Heat, Temperature, and Thermal Energy

• Heat and temperature are related but distinct concepts.
• The difference between heat and temperature is important to understand.

Increasing Temperature

• The temperature of water in a beaker can be increased with a heat source like a flame or a hot plate.

Thermal Energy and Mass

• More thermal energy is required to increase the temperature of a larger mass of water by the same amount.
• For example, increasing the temperature of 375,000 kg of water in a swimming pool by 10°C requires more thermal energy than increasing the temperature of 0.25 kg of water by the same amount.

Thermal Energy Defined

• Thermal energy is the energy stored in a substance due to the movement of its particles.
• It is measured in joules.

Thermal Energy Transfer

• Thermal energy can be transferred between objects through:
  • Conduction, which involves direct contact
  • Convection, which involves energy transfer through molecular motion
  • Radiation, which involves energy transfer by electromagnetic waves

Heat Defined

• Heat is a form of energy that is transferred between systems/objects with different temperatures.
• Heat measures the total energy of vibrating particles in an object.
• The volume of water being the same and one having a higher temperature than the other means the hotter one has greater thermal energy.

Temperature and Particle Motion

• When the thermal energy of an object increases, its particles vibrate faster.
• An increase in thermal energy in a substance can lead to a change in phase (e.g., liquid to gas).

Volume of water and Thermal Energy

• Even when the temperature is constant, for example two glasses of water the same temperature:
  • A larger volume of water has more particles
  • Therefore it possesses greater total thermal energy.

Temperature Defined

• Temperature isn't the same as heat, but indicates:
  • The direction of thermal energy transfer
  • The average energy of the particles in an object

Ice Cream

• Ice cream melts faster on a hot day because the air in the room is at a higher temperature. This is a temperature different of 44°C (from -20 to 24°C).
• Thermal energy transfers from the air to the ice cream due to the temperature difference.
• Thermal energy transfer is faster when there is a larger temperature difference between two objects.

Temperature and Particle Energy

• Higher temperature water contains particles moving faster.
• The soup and water are made from different materials, so they have different types of particles.
• When temperature is higher, like for soup compared to water, this means the average energy of the particles is higher even if the number of particles is the same.
• Temperature tell us the average energy of particles.

Comparing Particle Energy

• Temperature serves as a good method for comparing particle energy between objects that vary in size or are from different materials.

Defining Heat and Temperature

• Heat is defined as the transfer of thermal energy from a hotter to a cooler temperature.
• Temperature is a measure of the average kinetic energy of particles.

Sparkler Temperature

• One spark from a sparkler at 1000 °C doesn't cause burns, because the mass of the spark is very small.
• As such, the total thermal energy or heat of the sparkle is very small.
• Due to the large temperature difference between the spark and the air, thermal energy is quickly transferred from the spark to the surrounding air.
• As it travels to your skin, the spark has decreased in temperature and heat.

Temperature Reduction and Particle Movement

• A scientist called Kelvin predicted that the particles would stop if the temperature is low enough.
• As the temperature of an object decreases, the particles move more slowly.
• If particles stop moving, this is the lowest possible temperature.

Kelvin & Absolute Zero

• The lowest possible temperature in the universe is absolute zero.
• Absolute zero is -273°C, or 0 Kelvin.
• It's not actually possible to make particles completely stop moving, but scientists have come close to absolute zero in laboratories.

Important takeaway

• Heat is the total thermal energy in an object.
• Temperature is the average energy of the particles in an object.