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Chapter 4

BI110 Chapter Notes - Chapter 4: Exergonic Reaction, Metabolic Pathway, Chemical Equilibrium

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Diane Williams

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4.1 Energy and the Laws of Thermodynamics
Energy can be defined as the capacity to do work
4.1a Energy Exists in Different Forms and States
energy can exist in many different forms, including heat, chemical, electrical, mechanical energy
and electromagnetic radiation (visible, infrared and ultraviolet light)
Kinetic energy is the energy possessed by an object because it is in motion
Potential energy is stored energy; the energy of an object because of its location or chemical
4.1b The Laws of Thermodynamics Describe the Energy Flow in Natural Systems
Thermodynamics is the study of energy and its transformations
An isolated system is one that does not exchange matter or energy with it’s surroundings (ie.
thermos bottle)
a closed system can exchange energy but not matter with its surroundings (ie. Earth)
an open system can exchange energy and matter freely between the system and the surroundings
(ie. living organisms)
4.1c The First Law of Thermodynamics
first law of thermodynamics, energy can be transformed from one form into another or transferred
fro one place to another, but it cannot be created or destroyed (AKA Principle of the Conservations of
4.1d The Second Law of Thermodynamics
each time energy is transformed from one form into another, some of the energy is lost and
unavailable to do work, it is never 100% efficient
entropy is the disorder or randomness of the universe, increased by the inefficient energy lost in
second law of thermodynamics states that the total disorder (entropy) of a system and its
surroundings always increases
systems will move spontaneously toward arrangements with greater entropy
4.1e Life and the Second Law of Thermodynamics
it takes energy to maintain low entropy
living things bring in energy and matter and use them to generate order out of disorder
4.2 Free Energy and Spontaneous Reactions
spontaneous reactions are chemical reactions that will occur without the input of energy, means
only that it will occur, not necessarily a fast reaction

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4.2a Energy Content and Entropy Contribute to Making a Reaction Spontaneous
1. Reactions tend to be spontaneous if the products have less potential energy than the reactants
enthalpy is the amount of potential energy in a system (H)
endothermic reactions absorb energy, those that release energy are exothermic
2. Reactions tend to be spontaneous when the products are less ordered than the reactants
entropy (free energy) of the products is greater than the entropy of the reactants. High potential
energy, low disorder --> low potential energy, high disorder
4.2b The Change in Free Energy Indicates Whether a Reaction is Spontaneous
free energy is the portion of a system’s energy that is available to do work (G)
In living organisms, free energy accomplishes the chemical and physical work involved in activities
such as the synthesis of molecules, movement and reproduction
Change in free energy: G = H -T SΔ Δ Δ
Δfree energy = Δenthalpy - (absolute temp)(Δchange in entropy)
where H is the change in enthalpy, S is the change in the entropy of the system of the courseΔ Δ
of the reaction and T is the absolute temperature in kelvin
the equation says that the free energy change as a system goes from initial to final states is the sum
of the changes in energy content and entropy
For a reaction to be spontaneous, the G Δmust be negative
for all chemical and physical processes, there is an interplay of both entropy and enthalpy to
determine whether it will occur spontaneously
G represents the difference between the free energy of the final state compared with the initialΔ
state and thus - G indicates that the products have Δless free energy than the reactants
high free energy = less stable, thus wants to be more stable
4.2c Life and Equilibrium
equilibrium is another term for maximum stablility
point of chemical equilibrium is a state in which the reaction does not stop but rather a state in
which the rate of forward reaction equals the rate of backwards reaction. NOT NECESSARILY
lowest point and max stability at equilibrium, NO free energy ( G is 0)Δ
to move away from the equilibrium point requires free energy and thus will not be spontaneous
the G of life is Δalways negative as organisms constantly take in energy-rich molecules and use
them to do work
organisms reach equilibrium (ΔG = 0) only when they die
4.2d Metabolic Pathways Consist of Exergonic and Endergonic Reactions
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