Questions and Answers
What does the Third Law of Thermodynamics state about the entropy of a perfectly crystalline substance at 0 K?
In standard state conditions, what is typically the temperature used when determining standard absolute entropies?
Which state of matter has the highest relative standard entropy at a given temperature?
How does molar mass affect the entropy of a substance?
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What can be concluded about the relative standard entropies of different allotropes?
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What is true about the entropy of dissolved solids compared to their undissolved counterparts?
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What is the effect of molecular complexity on standard entropy?
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Which characteristic of a system can indicate that a process will be spontaneous?
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Under what conditions will Gibbs Free Energy, G, be negative?
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When is a reaction considered to be spontaneous in terms of G° and K?
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What does it mean when G = 0 in terms of the reaction?
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Which statement accurately describes the relationship between G° and the reaction quotient Q?
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Which conditions imply that G° is positive?
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What contributes to the standard free energy change G°?
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How does the thermodynamic equilibrium constant K behave with temperature changes?
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What must be true about all reactants and products for G = G°?
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What happens to the standard free energy change (G°) of a reaction when it is spontaneous?
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Which statement accurately describes the free energy (G) in thermodynamics?
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What is the value of the standard free energy of formation (Gf°) for elements in their most stable states?
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During a reaction, if free energy decreases, what other thermodynamic quantity is likely increasing?
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What defines a reaction where G° has a small negative value?
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Why is the energy termed 'free' in free energy?
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In which situation is a reaction considered nonspontaneous based on standard free energy change?
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What occurs when a system has more energy states available during a reaction?
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Study Notes
Free Energy (G)
- Free energy (G) is calculated using the formula G = H – TS, linking enthalpy (H), temperature (T), and entropy (S).
- A negative G indicates a spontaneous reaction, while a positive S contributes to a negative G.
Standard Free Energy of Formation, Gf°
- Gf° measures free-energy change when 1 mole of substance forms from its elements at standard conditions (1 atm, specified temperature).
- Elements in their most stable state have a Gf° value of zero.
Spontaneity of a Reaction using G°
- A large negative G° signifies that the reaction is spontaneous, with near-complete transformation from reactants to products.
- A large positive G° indicates nonspontaneity, meaning reactants yield minimal products.
- Small positive or negative G° suggests an equilibrium scenario with significant amounts of both reactants and products.
Concept of "Free" Energy
- Free energy is the maximum energy available to perform work from a system.
- In exothermic reactions, some released heat increases surrounding entropy, reducing work availability.
Free Energy Change During a Reaction
- A decrease in free energy can result in work done and an increase in entropy.
Gibbs Free Energy, G
- G is negative for spontaneous processes under conditions:
- Negative H and positive S (exothermic, increased disorder).
- Negative large H and small negative S.
- Positive small H and large positive S, or high temperature.
- G is positive when H is positive and S negative (never spontaneous).
Relating G° to the Equilibrium Constant, K
- G equals G° only at standard states (1 atm for gases, 1 M for solutes).
- Under nonstandard conditions, the equation is G = G° + RT ln Q; at equilibrium, G = 0, which relates G° and K: G° = -RT ln K.
Thermodynamic Equilibrium Constant, K
- K is derived from concentrations expressed as partial pressures (gases) or molarities (solutions) at standard conditions.
Spontaneity using G° and K
- At equilibrium (G = 0), if K > 1, G° is negative, indicating spontaneity; K < 1 means G° is positive, indicating nonspontaneity.
Third Law of Thermodynamics
- A perfectly crystalline substance at 0 K has zero entropy; all other substances possess positive entropy.
Standard Absolute Entropies, S°
- S° represents standard state conditions, defining entropy for 1 mole of a substance typically at 298 K.
Relative Standard Entropies: States
- Gases have greater entropy than liquids, and liquids have greater entropy than solids at a corresponding temperature.
Relative Standard Entropies: Molar Mass
- Higher molar mass correlates with larger entropy due to closely spaced energy states.
Relative Standard Entropies: Allotropes
- Less constrained structures (e.g., graphite) exhibit higher entropy.
Relative Standard Entropies: Dissolution
- Dissolved solids usually possess higher entropy due to particle distribution throughout mixtures.
Relative Standard Entropies: Molecular Complexity
- Larger, more complex molecules generally have increased entropy compared to simpler structures.
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Description
Explore the concepts of free energy and its relation to thermodynamics. This quiz covers essential principles such as the equation G = H - TS and the spontaneity of reactions. Test your understanding of standard free energy changes and their implications in chemical processes.
