heat

1. Particle Theory of Matter

The Particle Theory of Matter explains the behavior and properties of all substances:

  1. All matter is made of tiny particles.

  2. Particles have empty spaces between them.

  3. Particles are moving randomly all the time.

  4. Particles move faster and spread farther apart when they are heated.

  5. Particles attract each other.

2. Energy: Types and Forms

Energy is defined as the capacity to do work or cause change.

2.1 Two Main Types of Energy

  • Kinetic Energy (K.E.=12mv2K.E.=21​mv2): The energy of an object is in motion.

  • Potential Energy (P.E.=mghP.E.=mgh): Stored energy based on an object's position or chemical state.

2.2 Forms of Energy

  • Thermal Energy: The total kinetic energy of all the particles in a substance.

  • Chemical Energy: Stored in the bonds of atoms and molecules (e.g., food, batteries).

  • Radiant Energy: Energy that travels in electromagnetic waves (e.g., light, radio waves).

  • Electrical Energy: Energy from the movement of electrons.

  • Nuclear Energy: Energy stored in the nucleus of an atom.

3. Heat vs. Temperature

While related, these two concepts measure different things:

  • Temperature (TT): A measurement of the average kinetic energy of the particles in a substance. It does not depend on the amount of matter present.

  • Heat (QQ): The transfer of energy from a substance at a higher temperature to a substance at a lower temperature. It represents the total energy moved and is measured in Joules (JJ).

4. Methods of Heat Transfer

Heat energy moves from warmer areas to cooler areas via three methods:

  1. Conduction

    • The transfer of thermal energy through direct contact between particles.

    • Occurs most efficiently in solids, such as a metal spoon heating up in a hot drink.

  2. Convection

    • The transfer of thermal energy through the movement of fluids (liquids and gases).

    • Warm, less dense fluids rise, while cooler, denser fluids sink, creating a circulation called a convection current.

  3. Radiation

    • The transfer of energy through electromagnetic waves.

    • It is the only method that can travel through a vacuum (empty space), such as heat from the Sun reaching Earth.

5. Phase Changes

Phase changes occur when heat is added or removed, causing particles to reorganize without changing the chemical identity of the substance:

  • Melting: Solid to Liquid (heat absorbed).

  • Freezing: Liquid to Solid (heat released).

  • Vaporization: Liquid to Gas (heat absorbed); includes evaporation and boiling.

  • Condensation: Gas to Liquid (heat released).

  • Sublimation: Solid directly to Gas (e.g., dry ice).

  • Deposition: Gas directly to Solid (e.g., frost forming on a window).

Note: During a phase change, the temperature of a substance remains constant because the energy is used to break or reform attractive forces between particles rather than increasing their speed.