The Laws of Thermodynamics
Unit 3: Bioenergetics
Honors Biology
Monkemeier
Energy Conversions
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All of the activities of living organisms involve
energy changes aka energy conversions.
Two universal laws govern all energy
conversions (aka energy changes) in the
universe.
The two laws are known as the Laws of
Thermodynamics.
The First Law of Thermodynamics
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Energy can be changed from one form to
another, but it cannot be created or
destroyed. The total amount of energy and
matter in the Universe remains constant,
merely changing from one form to another.
The First Law of Thermodynamics
(Conservation) states that energy is always
conserved, it cannot be created or
destroyed.
First Law of Thermodynamics
Energy Flow Through Living Systems
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Living Systems require a constant supply of
energy.
In living systems chemical potential energy
stored in some molecules can be shifted to
other molecules and stored in different
chemical bonds, or it can be converted into
other forms, such as kinetic energy, light, or
electricity.
Heat
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During each energy conversion, some of the
energy dissipates into the environment as
HEAT, which is a measure of the random
motion of molecules (and therefore a
measure of one form of kinetic energy).
Living organisms can not harness heat to
perform work because cells are too small to
create a heat differential.
Energy Flow through Living Systems
 Energy
continuously flows through
the biological world in one
direction, with new energy from the
SUN continuously enterring the
system to replace the energy
dissipated as heat.
HEAT
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Heat can only be harnessed to perform work when
there is a heat gradient.
Heat gradient = temperature difference between two
areas.
Cells are too small to maintain significant internal
temperature differences, so heat energy is incapable
of performing the work of cells.
Cells MUST RELY UPON CHEMICAL ENERGY!
First Law of Thermodynamics and
HEAT!
 Although
the total amount of
energy in the universe remains
constant, the energy available to
do work decreases as more of it
progressively dissipates as heat.
Second Law of Thermodynamics
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The Second Law of Thermodynamics
states that "in all energy exchanges, if no
energy enters or leaves the system, the
potential energy of the state will always be
less than that of the initial state." This is also
commonly referred to as entropy.
Second Law of Thermodynamics
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The second law is based on human experience. It
doesn’t come from complicated theory and
equations. So, think of these experiences that you
have had:
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A rock will fall if you lift it up and then let go.
Hot frying pans cool down when taken off the stove.
Iron rusts (oxidizes) in the air.
Air in a high-pressure tire shoots out from even a small hole
in its side to the lower pressure atmosphere.
Ice cubes melt in a warm room.
Second Law of Thermodynamics
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Energy spontaneously disperses from being localized to
becoming spread out if it is not hindered from doing so.
A watch-spring-driven watch will run until the potential energy in
the spring is converted, and not again until energy is reapplied
to the spring to rewind it.
A car that has run out of gas will not run again until you walk 10
miles to a gas station and refuel the car.
Once the potential energy locked in carbohydrates is converted
into kinetic energy (energy in use or motion), the organism will
get no more until energy is input again.
In the process of energy transfer, some energy will dissipate as
heat.
Second Law of Thermodynamics = Law
of Entropy
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Entropy is a measure of disorder: cells are
NOT disordered and so have low entropy.
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The flow of energy maintains order and life.
Entropy wins when organisms cease to take
in energy and die.
2nd Law = Law of Entropy
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The Second Law of Thermodynamics states
that the disorder, or entropy, in the universe
is increasing. This also means that
conversions of energy from one form to
another are inefficient, with some energy
being lost to cells as HEAT.
(REMINDER the word LOST means that
organisms can not harness HEAT to do
work.)
Second Law of Thermodynamics
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The Second law of
Thermodynamics predicts
that matter and energy tend
to become increasingly
disorganized in this universe.
The law says that disorder is
more probable than order
and that to maintain order, it
is necessary to expend
energy. The Second law
implies that there can be no
such thing as a perfectly
insulated container and that
no transfer of energy can
occur without some energy
loss.
Second Law of Thermodynamics
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The Second Law of
Thermodynamics Explains
this Pyramid of Energy.
Moving from producers
towards carnivores there is
less useful energy available
because as energy
transforms from one level to
the next some of it is
converted into HEAT which
is a useless form of energy
to organisms.
Second Law – Final Thoughts
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In general, energy transformations proceed
spontaneously to convert matter from a more
ordered, less stable form to a less ordered, but
more stable form.
The Second Law is often called “time’s arrow”.
When the universe was formed it held all of the
potential energy it will ever have. It has become
progressively more disordered since, with every
energy exchange increasing the amount of entropy
(disorder)
Laws of Thermodynamics and
FREE ENERGY
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Free energy is the energy available to do work in any
system.
Free energy is important to cells (organisms) and
cells store and release free energy using the ATP
molecule.
The chemical reactions inside of cells can be
explained using the Laws of Thermodynamics.
The chemical reactions (inside and outside of cells)
can be predicted based on free energy changes.
What’s Next?
 The
next PPT will focus upon
predicting chemical reactions and
free energy changes!
 The words exergonic, endergonic,
activation energy will all come
back! 