### Gibb`s Free Energy PPT

```Gibbs Free Energy
Energy and the States of Energy
Energy is the ability to
do work.
Two states of energy
1. Potential energy −
Stored energy
2. Kinetic energy −
Active energy or the
energy of movement.
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First Law of Thermodynamics
Energy cannot be created or destroyed only
transformed from one form to another.
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nd
2
Law of Thermodynamics
As energy conversions occur, some of the usable
energy is converted into unusable energy in the
form of heat energy (more entropy). Heat energy
can do work but only if there is a heat gradient.
25% Efficient
75% Unusable Energy
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Free Energy
Represents an energy transformation
Free energy is energy that is available to do work.
The amount of free energy in a system is always
lower than the total energy of the system.
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nd
2
Law of Thermodynamics
• Over time, in a closed
system, there is a
decrease in the amount
of free energy available
to do work, and, as a
result, the entropy of the
system will continue to
increase. This will
continue until the
Over time, entropy has
system exhausts its
increased with respect to
the building in this picture. supply of free energy.
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Free Energy
• As free energy decreases, there is an increase
in the disorder of the system. It takes free
energy to maintain a system’s order. Entropy is
a measure of that disorder.
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Living Organisms Obey the 1st and 2nd Law
of Thermodynamics
• All living organisms
need a source of
free energy to live,
grow, and reproduce.
Most autotrophs rely
energy. Heterotrophs
rely on the food they
consume.
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Energy and Chemical Bonds
• During a chemical reaction, bonds are broken
and bonds are remade. The chemical energy of
the reactants will be different from the chemical
energy of the products.
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Energy of Activation
• If you mix two moles of hydrogen gas H2 with
one mole of oxygen gas-nothing happens.
• If you add a spark to the container, the following
reaction occurs. KABOOM
• 2H2 + O2 →2 H2O DG=−58 kcal/mole
In order for water to be
produced H2 must become 2H
and the O2 must become 2O
as this frees up the electrons
tied up in covalent bonds, to
form chemical bonds forming
water, H2O.
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Energy of Activation
The energy used to
break the bonds in
the reactants so
they can be
reformed in the
products is called
the energy of
activation.
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Enthalpy and Bond Energies
Consider the combustion of methane gas. It does release heat
energy.
CH4 + 2 O2→ CO2 + 2 H2O
Bonds Broke (energy absorbed)
4 C−H 4 × 98
= 392 kcal/mole
2 C=O 2 × 187 = 374 kcal/mole
2 O=O 2 × 116 = 232 kcal/mole
4 O−H 4 × 110 =440 kcal/mole
Total energy Reactants
624 kcal/mole
Total energy products
814 kcal/mole
Net energy (enthalpy ΔH)= 624 −814 = −190 kcal/mole of heat
energy released
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Exothermic and Endothermic Reactions
• A decrease in enthalpy (DH) is said to be
an exothermic reaction and has a –DH .
Burning of wood is exothermic
• An increase in enthalpy (DH) is said to be
an endothermic reaction and had a + DH.
Photosynthesis overall is endothermic.
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Exergonic and Endergonic Reactions
Changes in energy can be calculated as
DG = Gfinal – Ginitial
OR
DG = DH – TDS
Exergonic reaction is one that releases free
energy to its surroundings.
Endergonic reaction is one that absorbs free
energy from its surroundings.
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Energy and ATP
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Energy and ATP
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Coupling Reactions
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Coupling Reactions
Photosynthesis is overall is
endergonic.
6H2O + 6O2 → 6C6H12O6 + 6O2
DG=+686 kcal/mol
Energy is coming from the sun.
Cell Respiration is overall
exergonic.
6C6H12O6 + 6O2 → 6H2O + 6O2
DG=−686 kcal/mol
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Coupling Reactions
Metabolism is the sum
total of all the
biochemical reactions
occurring in a cell.
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Coupling Reactions
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Spontaneous Reactions
Spontaneous reactions are reactions that are
energetically favorable and occur without outside energy.
Systems in general move from a high energy state to low
energy state. In general exothermic reactions are
spontaneous -- but not always.
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Spontaneous Reactions
• Consider a beaker of water. Over time it will
evaporate. In order for the water molecules to
have enough energy to escape and become a
gas, energy must be absorbed from the
surrounding environment. This is an
endothermic reaction BUT it is also a
spontaneous reaction.
If systems go from a high energy
state to a lower energy state, there
must be ANOTHER factor in
determining Gibbs free energy. That
second factor is entropy or
randomization.
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How Reactions Can Be Spontaneous
or Exergonic
• Changes in free energy can be quantified by the equation
DG= DH−TDS
• G=free energy, H=enthalpy, T=absolute temperature (K),
S=entropy
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Exergonic and Endergonic Reactions
Changes in energy can be calculated as
DG = Gfinal – Ginitial
OR
DG = DH – TDS
Exergonic reaction is one that releases free
energy to its surroundings.
Endergonic reaction is one that absorbs free
energy from its surroundings.
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Chemical Reactions Result in D G
• (a) DG < 0 or - DG
(b) DG > 0 or +DG
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Effects of Changes in Entropy and Its Effect
on the Free Energy of a System
Both reactions are spontaneous and free energy
decreases.
CaCl2(S) + H2O(aq) → Ca2+(aq) + 2Cl−(aq)
Exergonic and exothermic
-DG = - DH + T - DS
Exergonic but endothermic!!!
NH4Cl(s) + H2O(aq) → NH4+(aq) + Cl−(aq)
- DG = +DH + T- DS The change in entropy is greater
than the change in enthalpy.
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Examples of Decreasing Amounts of
Free Energy
• In general, energy transfers favor going from a
higher energy state to a lower energy state.
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Changes in Entropy and Its Effect on
Membranes
• Changes in entropy affect living systems in other
ways other beyond the molecular level.
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Entropy also Affects the Circulatory System
• The differences in the concentration of oxygen and
carbon dioxide is the driving force moving these gases
from the lungs to various body cells. Again these are
spontaneous reactions.
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Entropy also Affects the Excretory System
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Entropy also Affects Ecosystems
• The 2nd law of thermodynamics is, in part, responsible for
the declining amount of free energy as it is transferred from
one trophic level to next trophic level.
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