Chapter 5: Free Energy and Chemical Thermodynamics

Outline

Free Energy as Available Work

Free Energy as Force toward Equilibrium

Chapter 5: Free Energy and Chemical Thermodynamics

Applications of the laws of thermodynamics Part 1: Chemical reactions

X Bai

SDSMT, Physics

Fall 2014

X Bai

Chapter 5: Free Energy and Chemical Thermodynamics

Outline

Free Energy as Available Work

Free Energy as Force toward Equilibrium

1 Free Energy as Available Work Basic tools Electrolysis, Fuel Cells, Batteries Thermodynamic Identities revisit: In chemical reactions

2 Free Energy as Force toward Equilibrium Non-isolated system

X Bai

Chapter 5: Free Energy and Chemical Thermodynamics

Outline

Basic tools

Free Energy as Available Work

Free Energy as Force toward Equilibrium

What are the typical thermal conditions for chemical reactions and

other transformations of matter?

Electrolysis:

H2O

H2

+

1 2

O2

Energy: may vary (reactions may release or absorb heat),

chemical reactions happen in non-isolated system

Volume: often not fixed, new substances can be created

Number of particles: often change in reactions

Pressure: often fixed, equal to the environment

Temperature: equal to the environment, approximately fixed

We are looking for Tools for fixed T and P !!!

X Bai

Chapter 5: Free Energy and Chemical Thermodynamics

Outline

Basic tools

Free Energy as Available Work

Free Energy as Force toward Equilibrium

To describe the energy budget:

1. Enthalpy :

H U + PV

(1)

H: The total energy to create the system AND let it stay

in the environment with pressure P - Need the work.

2. Helmholtz Free Energy :

F U - TS

(2)

U: The total energy to create the system;

TS = Q: The heat from the environment, with T fixed.

F : energy needed in the format of work if the

system is created from nothing.

3. Gibbs Free Energy :

G U - TS + PV = F + PV = H - TS

(3)

PV is the work done under the constant pressure P.

X Bai

Chapter 5: Free Energy and Chemical Thermodynamics

Outline

Free Energy as Available Work

H, G, Q=TS, W=PV: An example

Free Energy as Force toward Equilibrium

Nothing Rabbit

Left: in an environment with pressure P (without heat exchange with the environment)

W = PV : push out a volume for the rabbit H = Urabbit + PV : Required entire energy, the Enthalpy.

Right: in chemical reactions that can have heat exchange with the environment. Q = TS: can flow in as heat from the environment. G = H - TS: Energy the magician needs to provide.

X Bai

Chapter 5: Free Energy and Chemical Thermodynamics

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