Thermodynamics Flashcards
coupling reactions
couple energetically unfavourable reaction with favourable
free energy changes are additive
isolated system
cannot exchange matter or energy with its surroundings
closed system
can exchange energy but not matter with its surroundings by heat or work
open system
can exchange both matter and energy with surroundings
all living systems
1st law thermodynamics
energy cannot be created or destroyed
state function
state function
property that is independent of the history of the system
energy change is independent of pathway taken. depends only on initial and final states of the system
enthalpy change
heat energy change at a constant pressure
state function
change in internal energy + volume
2nd law thermodynamics
the combined entropy of system and surroundings must increase in any spontaneous process
entropy
state function
measures degree of disorder of a system
properties of a system at equilibrium at a global scale
temperature, total energy, entropy all stable
what happens when you perturb an equilibrium system
global properties relax to new equilibrium values
gibbs free energy
state function incorporating both energy and entropy changes
energy available to do work
what happens when a system is far from equilibrium
tends to move to equilibrium in an irreversible process
what happens to a system in equilibrium
change in G=0
process is reversible
can be made to go in either direction by small changes in conditions
why is maximum equilibrium unstable
gibbs free at a local maximum
small deviation to system will drive it away from equilibrium
why is free energy an extensive property
it depends on the amount of material (moles) in the system
endergonic process
delta G > 0
forward process energetically unfavourable
reverse spontaneous
exergonic process
delta G < 0
forward process energetically favourable and occurs spontaneously
how do organisms make a specific reaction proceed in the direction required
altering concentrations
coupling reactions
entropy equation
S=klnW
k=boltzman constant, 1.38 x10^-23
W= number of microstates
equation for gibbs free involving standard free energy change
delta G = delta G standard + RT ln [C]^c [D]^d / [A]^a [B]^b
mass action ratio
[products] / [reactants] = Keq
standard conditions
1M
298K
1atm
delta G standard equation with Keq
delta G standard = -RT lnKeq
if delta G standard is less than 0, what does this mean for Keq?
> 1
if delta G standard = 0, what does this mean for Keq?
=1
if delta G standard is greater than 0, what does this mean for Keq?
<1
thermodynamic basis of metabolic pathways
coupling of an endergonic reaction to an exergonic reaction with a more negative delta G, exploits fact that free energies are additive
properties of ATP that make it have negative delta G
relief of electrostatic repulsion when terminal phosphate bond hydrolysed so its hydrolysis is thermodynamically favoured.
ionisation of ADP releases protons
ATP is thermodynamically unstable but kinetically stable so has high activation energy to hydrolyse.
