HEAT

Chapter Eleven: Heat

11.1 Heat

11.2 Heat Transfer

Chapter 11.1 Learning Goals

Describe the relationship between heat, temperature, and thermal energy.

Identify and use different units to measure heat.

Explain how the specific heat of different materials can be used to describe changes in temperature and energy.

Investigation 11A

Key Question:

How are temperature and heat related?

Temperature and Heat

11.1 What is heat?Heat is thermal energy

that is moving.Heat flows any time there

is a difference in temperature.

Because your hand has more thermal energy than chocolate, thermal energy flows from your hand to the chocolate and the chocolate begins to melt.

11.1 What is heat?

Heat and temperature are related, but are not the same thing.

The amount of thermal energy depends on the temperature but it also depends on the amount of matter you have.

11.1 Units of heat and thermal energy

The metric unit for measuring heat is the joule.

This is the same joule used to measure all forms of energy, not just heat.

11.1 Heat and thermal energyThermal energy is often measured in

calories. One calorie is the amount of energy it

takes to raise the temperature of one milliliter of water by one degree Celsius.

11.1 Specific heatThe specific heat is

a property of a substance that tells us how much heat is needed to raise the temperature of one kilogram of a material by one degree Celsius.

Knowing the specific heat of a material tells you how quickly the temperature will change as it gains or loses energy.

11.1 Why is specific heat different for different

materials?Temperature measures the average kinetic energy per particle.

Energy that is divided between fewer particles means more energy per particle, and therefore more temperature change.

In general, materials made up of heavy atoms or molecules have low specific heat compared with materials made up of lighter ones.

How much heat is needed to raise the temperature of a 250-liter hot tub from 20°C to 40°C?

Solving Problems

1. Looking for: …amount of heat in joules

2. Given: V = 250 L, 1 L of water = 1 kg Temp changes from 20°C to 40°C Table specific heat water = 4, 184 J/kg°C

3. Relationships: E = mCp(T2 – T1)

Solving Problems

4. Solution: E = (250L × 1kg/L) × 4,184 J/kg°C (40°C - 20°C)

= 20,920,000 JSig. fig./Sci. not. 20,920,000 J = 2.1 x 107 J

Chapter Eleven: Heat

11.1 Heat

11.2 Heat Transfer

Chapter 11.2 Learning Goals

Compare and contrast various methods of heat transfer.

Differentiate between thermal conductors and thermal insulators.

Explain what it means when objects are in thermal equilibrium.

Investigation 11B

Key Question:What is the identity of an unknown metal

sample?

The Specific Heat of a Metal

11.2 Heat transfer Thermal energy flows from

higher temperature to lower temperature. This process is called heat transfer.

There are three ways heat flows: heat conduction, convection, and thermal radiation.

11.2 Heat transferHeat conduction is

the transfer of heat by the direct contact of particles of matter.

Conduction occurs between two materials at different temperatures when they are touching each other.

Where is the heat energy conducted to and from in this system?

11.2 Heat transferThermal equilibrium occurs when two bodies have the same temperature.

No heat flows in thermal equilibrium because the temperature is the same in the two materials.

11.2 Thermal conductors and insulators

Materials that conduct heat easily are called thermal conductors and those that conduct heat poorly are called thermal insulators.

Is a down coat a conductor or an insulator?

11.2 ConvectionConvection is the transfer of heat through the

motion of matter such as air and water.The hot water at the bottom of the pot rises

to the top and replaces the cold water.

11.2 ConvectionConvection is mainly what distributes heat throughout a room.

11.2 Thermal radiationHeat from the Sun is

transferred to Earth by thermal radiation.

All the energy the Earth receives from the Sun comes from thermal radiation.

The higher the temperature of an object, the more thermal radiation it emits.

11.2 Thermal radiationThermal radiation is also

absorbed by objects.The amount of thermal

radiation absorbed depends on the surface of a material.

Dark surfaces absorb most of the thermal radiation they receive.

Silver or mirrored surfaces reflect thermal radiation.

11.2 Heat transfer, winds, and currentsA thermal is a

convection current in the atmosphere.

When a surface, like a road absorbs solar radiation, it emits energy as heat.

The warmed air molecules gain kinetic energy and rise.

Colder air is forced aside and sinks.

11.2 Thermal radiationThere are giant convection currents in Earth’s atmosphere.

The global wind patterns and Earth’s rotation also cause surface ocean currents to move in large circular patterns.

Investigation 11C

Key Question:Can the mass of an object

be determined without the use of a balance?

Mass Determination

Needed: Efficient Buildings“Green” building design is the term used to describe architecture that is energy-efficient and environmentally friendly.