# Chapter 21 Temperature_ Heat_ and Expansion by dfhdhdhdhjr

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```									Temperature, Heat, and
Expansion
Chapter 21
Temperature
 Temperature – the quantity that tells how hot
or cold something is compared with a standard
 A common thermometer measures temperature
by showing the expansion and contraction of a
liquid in a glass tube using a scale
 Celsius Scale – most widely used temperature
scale, 0ºC is the point at which water freezes
and 100ºC the point at which water boils, the
gap between is divided into 100 equal parts
Temperature
 Fahrenheit Scale – commonly used in
the U.S., has 180ºF between freezing and
boiling (32ºF and 212º)
 Kelvin Scale – used in scientific
research, degrees are the same size as
Celsius + 273º, denoted K
 Absolute Zero – the lowest possible
temperature on the Kelvin scale,
substance has no kinetic energy
Thermometers
Scale Comparison
Temperature and Kinetic Energy
 In an ideal gas, temperature is
proportional to the average kinetic energy
 The heat that you feel when you touch a
hot surface is the kinetic energy
transferred by molecules in the surface to
 Temperature is not a measure of the total
kinetic energy
Heat
   Heat – the energy that transfers from one
object to another because of a temperature
difference between them
   Matter does not contain heat, but contains
energy in several forms
   Heat is energy in transit
   Internal Energy – the energy resulting from heat
flow
   When heat flows from one object or substance
to another it is in contact with, the objects are
said to be in thermal contact
   Heat flows from the higher-temperature
substance into the lower-temperature substance
Heat Flow Between Two Gases
Thermal Equilibrium
 Thermal Equilibrium – objects in
thermal contact with each other reach the
same temperature, no heat flows between
them
 When reading a thermometer, we wait
until the thermometer has reached
thermal equilibrium with the object we
want the temperature of
Thermal Equilibrium
Internal Energy
 Internal Energy – the total of all
energies inside a substance
 A substance does not contain heat – it
contains internal energy
 When a substance takes in or gives off
heat, any of these energies can change
Internal Energy
Measurement of Heat
   To quantify heat, we have to specify the mass and
kind of substance affected
   Calorie – the most commonly used unit for heat;
the amount of heat required to raise the
temperature of 1 gram of water by 1ºC
   Kilocalorie – the heat required to raise 1 kilogram
of water by 1ºC (1000 calories)
   The heat unit for rating foods is actually the
kilocalorie (to distinguish from calorie, it is often
written as Calorie)
   Remember that a calorie is a measure of ENERGY!
   The relationship between calories and joules is:
1 calorie = 4.184 Joules
Calories
Specific Heat Capacity
 Different substances have different capacities for
storing internal energy
 We find that specific materials require specific
quantities of heat to raise the temperature of a
given mass of the material by a specified number of
degrees
 Specific Heat Capacity – the quantity of heat
required to raise the temperature of a unit mass of a
substance by 1ºC
Q = mcΔT
Q = quantity of heat; m = mass of substance;
c = specific heat capacity of substance;
ΔT = change in temperature
 We can think of specific heat capacity as thermal
inertia (an object’s resistance to change)
Specific Heat Capacities
Thermal Expansion
 When the temperature of a substance increases,
the molecules “jiggle” faster and move further
apart, causing an expansion of the substance
 Gases generally expand and contract more than
liquids, which expand and contract more than
solids
 In concrete sidewalks and highways this
expansion and contraction is taken into account
when it is being built. The surface is laid down
in small sections with a gap in between, that is
usually filled with a substance such as tar.
Thermal Expansion

Expansion Joint
Expansion of Water
 Almost all liquids will expand when they
contracts to go from ice to a liquid
 When the water reaches a temperature of
4ºC, it will stop contracting and begin
expanding
 This has to do with the crystal structure of
water, its solid state has an open structure
that takes up more volume and is
therefore less dense
Expansion of Water
Assignment – Due Tuesday 1/22
 Read Chapter 21 (pg. 307-321)
 Do Chapter 21 #19-39 (pg. 323-324)

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