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 energy  Thermal 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 heat  The 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 = mC p (T 2 – T 1 ) Solving Problems 4.Solution:  E = (250L × 1kg/L) × 4,184 J/kg°C (40°C - 20°C) = 20,920,000 J Sig. fig./Sci. not. 20,920,000 J = 2.1 x 10 7 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 transfer  Heat 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 transfer  Thermal 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 Convection  Convection 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 Convection  Convection is mainly what distributes heat throughout a room.

11.2 Thermal radiation  Heat 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 radiation  Thermal 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 currents  A 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 radiation  There 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.