chemical thermodynamics and the thermodynamic foundations of life
DESCRIPTION
Chemical Thermodynamics And the Thermodynamic Foundations of Life. Engines. capitalize on the fact that heat flows from hot to cold convert some heat to work. not all energy can be converted to work, some heat is always lost A cyclic process Takes you back to same P, T, U U = Q - W = 0 - PowerPoint PPT PresentationTRANSCRIPT
Chemical ThermodynamicsAnd the Thermodynamic Foundations of Life
not all energy can be converted to work, some heat is always lost
A cyclic process • Takes you back to same P, T, U• U = Q - W = 0 • Q = W
Here, Q = QC + QH
Efficiency e = W / QH
1. capitalize on the fact that heat flows from hot to cold2. convert some heat to work.
Engines
How much energy is available for work?
“Free energy”
Gibbs free energy G
First law of thermo dE = dQ - dW
adding in entropy and P-V work dE = T dS - P dV
Define Gibbs free energy G = E + PV - TS
a derivative & some algebra dG = V dP - S dT
Same as U
At equilibrium,
Therefore, what is dG?
dG = 0(now think min, max, slope, entropy)
dG = V dP - S dT
G does the opposite of what entropy does:G is minimized
P and T stay constant.
G = how much useful work can be done (not just heat released) at constant T and P.
At equilibrium, no more work can be done.
We can think of a cell as an engine…
dG = V dP - S dT + dN
Chemistry!
= chemical potential = how G depends on N (# molecules)
dN = the sum of all dN for all chemical species involved in a reaction
Example: N2 + 3 H2 --> 2 NH3 .
dN = 1 N2 + 3 H2 - 2 NH3
At equilibrium, G is at a minimum, so dN = 0
Chemical reactions proceed in a certain direction depending on T and P.
How does it “know” which way to go?
Rate = forward - reverse reaction rates
Rate constant k: Experimental:
A catalyst lowers the activation energy