcome the attractive forces between the particles.
The particles change from a fixed, regular arrangement to a random, disordered arrangement, allowing them to slide past each other.
The increase comes from an increase in the potential energy of the particles.
The supplied heat is used to overcome the attractive forces between the particles.
The particles change from a fixed, regular arrangement to a random, disordered arrangement, allowing them to slide past each other.
Examiner tips
- Use the word "increase" for internal energy; mention "potential energy". Show the heat is used to break intermolecular forces. Describe the change from a crystal lattice to a fluid arrangement. Keep the answer concise to fit 4 marks.
Common mistakes
- Confusing kinetic energy with potential energy. Forgetting that the temperature remains 0 °C. Describing the ice as a liquid before melting is complete.
Mark scheme (4 marks)
- The internal energy of the substance increases.
- This increase in internal energy is due to an increase in the potential energy of the particles.
- The energy supplied is used to overcome the forces of attraction between the particles.
- The particles change from a fixed, regular arrangement to a random, disordered arrangement, allowing them to slide past each other.