The body provides us with an excellent indication that many thermodynamic processes are
irreversible . An irreversible process can go in one direction but not the reverse, under a given set of conditions. For example, although body fat can be converted to do work and produce heat transfer, work done on the body and heat transfer into it cannot be converted to body fat. Otherwise, we could skip lunch by sunning ourselves or by walking down stairs. Another example of an irreversible thermodynamic process is photosynthesis. This process is the intake of one form of energy—light—by plants and its conversion to chemical potential energy. Both applications of the first law of thermodynamics are illustrated in
[link] . One great advantage of conservation laws such as the first law of thermodynamics is that they accurately describe the beginning and ending points of complex processes, such as metabolism and photosynthesis, without regard to the complications in between.
[link] presents a summary of terms relevant to the first law of thermodynamics.
Summary of terms for the first law of thermodynamics,
ΔU=Q−W
Term
Definition
Internal energy—the sum of the kinetic and potential energies of a system’s atoms and molecules. Can be divided into many subcategories, such as thermal and chemical energy. Depends only on the state of a system (such as its
,
, and
), not on how the energy entered the system. Change in internal energy is path independent.
Heat—energy transferred because of a temperature difference. Characterized by random molecular motion. Highly dependent on path.
entering a system is positive.
Work—energy transferred by a force moving through a distance. An organized, orderly process. Path dependent.
done by a system (either against an external force or to increase the volume of the system) is positive.
Section summary
The first law of thermodynamics is given as
, where
is the change in internal energy of a system,
is the net heat transfer (the sum of all heat transfer into and out of the system), and
is the net work done (the sum of all work done on or by the system).
Both
and
are energy in transit; only
represents an independent quantity capable of being stored.
The internal energy
of a system depends only on the state of the system and not how it reached that state.
Metabolism of living organisms, and photosynthesis of plants, are specialized types of heat transfer, doing work, and internal energy of systems.
Conceptual questions
Describe the photo of the tea kettle at the beginning of this section in terms of heat transfer, work done, and internal energy. How is heat being transferred? What is the work done and what is doing it? How does the kettle maintain its internal energy?
the transfer of energy by a force that causes an object to be displaced; the product of the component of the force in the direction of the displacement and the magnitude of the displacement
A wave is described by the function D(x,t)=(1.6cm) sin[(1.2cm^-1(x+6.8cm/st] what are:a.Amplitude b. wavelength c. wave number d. frequency e. period f. velocity of speed.
A body is projected upward at an angle 45° 18minutes with the horizontal with an initial speed of 40km per second. In hoe many seconds will the body reach the ground then how far from the point of projection will it strike. At what angle will the horizontal will strike
Suppose hydrogen and oxygen are diffusing through air. A small amount of each is released simultaneously. How much time passes before the hydrogen is 1.00 s ahead of the oxygen? Such differences in arrival times are used as an analytical tool in gas chromatography.
the science concerned with describing the interactions of energy, matter, space, and time; it is especially interested in what fundamental mechanisms underlie every phenomenon