Chapter 16 Thermal Energy and Heat

Chapter 16Thermal Energy and Heat 16.1 Thermal Energy and Matter

Work and Heat Heatis the transfer of thermal energy from one object to another because of a temperature difference. Heat flows spontaneously from hot objects to cold objects.

Temperature Temperature is related to the average kinetic energy of the particles in an object due to their random motions through space.

Temperature Temperatureis a measure of how hot or cold an object is compared to a reference point. • On the Celsius scale, the reference points are the freezing and boiling points of water. • On the Kelvin scale, absolute zero is defined as a temperature of 0 kelvins.

Thermal Energy Thermal energy is related to 2 variables: Thermal energy is the total potential and kinetic energy of all the particles in an object. It depends on the mass, temperature, and phase (solid, liquid, or gas) of an object.

Thermal Contraction and Expansion Thermal expansionis an increase in the volume of a material due to a temperature increase. It occurs when particles of matter move farther apart as temperature increases.

Specific Heat Specific heatis the amount of heat needed to raise the temperature of one gram of a material by one degree Celsius. The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.

Specific Heat In this formula, heat is in joules, mass is in grams, specific heat is in J/g•°C, and the temperature change is in degrees Celsius.

Specific Heat Calculating Specific Heat An iron skillet has a mass of 500.0 grams. The specific heat of iron is 0.449 J/g•°C. How much heat must be absorbed to raise the skillet’s temperature by 95.0°C?

Specific Heat Calculating Specific Heat Mass of iron m = 500g Specific heat c=20449J/g∙°C Change in temp ΔT = 95 °C Q = 500 x .449 x 95 Q = 21,375 J = 21.4 kJ

Specific Heat A calorimeteris an instrument used to measure changes in thermal energy. The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.

Specific Heat According to the law of conservation of energy, the thermal energy released by a test sample is equal to the thermal energy absorbed by its surroundings. The calorimeter is sealed to prevent thermal energy from escaping.

Specific Heat A calorimeter is used to measure specific heat. A sample is heated and placed in the calorimeter. The temperature change is observed.

Assessment Questions • What is the thermal energy of an object? • the total number of atoms or molecules • the total kinetic energy of the atoms or molecules • the average kinetic energy of the atoms or molecules • the average mechanical energy of the atoms or molecules

Assessment Questions 2. What causes a gas to expand when its temperature is increased? • The number of particles increases as temperature increases. • Each particle expands as its temperature increases, so the total volume increases. • As temperature increases, more electrons leave atoms and move separately. • As gas particles move faster, they overcome some forces of attraction.

Assessment Questions 3. The specific heat of water is 4.18 J/g•°C. How much heat is required to raise the temperature of 1,000 grams of water by 50°C? • 83.6 J • 83.6 kJ • 209 J • 209 kJ

Assessment Questions 4. What property of matter can be measured using a calorimeter? • temperature • thermal expansion • specific heat • mass

Assessment Questions 5. Temperature is the transfer of thermal energy from one object to another.TrueFalse

Chapter 16Thermal Energy and Heat 16.2 Heat and Thermodynamics

Conduction Conductionis the transfer of thermal energy with no overall transfer of matter. Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often.

Conduction Conduction occurs within a material or between materials that are touching. In conduction, collisions between particles transfer thermal energy, without any overall transfer of matter.

Conduction Thermal Conductors A thermal conductor is a material that conducts thermal energy well.

Conduction Thermal Insulators A material that conducts thermal energy poorly is called a thermal insulator.

Convection Convectionis the transfer of thermal energy when particles of a fluid move from one place to another. Convection currents are important in many natural cycles, such as ocean currents, weather systems, and movements of hot rock in Earth’s interior.

Convection A convection currentoccurs when a fluid circulates in a loop as it alternately heats up and cools down. • Air at the bottom of an oven heats up, expands, and becomes less dense. The hot air rises. • Rising hot air cools as it moves away from the heat source. • As a result, the coolest air is at the top of the oven.

Radiation Radiationis the transfer of energy by waves moving through space. All objects radiate energy. As an object’s temperature increases, the rate at which it radiates energy increases.

Heat Transfer Question • Identify the method of heat transfer in the following: an egg cooking in a frying pan; a warm air mass bringing a change in weather; the wire of an electric appliance becoming hot; heat from a fireplace warming a room

Thermodynamics The study of conversions between thermal energy and other forms of energy is called thermodynamics.

Thermodynamics First Law of Thermodynamics The first law of thermodynamics states that energy is conserved.

Thermodynamics Second Law of Thermodynamics The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects only if work is done on the system.

Thermodynamics A heat engineis any device that converts heat into work. • The efficiency of a heat engine is always less than 100 percent. • Thermal energy that is not converted into work is called waste heat. • Waste heat is lost to the surrounding environment.

Thermodynamics Spontaneous changes will always make a system less orderly, unless work is done on the system.

Thermodynamics Third Law of Thermodynamics The third law of thermodynamics states that absolute zero cannot be reached.

Assessment Questions • What form of energy transfer requires the motion of particles of a fluid? • conduction • convection • radiation • insulation

Assessment Questions • What happens in every case in which energy is added to a system? • Temperature increases. • Work is done on the system. • All of the energy can be accounted for as work or heat. • An identical amount of energy is removed from the system.

Assessment Questions • Thermal energy can move from a cooler object to a warmer object when • the warmer object is larger. • the cooler object has more thermal energy. • energy is transferred by radiation. • work is done on the system.

Assessment Questions • According to the third law of thermodynamics, it is impossible • to cool an object to absolute zero. • transfer thermal energy from a cooler object to a warmer object. • convert energy from one form to another. • account for all of the energy in a system.

Assessment Questions 5. All metals are good thermal insulators.TrueFalse

Chapter 16 Thermal Energy and Heat