mechanical equivalent of heat
.a gas usually consists of a very large number of particles, so it's convenient to express
- Answer-the amount of gas in a given volume in terms of the number of moles, n
.a gas with a larger molar specific heat requires - Answer-more energy to realize a given
temperature change
the size of the molar specific heat depends on the structure of the gas molecule and
how many different ways it can store energy
.a low-density approximates what is called an - Answer-ideal gas
most gases at room temperature and atmospheric pressure behave approximately as
ideal gases
.a mole is a number - Answer-the same number of particles is found in a mole of helium
as in a mole of iron or aluminium
this number is known as Avogardo's number
.a procedure based on two new points was adopted in 1954 by the International
Committee on Weights and Measures - Answer-the first point is absolute zero
the second point is the triple point of water, which is the single temperature and
pressure at which water, water vapor, and ice can coexist in equilibrium
this point is a convenient and reproducible reference temperature for the Kelvin scale; it
occurs at a temperature of 0.01°C and a pressure of 4.58 mm of mercury
.absolute zero is used as the basis for the - Answer-Kelvin temperature scale, which
sets -273.15°C as its zero point (0 K)
aka absolute temperature
.adiabatic processes - Answer-no energy enters or leaves the system by heat
insulated, thermally isolated from its environment
in general, however, the system isn't mechanically isolated, so it can still do work
a sufficiently rapid process may be considered approximately adiabatic because there
isn't time for any significant transfer of energy by heat
Q=0
U=W
the work done during an adiabatic process can be calculated by finding the change in
the internal energy
alternately, the work can be computed from the PC diagram
for an ideal gas undergoing an adiabatic process
PV^γ = constant
where
,γ = Cp/Cv
is called the adiabatic index of the gas
.all real engines operate - Answer-irreversibly, due to friction and brevity of their cycles,
and are therefore less efficient than the Carnot engine
.all thermometers use of some physical property that changes with temperature and can
be calibrated to make the temperature measurable - Answer-some of the physical
properties used are (1) the volume of a liquid, (2) the length of a solid, (3) the pressure
of a gas held at constant volume, (4) the volume of gas held at constant pressure, (5)
the electric resistance of a conductor, and (6) the color of a very hot object
.although we often picture an ideal gas as consisting of single atoms, molecular gases -
Answer-exhibit ideal behavior at low pressures
on average, effects associated with molecular structure have no effect on the motions
considered, so we can apply the results of the following development to molecular
gases as well as to monatomic gases
.an ideal absorber - Answer-an object that absorbs all the light radiation incident on it,
including invisible infrared and ultraviolet light
aka black body because a room-temperature black body would look black
because a black body doesn't reflect radiation at any wavelength, any light coming from
it is due to atomic and molecular vibrations alone
a perfect black body has emissivity e = 1
an ideal absorber is also an ideal radiator of energy
the Sun, for example, is nearly a perfect black body
this statement may seem contradictory because the Sun is bright, not dark; the light that
comes from the Sun, however, is emitted, not reflected
black bodies are perfect absorbers that look black at room temperature because they
don't reflect any light
all black bodies, except those at absolute zero, emit light that has a characteristic
spectrum
.an ideal gas - Answer-is a collection of atoms or molecules that move randomly and
exert no long-range forces on each other
each particle of the ideal gas is individually pointlike, occupying negligible volume
.as an object radiates energy at a given rate, it also - Answer-absorbs radiation
if it didn't the object would eventually radiate all its energy and its temperature would
reach absolute zero
the energy an object absorbs comes from its environment, which consists of other
bodies that radiate energy
if an object is at a temperature T and its surroundings at a temperature T0, the net
energy gained or lost each second by the object as a result of radiation is
Pnet = εσA(T^4 - T0^4)
, .assumptions of kinetic theory of gases - Answer-the number of molecules in the gas is
large, and the average separation between them is large compared with their
dimensions
the molecules obey Newton's laws of motion, but as a whole they move randomly
the molecules interact only through short-range forces during elastic collisions
the molecules make elastic collisions with the walls
all molecules in the gas are identical
.average kinetic energy per molecule - Answer-mv^2/2 = 3kbT/2
.Avogardo's number - Answer-Na = 6.02 X 10^23 particles/mole
.Avogardo's number and the definition of a mole are fundamental to chemistry and
related branch of physics - Answer-the number of moles of a substance is related to its
mass by the expression
n = m/molar mass
where the molar mass of the substance is defined as the mass of one mole of that
substance, usually expressed in grams per mole
.Avogardo's number was chosen so that - Answer-the mass in grams of one Avogardo's
number number of an element is numerically the same as the mass of one atom of the
element, expressed in atomic mass units (u)
this relationship is very convenient
looking at the periodic table of the elements, we find that carbon has an atomic mass of
12 u, so 12 g of carbon consists of exactly 6.02 X 10^23 atoms of carbon
the atomic mass of oxygen is 16 u, so in 16 g of oxygen there are again 6.02 X 10^23
atoms of oxygen
the same holds true for molecules
the molecular mass of hydrogen, H2, is 2 u, and there is an Avogardo's number of
molecules in 2 g of molecular hydrogen
.because the size of a Celsius degree is the same as a kelvin, a temperature difference
of 5°C is equal to a - Answer-temperature difference of 5 K
the two scales differ only in the choice of zero point
the ice point (273.15 K) corresponds to 0.00°C, and the steam point (373.15 K) is
equivalent to 100.00°C
.because there are 6.02 X 10^23 particles in one mole of any element - Answer-the
mass per atom for a given element is
m = molar mass/Na
.Boltzmann's constant - Answer-kb = R/Na = 1.38 X 10^-23J/K
.British thermal unit (Btu) - Answer-the energy required to raise the temperature of 1 lb
of water from 63°F to 64°F
