chapter 4.docx

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Published on 17 Apr 2013
School
WLU
Department
Biology
Course
BI110
Professor
Page:
of 20
Energy is defined as the capacity to do useful work.
Kinetic energy: energy in motion
Potential energy: stored energy
Energy may converted readily from one form to another
Thermodynamics
Study of energy and its transformations
o Energy is 2 types: kinetic and potential
1st law: energy can be transformed but not created or
destroyed
2nd law: total disorder of a system and its surroundings
always increases
o Entropy is the measure of disorder
Isolated neither energy nor matter is exchanged (thermos)
Closed energy is exchanged but matter isn’t (earth)
Open both energy and matter are exchanged (organism)
Why do we need to eat?
Average person consumes 1500 kcal/day
Significant portion of this energy is used to maintain order in
our cells
We eat food to maintain low entropy!
Thermodynamics in the living cell
energy content and entropy contribute to making a reaction
spontaneous
spontaneous reactions -> occur without an input of energy
from the surroundings
reactions tend to be spontaneous if products have less
potential energy than reactants
o enthalpy (H): Potential energy in a system
reactions tend to be spontaneous when products are less
ordered than reactants
o entropy (S): Amount or randomness or disorder
Exergonic reactions are spontaneous
Potential Energy of Products & Reactants
Endothermic reactions: reactions that absorb energy ->
products have more potential energy than reactions
Exothermic reactions: reactions that release energy ->
products have less potential energy than the reactants
o Example: burning of natural gas (methane)
CH4 + 2O2 CO2 + 2H2O
A Spontaneous Endothermic Reactions
How can melting of ice be a spontaneous reactions if it is
endothermic?
Melting ice increases entropy
Phases changes result in an increase in entropy
o Solid liquid gas
Free Energy (ΔG)
ΔG = ΔT TΔS
Δ(delta) = change (final state initial state)
ΔG = change in free energy
ΔH = change in enthalpy
T = absolute temperature (degree kelvin)
ΔS = change in entropy
as a reactions goes to completion, it is influenced by two factors:
changes in energy content: ΔH
changes in entropy: ΔS
For a spontaneous reaction, ΔG < 0
Chemical Reactions and Equilibrium
Equilibrium is maximum stability
Equilibrium point is reached when reactants are converted to
products and products are converted back to reactants at
equal rates ΔG = 0

Document Summary

Energy is defined as the capacity to do useful work. Energy may converted readily from one form to another. Study of energy and its transformations: energy is 2 types: kinetic and potential. 1st law: energy can be transformed but not created or destroyed. 2nd law: total disorder of a system and its surroundings always increases: entropy is the measure of disorder. Isolated neither energy nor matter is exchanged (thermos) Closed energy is exchanged but matter isn"t (earth) Open both energy and matter are exchanged (organism) Significant portion of this energy is used to maintain order in our cells. We eat food to maintain low entropy! Thermodynamics in the living cell energy content and entropy contribute to making a reaction spontaneous. Spontaneous reactions -> occur without an input of energy from the surroundings. Reactions tend to be spontaneous if products have less potential energy than reactants: enthalpy (h): potential energy in a system.