Download Lecture 9: Energy

Energy
The ultimate
source of all
energy on Earth
The Addition of Energy was
important in early chemical
evolution
• Energy = the capacity to do work
– Potential energy = stored energy
– Kinetic energy = energy of motion
– Other types of energy = thermal, sound,
mechanical, light, etc.
ENERGY
TRANSFORMATION
IN A WATERFALL
Ep (higher)
1. A water molecule sitting
at the top of a waterfall has a
defined amount of potential
energy, Ep.
Ek
2. As the molecule falls, this
stored energy is converted to
kinetic energy, Ek.
Heat Sound
Mechanical
energy
Ep (lower)
3. When the molecule
strikes the rocks below,
its kinetic energy is
converted to thermal,
mechanical, and sound
energy.
Newton’s First Law of
Thermodynamics
• Energy is never created or destroyed, it
is converted from one form to another
• The total amount of energy in a closed
system remains the same
Newton’s Second Law of
Thermodynamics
• In a closed system, energy will
transformation will always occur so that
the entropy of the system will increase
• Entropy = random, useless energy that
cannot do work, disorder, randomness
Newton’s Second Law of
Thermodynamics
• Living organisms are highly ordered
Spontaneous changes within a system will occur to increase
the entropy and free energy in a system
G = the quantity of energy in a system that can perform work
∆G = G final state - G starting state
How do chemical reactions occur?
• Chemical reactions = the formation and breaking of
chemical bonds:
Reactant
+
Reactant
AB
+
CD


Products
AC + BD
When the forward and back reactions occur at the same
rate, the system is stable and is called a chemical
equilibrium
Exergonic reactions release
energy and occur spontaneously
Example of an exergonic reaction: Burning methane
H
H
C
H
O
O
O
C
O
H
O
H
H
Methane
Oxygen
Carbon
dioxide
2 Water
Energy
Endergonic reactions require the
addition of energy
Energy + H2  H + H
Energy + CO2  CO + O
High-energy photon
High-energy photon
H
H
H
O
O
C
C
O
O
Energy changes in exergonic and
endergonic reactions
Free energy in chemical reactions
• The amount of free energy in a system
depends on the entropy, temperature of
the system:
G = H - TS
• The change in energy in a system is:
∆G = ∆H - T ∆GS
To do work and power endergonic reactions,
cells use ATP
Coupling of exergonic and endergonic reactions
ATP is regenerated continuously
(cell respiration)