1 1 Contents and Concepts 1. First Law of Thermodynamics 2. Entropy and the Second Law of Thermodynamics 3. Standard Entropies and the Third Law of Thermodynamics Spontaneous Processes and Entropy A spontaneous process is one that occurs by itself. As we will see, the entropy of the system increases in a spontaneous process. 2 Free-Energy Concept The quantity ΔH – TΔS can function as a criterion for the spontaneity of a reaction at constant temperature, T, and pressure, P. By defining a quantity called the free energy, G = H – TS, we find that ΔG equals the quantity ΔH – TΔS, so the free energy gives us a thermodynamic criterion of spontaneity. 4. Free Energy and Spontaneity 5. Interpretation of Free Energy 3 Free Energy and Equilibrium Constants The total free energy of the substances in a reaction mixture decreases as the reaction proceeds. As we discuss, the standard free-energy change for a reaction is related to its equilibrium constant. 6. Relating ΔG° to the Equilibrium Constant 7. Change of Free Energy with Temperature 4 • First Law of Thermodynamics; Enthalpy a. Define internal energy, state function, work, and first law of thermodynamics. b. Explain why the work done by the system as a result of expansion or contraction during a chemical reaction is -PΔV. Learning Objectives 5 1. First Law of Thermodynamics; Enthalpy (cont) • c. Relate the change of internal energy, ΔU, and heat of reaction, q. • d. Define enthalpy, H. • e. Show how heat of reaction at constant pressure, q p , equals the change of enthalpy, ΔH. 6 Spontaneous Processes and Entropy 2. Entropy and the Second Law of Thermodynamics • a. Define spontaneous process. • b. Define entropy. • c. Relate entropy to disorder in a molecular system (energy dispersal). • d. State the second law of thermodynamics in terms of system plus surroundings.
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Contents and Concepts
1. First Law of Thermodynamics
2. Entropy and the Second Law of Thermodynamics
3. Standard Entropies and the Third Law of Thermodynamics
Spontaneous Processes and Entropy
A spontaneous process is one that occurs by itself. As we will see, the entropy of the system
increases in a spontaneous process.
2
Free-Energy Concept
The quantity ∆H – T∆S can function as a criterion
for the spontaneity of a reaction at constant temperature, T, and pressure, P. By defining a quantity called the free energy, G = H – TS, we
find that ∆G equals the quantity ∆H – T∆S, so the free energy gives us a thermodynamic criterion of spontaneity.
4. Free Energy and Spontaneity
5. Interpretation of Free Energy
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Free Energy and Equilibrium Constants
The total free energy of the substances in a reaction mixture decreases as the reaction
proceeds. As we discuss, the standard free-energy change for a reaction is related to its equilibrium constant.
6. Relating ∆G° to the Equilibrium Constant
7. Change of Free Energy with Temperature
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• First Law of Thermodynamics;
Enthalpy
a. Define internal energy, state function, work, and first law of thermodynamics.
b. Explain why the work done by the system
as a result of expansion or contraction during a chemical reaction is -P∆V.
Learning Objectives
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1. First Law of Thermodynamics;
Enthalpy (cont)
• c. Relate the change of internal energy, ∆U, and heat of reaction, q.
• d. Define enthalpy, H.
• e. Show how heat of reaction at constant pressure, qp, equals the change of
enthalpy, ∆H.
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Spontaneous Processes and Entropy
2. Entropy and the Second Law of
Thermodynamics
• a. Define spontaneous process.
• b. Define entropy.
• c. Relate entropy to disorder in a molecular system (energy dispersal).
• d. State the second law of thermodynamics in terms of system plus
surroundings.
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2. Entropy and the Second Law of
Thermodynamics (cont)
– e. State the second law of thermodynamics in terms of the system only.
• f. Calculate the entropy change for a phase transition.
• g. Describe how ∆H - T∆S functions as a criterion of a spontaneous reaction.
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3. Standard Entropies and the Third Law
of Thermodynamics
– a. State the third law of thermodynamics.
– b. Define standard entropy (absolute entropy).
– c. State the situations in which the entropy usually increases.
– d. Predict the sign of the entropy change of a reaction.
– e. Express the standard change of entropy of a reaction in terms of standard
entropies of products and reactants.
– f. Calculate ∆So for a reaction.
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Free-Energy Concept
4. Free Energy and Spontaneity
– a. Define free energy, G.
– b. Define the standard free-energy change.
– c. Calculate ∆Go from ∆Ho and ∆So.
– d. Define the standard free energy of
formation, ∆Go.
– e. Calculate ∆Go from standard free energies of formation.
– f. State the rules for using ∆Go as a
criterion for spontaneity
– g. Interpret the sign of ∆Go.
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5. Interpretation of Free Energy
– a. Relate the free-energy change to maximum useful work.
– b. Describe how the free energy changes during a chemical reaction.
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Free Energy and Equilibrium Constants
6. Relating ∆Go to the Equilibrium Constant
– a. Define the thermodynamic equilibrium constant, K.
– b. Write the expression for a thermodynamic equilibrium constant.
– c. Indicate how the free-energy change of a reaction and the reaction quotient are related.
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6. Relating ∆Go to the Equilibrium
Constant (cont)
– d. Relate the standard free-energy change to the thermodynamic equilibrium constant.
– e. Calculate K from the standard free-energy change (molecular equation).
– f. Calculate K from the standard free-energy change (net ionic equation).
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7. Change of Free Energy with
Temperature
– a. Describe how ∆Go at a given temperature (∆Go
T) is approximately related to ∆Ho and ∆So at that temperature.
– b. Describe how the spontaneity or nonspontaneity of a reaction is related to each of the four possible combinations of
signs of ∆Ho and ∆So.
– c. Calculate ∆Go and K at various temperatures.
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Chapter 13 Chemical Thermodynamics
1. Spontaneous Chemical and Physical Processes
2. Entropy and Disorder
3. Entropy and the Second Law of Thermodynamics
4. Standard-State Entropies of Reaction
5. The Third Law of Thermodynamics
6. Calculating Entropy Changes for Chemical Reactions
7. Gibbs Free Energy
8. The Effect of Temperature on the Free Energy of a Reaction
9. Beware of Oversimplification
10. Stand-State Free Energies of Reaction
11. Equilibria Expressed in Partial Pressures
12. Interpreting Stand-State Free Energy of Reaction Data
13. Relationship Between Free Energy and Equilibrium Constants
14. Temperature Dependence of Equilibrium Constants
15. Gibbs Free Energies of Formation and Absolute Entropies
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Thermodynamics and Equilibrium
Thermodynamics: Define
The study of the relationship between
heat and other forms of energy
involved in a chemical or physical
process
How do we use this knowledge in chemistry?
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2 NH3 (g) + CO2 (g) → NH2CONH2 (aq) + H2O (l)
Consider this Reaction
Concerning this reaction:
1. Does this reaction naturally occur as written?
2. Will the reaction mixture contain sufficient
amount of product at equilibrium?
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We can answer these questions with
heat measurements only!!!
1. We can predict the natural direction.
2. We can determine the composition of the
mixture at equilibrium.
How?
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Consider the Laws of Thermodynamics
1st Law: The change in internal energy of a
system ∆U, equals q + w
∆U = q + w
2nd Law: The total entropy of a system and its
surroundings increases for a spontaneous
process.
3rd Law: A substance that is perfectly crystalline
at 0 K has an entropy of zero.
You can’t win
You cant break even.
You can’t quit the game
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1st Law: The change in internal energy of a
system ∆U, equals q + w
∆U = q + w
∆U = Internal energy = Sum of kinetic energy and
potential energy of the
particle making up the system.
Kinetic Energy = Energy of motion of electrons, protons
and molecules.
Potential Energy = Energy from chemical bonding of