internal energy

• What is meant by internal energy?

  It is the energy stored in a system by the particles.
• What happens when a material changes state?

  The internal energy of the material changes.
• How do particles behave in a solid?

  They do not move from place to place but vibrate.
• How do particles behave in a liquid?

  They can move around each other.
• How do particles behave in a gas?

  They move extremely rapidly.
• What type of energy do all particles possess?

  They possess kinetic energy.
• What is the definition of internal energy?

  It is the total kinetic and potential energy of all the particles in a system.
• What gives particles potential energy?

  The intermolecular forces and chemical bonds between them.
• Why is internal energy important during changes of state?

  It determines the state of the material as it changes.
• What do we call the process when a solid turns into a liquid?

  Melting.
• What happens to the internal energy of a solid when it is heated?

  The internal energy increases.
• What happens to the internal energy of a liquid when it is heated?

  The internal energy continues to increase.
• What do we call the process when a liquid turns into a gas?

  Boiling.
• What happens to the internal energy of a gas when it is cooled down?

  The internal energy is reduced.
• What do we call the process when a gas turns back into a liquid?

  Condensation.
• What happens to the internal energy of a liquid when it is cooled down further?

  The internal energy is reduced even more.
• What do we call the process when a liquid turns into a solid?

  Freezing.
• What is sublimation?

  It is when a solid turns directly into a gas.
• What happens to mass during changes of state?

  Mass is always conserved.
• What type of changes are changes of state?

  They are physical changes.
• What happens when ice melts to water and then refreezes?

  The ice is exactly the same as it was at the start.
• What is evaporation?

  It is when a liquid turns to a gas only on the surface.
• What are the key points about internal energy and changes of state?

  • Internal energy is the total kinetic and potential energy of particles.
  • Changes of state involve melting, boiling, condensation, and freezing.
  • Mass is conserved during changes of state.
  • Changes of state are physical changes, not chemical changes.
  • Evaporation occurs only at the surface of a liquid.
• Which particles can turn into a gas during evaporation?

  Only the particles on the surface have enough energy.