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.

3. When the molecule strikes the rocks below, its kinetic energy is converted to thermal, mechanical, and sound energy.

1. A water molecule sitting at the top of a waterfall has a defined amount of potentialenergy, Ep.

2. As the molecule falls, this stored energy is converted tokinetic energy, Ek.

Mechanical energy

Heat Sound

Ep (lower)

Ek

Ep (higher)ENERGY TRANSFORMATION IN A WATERFALL

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 Products

AB + CD AC + BD

When the forward and back reactions occur at the same rate, the system is stable and is called a chemical equilibrium

Example of an exergonic reaction: Burning methane

H

H

CH H CO OO O OH H Energy

2 WaterCarbon dioxide

OxygenMethane

Exergonic reactions release energy and occur spontaneously

High-energy photon High-energy photon

HH

H O O

OO C

C

Endergonic reactions require the addition of energy

Energy + H2 H + H Energy + CO2 CO + 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)