thermodynamics
Download
Skip this Video
Download Presentation
Thermodynamics

Loading in 2 Seconds...

play fullscreen
1 / 19

Thermodynamics - PowerPoint PPT Presentation


  • 141 Views
  • Uploaded on

Production of quicklime. Thermodynamics. Liquid benzene. ⇅. Solid benzene. Chapter 19. CaCO 3 (s) ⇌ CaO + CO 2. Gibbs Energy. For a constant-pressure & constant temperature process:. Gibbs energy (G). D G = D H sys - T D S sys.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Thermodynamics' - chava-salazar


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
thermodynamics
Production of quicklime

Thermodynamics

Liquid benzene

Solid benzene

Chapter 19

CaCO3 (s) ⇌ CaO + CO2

slide2
Gibbs Energy

For a constant-pressure & constant temperature process:

Gibbs energy (G)

DG = DHsys - TDSsys

DG < 0 The reaction is spontaneous in the forward direction

DG > 0 The reaction is nonspontaneous as written. The

reaction is spontaneous in the reverse direction

DG = 0 The reaction is at equilibrium

slide5
Standard free-energy of reaction (DGorxn)≡ free-energy change for a reaction when it occurs under standard-state conditions.

aA + bB cC + dD

-

mDG° (reactants)

S

S

=

f

DG°

rxn

nDG° (products)

f

  • Standard free energy of formation (DG°)
  • Free-energy change that occurs
  • when 1 mole of the compound
  • is formed from its elements
  • in their standard states.

f

slide6
What’s “Free” About Gibbs Energy?
  • ΔG ≡ the theoretical maximum amount of work that can be
  • done by the system on the surroundings at constant P and T
  • ΔG = − wmax

Fig 19.19 Energy Conversion

slide7
What’s “free” about the Gibbs energy?
  • “Free” does not imply that the energy has no cost
  • For a constant-temperature process, “free energy”
  • is the amount available to do work
  • e.g., Human metabolism converts glucose to
  • CO2 and H2O with a ΔG° = -2880 kJ/mol
  • This energy represents approx. 688 Cal
  • or about two Snickers bars worth...
slide9
The Haber process for the production of ammonia involves the equilibrium
  • Assume that ΔH° and ΔS° for this reaction do not change with temperature.
  • Predict the direction in which ΔG° for this reaction changes with increasing temperature.
  • (b) Calculate the values ΔG° of for the reaction at 25 °C and 500 °C.

Sample Exercise 19.9 Determining the Effect of Temperature on Spontaneity

slide10
DG = DHsys - TDSsys
  • The temperature dependence of ΔG° comes from the entropy term.
  • We expect ΔS° for this reaction to be negative because the number of molecules of gas is smaller in the products.
  • Because ΔS° is negative, the term –T ΔS° is positive and grows larger with increasing temperature.
  • As a result, ΔG° becomes less negative (or more positive) with increasing temperature.
  • Thus, the driving force for the production of NH3 becomes smaller with increasing temperature.
slide11
The Haber process for the production of ammonia involves the equilibrium
  • Assume that ΔH° and ΔS° for this reaction do not change with temperature.
  • Predict the direction in which ΔG° for this reaction changes with increasing temperature.
  • (b) Calculate the values ΔG° of for the reaction at 25 °C and 500 °C.

Sample Exercise 19.9 Determining the Effect of Temperature on Spontaneity

slide12
DGo = DHsys - TDSsys
  • The reaction is spontaneous at 25 oC
  • The reaction is nonspontaneous at 500 oC
slide13
Gibbs Free Energy and Chemical Equilibrium
  • We need to distinguish between ΔG and ΔG°
  • During the course of a chemical reaction, not all
  • products and reactants will be in their standard states
      • In this case, we use ΔG
  • When the system reaches equilibrium, the sign of ΔG°
  • tells us whether products or reactants are favored
  • What is the relationship between ΔG and ΔG°?
slide14
Gibbs Free Energy and Chemical Equilibrium

When not all products and reactants are in their standard states:

ΔG = ΔG° + RT lnQ

R ≡ gas constant (8.314 J/K•mol)

T ≡ absolute temperature (K)

Q ≡ reaction quotient = [products]o / [reactants]o

At Equilibrium:

Q = K

ΔG = 0

0 = ΔG° + RT lnK

ΔG° = −RT lnK

slide15
DG° = -RT lnK

or

Table 19.5

slide16
Example

Calculate ΔG° for the following process at 25 °C:

BaF2(s)⇌ Ba2+(aq) + 2 F−(aq); Ksp = 1.7 x 10-6

ΔG = 0 for any equilibrium, so:

ΔG° = − RT ln Ksp

ΔG° = − (8.314 J/mol∙K) (298 K) ln (1.7 x 10-6)

ΔG° = + 32.9 kJ/mol

ΔG° ≈ + 33 kJ/mol

Equilibrium lies to the left

slide17
Thermodynamics in living systems
  • Many biochemical reactions have a positive ΔGo
  • In living systems, these reactions are coupled to a
  • process with a negative ΔGo (coupled reactions)
  • The favorable rxn drives the unfavorable rxn
slide18
C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O (l)

Metabolism of glucose in humans

ΔG° = -2880 kJ/mol

  • Does not occur in a single step as it would in simple
  • combustion
  • Enzymes break glucose down step-wise
  • Free energy released used to synthesize ATP from ADP:
slide19
Fig 19.20 Free Energy and Cell Metabolism

ΔG° = +31 kJ/mol

ADP + H3PO4→ ATP + H2O

(Free energy stored)

ad