Download Ch 16 Thermal Energy and Heat

Physical Science. Chapter 16: Thermal Energy and Heat
16.1 Thermal energy and Matter
A. Work and Heat
 Heat is the transfer of thermal energy from on e object to another because of a temperature difference
 Heat flows spontaneously from hot objects to cold objects.
B. Temperature
 Temperature is a measures of how hot or cold an object is compared to a reference point
 In the Kelvin temperature scale the reference point is absolute zero, which is defined as a temperature of 0
K.
 Temperature is related to the average kinetic energy of the particles in an object due to their random
motions through space
 As an object heats up the particles move faster
C. Thermal Energy
 Thermal energy is the total potential and kinetic energy of all the particles in an object
 Thermal energy depends on the mass, temperature, and phase (solid, liquid, or gas) of an object.
 An object with a higher temperature has a higher average kinetic energy
D. Thermal Contraction and Expansion
 Thermal expansion is an increase in the volume of a material due to a temperature increase
 Thermal expansion occurs when particles of matter move farther apart as temperature increases
 Gasses expand more than liquids and liquids usually expand more than solids
E. Specific Heat
 Specific heat (c) is the amount of heat need 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 is measures in joules per gram per degree Celsius, or J/g∙C

The heat (Q) absorbed by a material equals the produce of the mass (m), the specific heat (c) and the
change in temperature (T).
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Heat is in joules, mass is in grams, specific heats is in J/g∙C, and temperature change is in C.
F. Measuring Heat Changes
 A calorimeter is an instruments used to measure changed in thermal energy.
 A calorimeter used the principle that heats flows from a hotter object to a colder object until both reach the
same temperature.
 According to the law of conservations of energy, the thermal energy released by the sample is equal to the
thermal energy absorbed by its surrounds.
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16.2 Heat and Thermodynamics
A. Conduction
 Conduction is the transfer of thermal energy with no overall transfer of matter
 Conduction occurs within a material or between materials that are touching
 Conduction is gases is slower than in liquids and solids because the particles in a gas collide less often.
 In most solids, conduction occurs as particles vibrate in place and push on each other.
1. Thermal Conductors
o Thermal conductor is a material that conducts thermal energy well
o Metals conducts thermal energy very quickly
o Tile is a better conductor than wood and transfers thermal energy
2. Thermal Insulators
o Thermal insulator is a material that conducts thermal energy poorly
o Air is a very good insulator
o Wool garments and plastic foam cups are two more examples of insulators
B. Convection
 Convection is the transfer of thermal energy when particle of a fluid move from one place to another
 Air circulating in an oven is an example of a convection current
 Convection current occurs when a fluid circulates in a loop as it alternately heats up and cools down.
 Convection currents are important in many natural cycles (ocean currents, weather systems, and moved of
hot rocks in earth’s interior
C. Radiation
 Radiation is the transfer of energy by waves moving through space
 Heat lamps and the sun are examples of radiations
 All objects radiate energy. As an object’s temperature increase, the rate at which it radiates energy
increases.
D. Thermodynamics
 Thermodynamics is the study of conversions between thermal energy and other forms of energy
1. First law of Thermodynamics
o Energy cannot be created or destroyed but id can be converted into different forms.
o The first law of thermodynamics stats that energy is conserved
o If energy is added to the systems it increases the thermal energy of the system or does work on the
system.
2. Second Law of Thermodynamics
o Thermal energy flows spontaneously only from otter t colder objects
o The second law of thermodynamics stats that thermal energy can flow form colder objects to hotter
objects only if works is done on the system.
o Heat engine is any device that converts heat into work.
o The efficiency of a heat engine is always less than 100 %
o Waste heat is thermal energy that is not converted into work
o Waste heat is lost to the surrounding environment
3. Third Law of Thermodynamics
o The efficiency of a heat engine increases with a greater difference between the high temperature
inside and the cold temperature outside the engine
o The thirds law of thermodynamics stats that absolute zero cannot be reached
o Scientists have been able to cool mater almost all of the way to absolute zero
o