Heat and Heat Technology

Holt: Chapter 10

Fusion: Unit 4, Lessons 2-3

Temperature

• It is not simply “how hot or cold something is”

• Hot and cold are relative

• Temperature is, specifically, a measure of the average kinetic energy of the particles in an object

• All matter is made of particles that are constantly moving! (Remember the movements of solids, liquids and gasses)

• The more the particles are moving, the more kinetic energy, therefore, higher temperature

How do we measure temperature?

• Thermometers

• Thermometers can measure temperature due to thermal expansion.

• Thermal expansion is an increase in the size of a substance in response to an increase in the temperature of the substance.

• As a substance’s temperature increases, its particles move faster and spread out. There is more space between them = expansion.

The temperature scales

• You will have to know this

for your SOL test!

• 0K = absolute zero

• Absolute zero is the

temperature at which all

molecular motion stops.

Heat

• Heat is the energy transferred between objects that are different temperatures.

• When two things at different temperatures come into contact, energy is transferred from the object with the higher temperature to the object that has the lower temperature.

• The form of energy being transferred is thermal energy. Thermal energy is the total kinetic energy of the particles that make up a substance.

• More thermal energy = higher temperature

Quick check!

• Why do we use temperature instead of “hot” and “cold”?

• What are the three temperature scales?

• What is absolute zero?

3 ways to transfer thermal energy

• Conduction

•Convection

•Radiation

Conduction

• Thermal conduction is the transfer of thermal energy from one substance to another through direct contact.

• Substances that conduct thermal energy well are called thermal conductors.

• Substances that do not conduct thermal energy well are called thermal insulators.

Convection

• Convection is the transfer of thermal energy by the circulation or movement of a liquid or gas.

Radiation

• Radiation is the transfer of energy as electromagnetic waves.

Quick check!

• What are the three types of thermal energy transfer?

• What are some key words that can let you know that the type of transfer is conduction?

• Convection?

• Radiation?

Heat and Temperature Change

• Remember the concepts of insulators and conductors

• Different substances have different thermal conductivity

• Thermal conductivity is the rate at which a substance conducts thermal energy.

Specific Heat

• How easily does a material change temperature?

• Specific heat is the amount of energy needed to change the temperature of 1 kg of a substance 1 degree C. (p 285 Holt)

• The energy is measured in joules.

States of Matter

• Remember: states of matter are the physical forms of matter, which include solid, liquid and gas.

• A change of state is a change of a substance from one physical state to another.

• Is change of state a physical or chemical change?

Changes

• Heat can be involved in both physical changes (change of state) and chemical changes

• How do new bonds form in chemical reactions?

Food and Chemical Energy

• Where do we get energy?

• Energy that your body can use is released when chemical compounds such as carbohydrates are broken down. Energy is released in chemical reactions.

• You can find out how much chemical energy is in food by looking at the CALORIES on the nutrition label

• The calorie is the unit of energy in food = a measure of heat

• 1 calorie = 4184 J

Calorimeter

• A calorimeter is a device that measures heat.