Mastery Chapter 16
Chapter 16: What should know when we finish
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Explain how heat and work transfer energy.
Relate thermal energy to the motion of particles that make up a material.
Relate temperature to thermal energy and to thermal expansion.
Calculate thermal energy, temperature change, or mass using the specific heat equation.
Describe how a calorimeter operates and calculate thermal energy changes or specific heat using
calorimetry measurements.
Describe conduction, convection, and radiation and identify which of these is occurring in a given
situation.
Classify materials as thermal conductors or thermal insulators.
Apply the law of conservation of energy to conversions between thermal energy and other forms
of energy.
Apply the second law of thermodynamics in situations where thermal energy moves from cooler
to warmer objects.
State the third law of thermodynamics.
Chapter 16: Thermal Energy and Heat
Heat – is the transfer of thermal energy from object to another because of a temperature difference
 Heat flows spontaneously from hot objects to cold objects
Temperature – is a measure of how hot or cold an object is compared to a reference point
 Recall that on the Celsius scale, the reference points are the freezing (0°) and boiling points
(100°) of water
 On the Kelvin scale, another reference point is absolute zero, which is 0°K.
 Related to the average kinetic energy of the particles in an object due to their random motions
through space
 Remember, when an object heats up, its particles move faster on average.
How does heat flow from a high to a low temperature? It does this through collisions. On average, highenergy particles lose energy and low energy particles gain energy in collisions. So overall, collisions
transfer thermal energy from hot to cold objects.
Thermal Energy
Thermal energy - is the total potential and kinetic energy of all the particles in an object
 Recall that potential energy is the energy stored in objects
 Recall that kinetic energy is the energy of motion
 Depends on the mass, temperature, and phase of an object
Mass: A cup full of tea and a pitcher full of tea have the temperature. However, because the pitcher holds
more quantity of tea, it also has more particles than the cup. Because it contains more particles it can be
said that it has more thermal energy.
Temperature: If you take a cup of hot tea and a cup of cold tea, they both contain the same number of
particles and have the same mass. Because the particles in warmer objects move faster than the particles
in colder objects, there are more collisions taking place in the warm cup of tea. Because the particles are
moving faster, the average kinetic energy is greater and thus it contains more thermal energy.
Thermal Contraction
Have you ever taken a balloon from a warmer area to a cooler area? What happened? Thermal contraction
is what happened. As the particles in the balloon started to cool down, they started to move slower and the
pressure inside the balloon decreased causing the balloon to contract. The pressure decreased because
Mastery Chapter 16
slower particles collide less often and exert less force and it is the collisions of the particles that cause the
pressure.
Thermal Expansion: is an increase in the volume of a material due to a temperature increase
 Occurs when particles of matter move farther apart as temperature increases.
 Gases expand more than liquids and liquids expand more than solids
If you bring the balloon back into a warmer environment, the particles begin to warm up and move faster.
As the particles move faster, the number of collisions begins to increase and so does the pressure.
Specific Heat: is the amount of heat needed to raise the temperature of one gram of a material by one
degree Celsius
 Measured in J/g . °C
 The lower a materials specific heat, the more its temperature rises when a given amount energy is
absorbed by a given mass
 Q = mc∆T
Measuring Heat Changes
Calorimeter – is an instrument used to measure changes in thermal energy
 Uses the principle that heat flows from hotter to colder object until they both reach the same
temperature
 The thermal energy released by one object is equal to thermal energy absorbed by another object.
Heat and Thermal Dynamics
Conduction – is the transfer of thermal energy with no overall transfer of matter.
 It occurs within a material or between materials that are touching
 In conduction, collisions between particles transfer thermal energy, without any overall transfer
of energy
 Slower in gases than in liquids and solids because the particles in a gas collide less often.
Thermal conductor – is a material that conducts thermal energy well (metals, water)
Thermal insulator – is a material that does not conduct thermal energy well (air, plastic, rubber, wood)
Convection – is the transfer of thermal energy when particles of a fluid move from place to another.
 Convection current occurs when a fluid circulates in a loop as it alternately heats up and cools
down
Radiation – is the transfer of energy by waves moving through a space
 Heat lamps in a restaurant is a good example
Thermodynamics – the study of conversions between thermal energy and other forms of energy
 First law of thermodynamics – energy is conserved (bicycle pump)
 Second law of thermodynamics – thermal energy can flow from colder objects to hotter objects
only if work is done on the system (refrigerator)
 Third law of thermodynamics – states that absolute zero cannot be reached