BIOL130 Lecture Notes - Lecture 7: Bond Energy, Endergonic Reaction, Thermodynamics

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1 Aug 2016
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BIOL 130 – Week Three Notes
What is thermodynamics?
-Thermodynamics = the relationship between forms of energy and heat; the
interconversion between forms of energy
What are the 2 laws of thermodynamics?
1. Energy can be transferred and transformed, it cannot be created nor
destroyed
2. Energy tends to spontaneously disperse – from being localized/ordered to
becoming spread out/disordered
o Entropy = disorder
What is energy?
-Energy = the capacity to do work
oTo move matter against opposing forces
oTo rearrange matter
What are the 2 types of energy that we are specifically looking at?
-Kinetic Energy (EK) – the energy of motion, heat
-Potential Energy (EP) – stored energy as a result of…
oLocation – Ex. ball at top of hill, water behind dam
oStructure – Ex. arrangement of atoms within a molecule
What is the relationship between energy and chemical bonds?
-Chemical bonds contain stored (potential) energy
-Chemical reactions can therefore provide a source of useful cellular energy
What role do electrons and chemical bonds play in regards to energy?
-Electrons participating in chemical bonds are a source of potential energy
-Bond formation is favorable
-Breaking bonds gives cell source of potential energy because we’re not just
breaking bonds, we are remaking them as well
-The formation of some types of new bonds can free more energy than
required to break the old bond
oTherefore, breaking these types of bonds  releases energy
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What do chemical reactions generally entail?
-The making and breaking of chemical bonds
oThe shifting of atoms from one molecule to another
-Energy is released – available for use or lost as heat
When are chemical reactions considered to be “spontaneous”?
-Chemical reactions are ‘spontaneous’ if they occur on their own, without
external input (such as added energy)
What are the 2 main types of reactions in regards to energy?
-Exergonic Reactions:
oOccur spontaneously
oReactants have more potential energy than products  net release of
energy
-Endergonic Reactions:
oDo not occur spontaneously
oReactants contain less energy than products  net input of energy
required
What is the concept of Gibbs Free Energy (G)?
-Gibbs Free Energy (G) = A measurement of the "useful” work obtainable
from a system at a constant temperature and pressure; quantative way of
determining how much energy is available
oΔG = free energy difference ; ΔG = Gproducts – Greactants
If < 0 (-ve value), reactants have more potential energy  =
Exergonic
If > 0 (+ve value), products have more potential energy 
=Endergonic
oΔG° = standard free energy to compare different reactions
The magnitude of ΔG° informs us on the equilibrium position in
a reaction
Due to the additive nature of ΔG° we have the thermodynamic
basis for how cells are able to carry out the synthesis of
complex, energy-rich molecules
Independent of concentration
Depends only on intrinsic characteristics of molecules
“Ideal conditions” - concentration of all reactants = 1M @ pH 7
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