Transcript Slide 1

Temperature
The temperature in a substance is
proportional to the average kinetic
energy of particles in the substance.
 Energy must be either added to or
removed from a substance to change its
temperature.
 The energies associated with atomic
motions are referred to as internal
energy, which is proportional to the
substances temperature.

Internal Energy
For an ideal gas, the internal energy
depends only on the temperature of the
gas
 As the gas’s temperature decreases, so
does its pressure.
 For nonideal gases, as well as for liquids
and solids, other properties contribute to
the internal energy.

Thermal Equilibrium
Thermal equilibrium is the basis for
measuring temperature with
thermometers.
 If the temperature of a substance
increases, so does its volume which is
known as thermal expansion.
 The thermal expansions characteristics
of a material are indicated by a quantity
called the coefficient of volume
expansion.

Scales
Temperature scales most widely used
today are Fahrenheit, Celsius, and
Kelvin.
 The ice point or melting point is at 0°C,
32°F, 273.15 K and the steam point or
boiling point is 100°C, 212°F, 373.15 K.

Temperature Conversions
Celsius-Fahrenheit Conversion
Tf = 9/5 Tc + 32.0
Fahrenheit temperature=(9/5xCelcius temperature)+32.0
Celsius-Kelvin Conversion
T = Tc + 273.15
Kelvin Temperature = Celsius temperature + 273.15
Example Problem

The melting point of gold is 1947°F. Express this
temperature in degrees Celsius and in Kelvin's.
Tf=1947°F
Tc=?
T=?
Tf = 9/5 Tc + 32.0
5/9 Tf – 32.0 = Tc
5/9(1947°F)-32.0 = 1049.6°C
T = Tc + 273.15
1049.6°C + 273.15 = 1322.8 K
Tc = 1049.6°C
T = 1322.8 K
Heat and Energy
Heat is sometimes used to refer to the
process by which energy is transferred
between two objects because of a
difference in their temperatures.
 Energy transferred as heat tends to
move from an object at higher
temperature or higher kinetic energy to
an object at lower temperature or lower
kinetic energy.
 Heat is indicated by the symbol Q.

Heat and Energy
When two substances become in thermal
equilibrium, the net energy transferred
between the two substances is zero. This is
the difference between temperature and
heat.
 Because temperature is a measure of
energy, all objects have some temperature.
 Heat is the energy transferred from one
object to another because of the
temperature difference. When there is no
temperature difference, no net energy is
transferred as heat.

Thermal Conduction
Thermal conduction can be understood by
the behavior by the atoms in a metal.
 The rate of thermal conduction depends on
the properties if the substance being
heated.
 Substances that rapidly transfer are called
thermal conductors and substances that
slowly transfer are called thermal
insulators.

Convection and Radiation
Convection involves the movement of cold
and hot matter.
 In electromagnetic radiation energy objects
reduce their internal en energy by giving off
electromagnetic radiation of particular
wavelengths or are heated by
electromagnetic radiation.
 The sum of the changes in potential,
kinetic, and internal energy is equal to
zero.

Conservation of energy
ΔPE + ΔKE + ΔU = 0
The change in potential energy + the change
in kinetic energy + the change in internal
energy = 0
Specific Heat
The specific heat capacity of a
substance is defined as the energy
required to change the temperature of 1
kg of that substance by 1°C.
 The same change in energy will cause
different temperature change in equal
masses of different substances due to
the differences in the motion of atoms
and molecules at the microscopic level.

Specific Heat Capacity
Cp = Q/mΔT
specific heat capacity = energy transferred as
heat / mass x change in temperature
Calorimetry
Calorimetry is used to determine specific
heat capacity. It contains both a
thermometer to measure the final
temperature of substances at thermal
equilibrium and a stirrer to ensure the
uniform mixture of energy throughout the
water.
 Energy conservation can be used to
calculate the specific heat capacity, cpx, of
the substance.

Qw = -Qx
Qw + Qx = 0
cpw · mw · ΔTw = -cpx · mx · ΔTx
energy absorbed by water = energy released by the
substance
w will always stand for water in problems involving specific heat
capacities.
Latent Heat



When substances melt, freeze, boil, condense,
or sublime, the energy added or removed
changes the internal energy of the substance
without changing the substances temperature
is known as a phase change.
Phase changes result from a change in the
potential energy between particles of a
substance.
The energy that is added or removed per unit
mass is called latent heat, abbreviated at L.
Q = mL
energy transferred as heat = mass x latent
heat