Thermal Energy

Particle Theory of Matter

• All matter is made of particles.

• Particles are always moving.

• Temperature affects the speed at which the particles are moving.

Temperature

(T) Average Kinetic Energy of the particles in a substance. Temperature is measured, use a thermometer and has the units of °C or K.

Thermal Energy #1

Total Kinetic Energy of all the particles. This can't be measured; but is calculated (J).

So 5 L of water at 80 degrees has more thermal energy than 500 mL of water at 80 degrees, but they have the same temperature.

Heat

(Q or ΔH) This is the energy transfer from hot object to a cold object (energy transit).

• Conduction. - Convection. - Radiation.

Can't be measured but is calculated (J).

What is the difference between Thermal and Heat energy?

Thermal is a property of the system (thermal is the total energy of the system), whereas heat is the energy that flows between systems because of a temperature difference (from HOT --> COLD)

Thermal Energy #2

Thermal energy is a property of the system, whereas heat is the energy that flows between systems because of a temperature difference.

What does thermal energy depend on?

Both the speed and heat of the particles.

What is the difference between 'thermal energy' and 'temperature'?

Thermal is the total kinetic energy that the particles in the substance has. Whereas the temperature is the average kinetic energy of all the particles.

Summaries

• Temperature: Average Kinetic Energy of the particles. (symbol: T) (measured in °C of K)

• Thermal Energy: Total Kinetic Energy of all the particles. (measured in J)

• Heat: Energy transfer. (symbol: Q) Calculated in Joules (J).

Convection

The transfer of heat energy by the movement of hotter less dense fluids and cooler more dense fluids. Occurs in liquids and gases.

Conduction

The transfer of heat energy by vibration of neighboring particles from a hot object to a cool one.

Radiation

The transfer of heat energy by electromagnetic waves (infra-red waves) from a hot object to a cool one.

Radiation Summary

Absorption: Black = Good, White = Poor

Release: Black = Good, White = Poor

Reflection: Black = Poor, White = Good

Thermal Conductor

An object whose structure means that energy can easily be transferred within the object e.g. metals. Their free moving electrons facilitate the transfer of Kinetic Energy.

Thermal Insulator

Objects that have a molecular structure that restricts the flow of Kinetic Energy preventing heat from being transmitted.

SOLID ------> LIQUID -------> GAS

SOLID <------- LIQUID <------- GAS

Absorbs energy to break intermolecular forces of attraction (or metallic bonds) (or ionic bonds).

melting (fusion)

boiling (evaporation/vaporisation)