chemical thermodynamics and the thermodynamic foundations of life

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