Transcript Chapter 9: Heat - Mrs. Sepulveda's Classes

Chapter 9: Heat
Section 9.1: Temperature and Thermal
Equilibrium
Defining Temperature
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Temperature: a
measure of the
average kinetic
energy of the particles
in a substance
Adding or removing
energy usually
changes temperature
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Internal Energy: energies
associated with atomic
motion
Thermal Equilibrium: the
state in which two bodies
in physical contact with
each other have identical
temperatures
Increasing the temperature
of a gas at constant
pressure causes the
volume of the gas to
increase (thermal
expansion)
Measuring Temperature
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Thermometer a device that measures temperature.
Mercury
Alcohol
Metal coils
Digital
Measuring Temperature
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Calibrating thermometers requires fixed temperatures.
Measuring Temperature
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TF  Tc  32
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T  Tc  273 .15
Example Problem
Oxygen condenses into a liquid at approximately at 90.2
K. To what temperature does this correspond on both the
Celsius and Fahrenheit temperature scales?
T  Tc  273.15
Tc  T  273.15 
Tc  90.2  273.15  182.95
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TF  Tc  32
5
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TF  (182.95)  32  297.31
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Section 9.2: Defining Heat
Heat and Energy
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Heat: energy transferred
between objects because of a
difference in their
temperatures.
Energy is transferred as heat
from objects with higher
temperatures to those with
lower temperatures.
The greater the temperature
difference is between objects,
the greater the rate of
energy transfer between them
as heat.
Units of Heat
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Heat is measured in units of joules(J)
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1 calorie (cal) = 4.186 J

1 kilocalories(kcal) = 4186 J
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1 Calorie = 1kcal = 4186 J
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1 British thermal unit = 1055 J
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1 therm = 1.055 X 10⁸ J
Thermal Conduction
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Thermal conduction is the transfer of energy from
differences in temperature. Energy between
particles as they collide within a substance or
between two objects in contact.
The rate of thermal conduction depends on the
substance.
o
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Substances that rapidly transfer energy as heat are
called thermal conductors.
Substances that slowly transfer energy as heat are
called thermal insulators.
Convection and radiation also transfer
energy.
 Convection involves the
movement of cold and hot
matter.
 Electromagnetic radiation is
when objects reduce their
internal energy by giving off
electromagnetic radiation of
particular wavelengths or are
heated by electromagnetic
radiation.
Heat and Work
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The sum of the changes in potential, kinetic, and
internal energy is equal to zero.
Conservation of Energy
PE + KE + U = 0
If changes in internal energy are taken into account,
the total energy is conserved.
Sample Problem
What is the change in internal energy when the change
in potential energy is 20 J and the change in kinetic
energy is 35 J?
Given: ΔPE = 20 J
ΔKE = 35 J
Unknown: ΔU = ?
ΔPE + ΔKE + ΔU = 0
20 J + 35 J + ΔU = 0
ΔU = -55 J
Section 9.3: Changes in Temperature
and Phase
Specific Heat Capacity
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Specific Heat Capacity: the energy required to
change the temperature of 1 kg of a substance by
1°C
Q  m cT
Q = energy transferred as heat (J)
 m = mass of substance (kg)
 C = specific heat capacity
 ΔT = temperature change ( K or C)
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Calorimetry: method used to determine specific heat
capacity
The energy absorbed by one substance is equal to
the energy lost by another.
Qlost = Qgained
Example Problem
What is the final temperature when a 3.0 kg gold bar at
99°C is dropped into 0.22 kg of water at 25°C?
(Cp x m x ΔT)water = (Cp x m x ΔT) gold
(4186J/kg°C)(0.22kg)(Tf - 25°C) = (129J/Kg°C)(3.0k g)(99°C- Tf)
921Tf – 23,023 = 38,313 – 387Tf
1308 Tf = 61,336
Tf =47 ° C
Phase Change & Latent Heat
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Phase Change: physical change of a substance from
one state to another at constant temperature and
pressure
When substances melt, freeze, boil, condense, or
sublime, the energy added or removed changes the
internal energy without changing the temperature.
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Latent Heat: energy per unit mass that is transferred during
a phase change of a substance
Formula of latent heat:
Q  mL
J
Latent heat is measured in the units kg .
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Lf = Heat of fusion, the latent heat of a substance that is
melting.
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Lv = Heat of vaporization, the latent heat of a substance
that is vaporizing.