Thermal Energy and Heat Chapter 14

Section 1: Temperature, Thermal Energy, and Heat

Temperature A measure of the average kinetic energy of the individual particles in matter. The faster the particles move, the more kinetic energy. We use a thermometer to measure temperature. 3 Scales: Celsius, Fahrenheit, Kelvin

Celsius scale Boiling point of water = 100˚C Freezing point of water = 0˚C Fahrenheit scale Boiling point of water = 212˚F Freezing point of water = 32˚F Kelvin scale Boiling point of water = 373K Freezing point of water = 273K

˚C = K - 273 K = C + 273 formulas Convert 303K to ˚C 303K – 273 = 30˚C Convert 70˚C to K 70˚C + 273 = 343K absolute zero = 0K or -273 ˚ C At absolute zero, there is no kinetic energy in the particles / no thermal energy can be removed

Thermal Energy and Heat Thermal Energy depends upon: 1. the number of particles in the object 2. the temperature of the object 3. the arrangement of the particles Heat is: thermal energy which moves from a warmer object to a less warm object. Example-ice cube melting in your hand

Examine the beakers below. Which beaker holds more water molecules? Which beaker has a higher temperature? Which beaker has more kinetic energy? Which beaker has more thermal energy? Which beaker has the greatest mass?

Specific Heat The amount of energy required to raise the temperature of one kilogram of a material by one Kelvin. Unit for specific heat: J/(kg*K) Formula: change in energy = mass x specific heat x change in temperature Material with a high specific heat can absorb a lot of thermal energy without a great change in temperature.

Materials with a low specific heat will absorb heat quickly and easily. Ex: Sand on the beach Ex: gold (bracelet) Ex: concrete/pavement/tar Ex: iron Ex: copper Ex: silver

Sample Problem How much heat energy is required to raise the temperature of 5kg of water by 10 Kelvins? Given information: mass = 5kg change in temp (∆T) = 10K specific heat of water = 4180J/(kg*K) Unknown: change in energy

3 Steps to Solve This Problem Formula: change in energy = mass x specific heat x ∆T Substitution: energy = 5kg x 4180J/(kg*K) x 10K Answer: 20,900 J

Section 2: The Transfer of Heat

How is Heat Transferred? 3 ways that heat can move: 1. Conduction 2. Convection 3. Radiation

Conduction Heat is transferred by the direct contact of particles Example: the heat energy from the hot soup is transferred by conduction to the spoon—the spoon then becomes warm.

Convection Heat is transferred by the movement of currents within a fluid (liquid or a gas) Example: boiling water—water is moved by the currents in the fluid When fluids are heated, the particles move faster and further apart. Pizza oven Opening an oven and feeling a blast of hot air

When fluids are heated, they rise upward because they become less dense Example: hot water/air rises and cool water/air sinks The rise and fall of these fluids create convection currents (circular motion)

Radiation The transfer of heat energy by electromagnetic waves Example: fire, sun’s energy Does not require matter to transfer thermal energy

Heat Moves One Way Heat will always flow from a warmer object to a cooler object. As thermal energy increases, the temperature of matter absorbing the heat increases. The temperature of the matter losing the thermal energy is dropping. Note: there is no such thing as “coldness”

Conductors and Insulators Conductor: material that transfers thermal energy well metal spoon most metals Insulator: material that does not transfer thermal energy well wood wool straw goose feathers/down comforter insulation

Section 3: Thermal Energy and States of Matter

States of Matter Solid Particles are packed tightly together Particles only vibrate Retain their shape and volume

Liquid particles are close together particles are free to move around does not have a definite shape has a definite volume

Gas particles are moving very fast! particles are spread very far apart gases expand to fill available space lack a fixed shape and volume

Changes of State Change of State: physical change of matter from one state of matter to another (occurs when heat energy is absorbed or released) Solid-Liquid Changes: 1. melting: solid changes to a liquid 2. freezing: liquid changes to a solid

Liquid-Gas Changes: Vaporization: change from a liquid to a gas (absorbs heat energy) 1. evaporation: vaporization that takes place at the surface of a liquid 2. boiling: vaporization that takes place below the surface of a liquid 3. condensation: a change from a gas to a liquid (cold drink in the summer-loses heat energy)

Thermal Expansion As the thermal energy of matter increases, its particles spread out and the substance expands. The expansion of matter when it is heated is thermal expansion. Example: metal grooves on a bridge