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Physics 5D Fall 2008
Due at 2:00pm on Tuesday, November 18, 2008
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Isobaric, Isochoric, Isothermal, and Adiabatic Processes
Isobaric, isochoric, isothermal, and adiabatic processes on an ideal gas are examined using pV diagrams.
Questions are posed about heat, work, and how they explain internal energy change using the first law of thermodynamics.
To recognize various types of processes on
diagrams and to understand the relationship between
diagram geometry and the quantities
The first law of thermodynamics is an expression of conservation of energy. This law states that changes in the internal energy of
can be explained in terms of energy transfer into or out of the system in the form of heat
this problem, we will write the first law of thermodynamics as
Here "in" means that energy is being transferred into the system, thereby raising its internal energy, and "out" means that energy
is leaving the system, thereby reducing its internal energy. You will determine the sizes of these energy transfers and classify
their effect on the system as
Consider a system consisting of an ideal gas confined within a container, one wall of which is a movable piston. Energy can be
added to the gas in the form of heat by applying a flame to the outside of the container. Conversely, energy can also be
removed from the gas in the form of heat by immersing the container in ice water. Energy can be added to the system in the
form of work by pushing the piston in, thereby compressing the gas. Conversely, if the gas pushes the piston out, thereby
pushing some atmosphere aside, the internal energy of the gas is reduced by the amount of work done.
The internal energy of an ideal gas is directly proportional to its absolute temperature
. An ideal gas also obeys the ideal gas
so the absolute temperature
is directly proportional to the product of the absolute pressure
and the volume
denotes the amount of gas in moles, which is a constant because the gas is confined, and
is the universal gas constant.
diagram is a convenient way to track the pressure and
volume of a system. Energy transfers by heat and/or work are
associated with processes, which are lines or curves on the
diagram taking the system from one state (i.e., one point on the
diagram) to another. Work corresponds geometrically to the area
under the curve on a
diagram. If the volume increases (i.e.,
the system expands) the work will be classified as an energy
output from the system.