10.1 - Internal Energy & Changes of State

Heating or cooling changes temperature or state

• Heating transfers energy to the particles in a substance; cooling transfers energy away.
• Heating or cooling leads to a temperature change or a change of state.

Heating and cooling

• Temperature change - Heating makes particles move or vibrate faster, raising the temperature. Cooling slows particles down, lowering the temperature.
• Change of state - If heated enough, the energy breaks the bonds between particles rather than raising their temperature. When cooled enough, bonds form between particles.

Temperature stays constant during a change of state

• While a substance is changing state, its temperature does not change.
• During melting or boiling, energy is absorbed to break bonds rather than raise the temperature.
• During condensing or freezing, bonds form and release energy, so the temperature does not fall until the change of state is complete.
• Melting point is the temperature at which a substance melts; boiling point is the temperature at which it boils.
• For pure water at normal atmospheric pressure: melting point 0 °C, boiling point 100 °C.

Internal energy

• The particles that make up a substance are constantly moving or vibrating, so they have energy in their kinetic energy stores.
• The total energy of all the particles in a substance is the energy in its internal energy store.

Temperature and internal energy

1. Heating a substance transfers energy to its particles, making them move faster.
2. This increases the average energy in their kinetic stores, which raises the temperature and increases the substance's internal energy.