AP Chem Gibbs free energy and spontaneity cheat sheet
This study set covers essential concepts of Gibbs free energy and spontaneity in AP Chemistry, including definitions, formulas, and applications.
Quiz(64 questions)
1. What does Gibbs Free Energy (G) measure in a thermodynamic system?
Terms in this Study Set(64)
Gibbs Free Energy Basics(16)
Gibbs Free Energy (G) → Definition
Gibbs Free Energy is a thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure.
Key Formula for Gibbs Free Energy
The formula is given by: , where H is enthalpy, T is temperature in Kelvin, and S is entropy.
True or False: G increases with spontaneity.
False. A spontaneous process has a negative change in Gibbs Free Energy (ΔG < 0).
ΔG = ΔH - TΔS → What do variables represent?
ΔG = change in Gibbs Free Energy, ΔH = change in enthalpy, T = temperature (K), ΔS = change in entropy.
Standard Gibbs Free Energy Change (ΔG°) → Definition
ΔG° is the change in Gibbs Free Energy under standard conditions (1 atm, 25°C, 1 M concentration).
Fill in the blank: At equilibrium, ΔG = _____
0. At equilibrium, the system is at its lowest energy state, and no net change occurs.
When is a reaction spontaneous?
A reaction is spontaneous if ΔG < 0, indicating that the process can occur without external energy.
Comparison: Entropy (S) vs. Gibbs Free Energy (G)
Entropy measures disorder in a system; Gibbs Free Energy indicates spontaneity and work potential.
What does a positive ΔG indicate?
A positive ΔG (> 0) indicates that the reaction is non-spontaneous under standard conditions.
Effect of temperature on ΔG?
Increasing temperature can affect ΔG depending on the signs of ΔH and ΔS, potentially making a non-spontaneous reaction spontaneous.
ΔG < 0 → Effect on equilibrium
If ΔG < 0, the reaction proceeds forward towards products, favoring product formation at equilibrium.
True or False: ΔG° can predict reaction direction.
True. ΔG° indicates whether a reaction is spontaneous at standard conditions.
Gibbs Free Energy relationship with Keq?
ΔG° = -RT ln(K_eq), where R is the gas constant (8.314 J/mol·K) and K_eq is the equilibrium constant.
What does a negative ΔH and positive ΔS imply?
A reaction with ΔH < 0 and ΔS > 0 is always spontaneous at all temperatures (ΔG < 0).
ΔG = 0 → What does this mean?
When ΔG = 0, the system is at equilibrium, and the rates of the forward and reverse reactions are equal.
Gibbs Free Energy Significance
Gibbs Free Energy helps predict the feasibility of reactions in biological, chemical, and physical processes.
Spontaneity and Conditions(16)
What are the signs of spontaneity?
ΔG < 0 (spontaneous), ΔG = 0 (equilibrium), ΔG > 0 (non-spontaneous).
Fill in the blank: A reaction is spontaneous at high temperature if ΔH is ____ and ΔS is ____.
ΔH is positive, ΔS is positive.
True or False: Increasing pressure favors reactions with fewer moles of gas.
True - It shifts equilibrium toward fewer gas molecules, increasing spontaneity.
Effect of temperature on spontaneity?
Temperature affects ΔG through ΔG = ΔH - TΔS. High T favors positive ΔS.
What is the relationship between ΔH and spontaneity?
Exothermic reactions (ΔH < 0) favor spontaneity, especially at low temperatures.
List factors affecting spontaneity.
- Temperature - Pressure - Enthalpy (ΔH) - Entropy (ΔS)
What does a positive ΔS indicate?
Increase in disorder or randomness, often favors spontaneity.
Cause → Effect: High ΔH and low ΔS?
Low spontaneity; reactions are less likely to occur.
Calculate ΔG given ΔH = 100 kJ and ΔS = 0.1 kJ/K at 300 K.
ΔG = ΔH - TΔS = 100 kJ - (300 K)(0.1 kJ/K) = 70 kJ.
What role does entropy (ΔS) play?
ΔS increases disorder; higher ΔS typically increases spontaneity.
True or False: All endothermic reactions are non-spontaneous.
False - If ΔS is positive and large enough, ΔG can be negative.
What happens to spontaneity at low temperatures?
Reactions with negative ΔH are more likely to be spontaneous.
Comparison: Standard conditions vs. non-standard conditions.
Standard: 1 atm, 25°C; Non-standard: varying pressure and temperature conditions.
Fill in the blank: At equilibrium, ΔG is ____.
ΔG is zero.
What is the effect of increasing temperature on ΔG for an endothermic process?
ΔG decreases, increasing the likelihood of spontaneity.
How does pressure influence gas reactions?
Increasing pressure favors the formation of products with fewer gas moles.
Calculating Gibbs Free Energy(16)
Gibbs Free Energy Formula?
where G = Gibbs free energy, H = enthalpy, T = temperature (K), S = entropy.
Conditions for Gibbs Free Energy change
ΔG = ΔH - TΔS. Use when determining spontaneity.
True or False: ΔG < 0 indicates non-spontaneous reaction.
False. ΔG < 0 indicates spontaneous reaction.
Calculate ΔG given: ΔH = -200 kJ, ΔS = 0.5 kJ/K, T = 298 K.
ΔG = ΔH - TΔS = -200 - (298)(0.5) = -200 - 149 = -349 kJ.
Significance of ΔG = 0?
Reaction is at equilibrium; no net change occurs.
Fill in the blank: When ΔG > 0, the reaction is __________.
non-spontaneous.
Relationship between ΔG and spontaneity
ΔG < 0: spontaneous; ΔG = 0: equilibrium; ΔG > 0: non-spontaneous.
What influences ΔG?
Temperature, pressure, enthalpy, entropy.
Calculate ΔG from standard conditions formula
Use: ΔG° = ΔH° - TΔS° at standard conditions.
Determine ΔG at 100°C: ΔH = -250 kJ, ΔS = 0.75 kJ/K.
Convert T to K: 100°C = 373 K. ΔG = -250 - 373(0.75) = -250 - 279.75 = -529.75 kJ.
How to relate ΔG and K?
Use: ΔG° = -RT ln(K) where R = 8.314 J/(mol·K), T in K.
True or False: Higher entropy leads to more stable systems.
True. Higher entropy corresponds to greater disorder, often more stability.
Effect of temperature on spontaneity of reactions?
ΔG depends on T: Higher T can make ΔG negative if ΔS is positive.
Compare ΔG° and ΔG.
ΔG°: standard conditions; ΔG: actual conditions.
How to find ΔS if ΔG and ΔH are known?
Rearrange: ΔS = (ΔH - ΔG) / T.
Calculate ΔG from ΔG° and Q.
ΔG = ΔG° + RT ln(Q). Use for non-standard conditions.
Applications and Examples(16)
Gibbs Free Energy in Car Engine?
Car engines convert chemical energy of fuel (Gibbs Free Energy decrease) into mechanical work.
True or False: Non-spontaneous processes can occur.
True - They require continuous energy input to proceed.
Fill in the blank: If ΔG < 0, the process is _____.
spontaneous.
Gibbs Free Energy at Equilibrium?
ΔG = 0 at equilibrium; no net change in reactants or products.
Effect of Temperature on Spontaneity?
Increasing temperature can make non-spontaneous reactions spontaneous if ΔH is positive and ΔS is high.
Calculate ΔG for freezing water.
At 0°C, ΔG = ΔH - TΔS. With ΔH = -6.01 kJ/mol and ΔS = -22 J/(mol·K): ΔG = -6.01 - (273)(-0.022) = 0.
Gibbs Free Energy in Photosynthesis?
Photosynthesis has a ΔG > 0; it is non-spontaneous and requires sunlight energy.
Comparison: ΔG and spontaneity.
ΔG < 0 → spontaneous; ΔG = 0 → equilibrium; ΔG > 0 → non-spontaneous.
Example of spontaneous process.
Rusting of iron: it's spontaneous due to favorable entropy and energy changes.
What influences ΔG?
Temperature, pressure, concentration of reactants and products.
What is ΔG for a reaction at standard conditions?
ΔG° can predict spontaneity at 25°C, 1 atm, 1 M concentrations.
Cause of non-spontaneity in combustion?
Higher activation energy barriers or enthalpy of reactants exceeding products.
True or False: Higher temperature decreases ΔG.
False - Higher temperature can increase ΔG in endothermic reactions.
Example of ΔG in biological systems.
ATP hydrolysis releases energy (ΔG < 0) used for cellular work.
Free energy in industry?
Gibbs Free Energy calculations help optimize reactions in pharmaceuticals, plastics, and energy sectors.
Spontaneity of melting ice in summer?
Melting ice (ΔG < 0) is spontaneous in warmer temperatures due to higher entropy.
Questions in this Study Set(64)
1. What does Gibbs Free Energy (G) measure in a thermodynamic system?
2. What is the Gibbs free energy change (ΔG) for a spontaneous reaction?
3. What is the correct formula for calculating Gibbs Free Energy?
4. What does a negative ΔG indicate about a chemical reaction?
5. If a reaction has a ΔG > 0, what does this indicate about its spontaneity?
6. For a reaction to be spontaneous at low temperatures, the enthalpy change (ΔH) is typically...
7. Under what condition is a reaction considered spontaneous based on Gibbs Free Energy?
8. In which scenario is the reaction considered non-spontaneous?
9. Which formula correctly expresses the relationship between Gibbs Free Energy, enthalpy, and entropy?
10. Which of the following changes will increase the spontaneity of a reaction?
11. If ΔG = 0 for a reaction, what does this indicate?
12. Which expression correctly relates ΔG to ΔH and ΔS?
13. Fill in the blank: At equilibrium, ΔG = _____
14. At equilibrium, what is true about the Gibbs free energy change (ΔG)?
15. Calculate ΔG when ΔH = -150 kJ, ΔS = 0.6 kJ/K, and T = 298 K.
16. At what conditions is ΔG equal to zero?
17. What does a positive change in entropy (ΔS) generally suggest about a reaction?
18. What does a positive change in entropy (ΔS) signify in a reaction?
19. What happens to ΔG if temperature increases while ΔS is positive?
20. Which factor does NOT influence the value of ΔG?
21. Which of the following indicates that a reaction is spontaneous?
22. If ΔH is positive and ΔS is also positive, at what condition is the reaction spontaneous?
23. Which of the following correctly describes ΔG°?
24. What happens to the spontaneity of a reaction when temperature increases if ΔH is positive and ΔS is high?
25. How does increasing temperature affect ΔG when ΔH is negative and ΔS is positive?
26. Which statement correctly describes the effect of increasing temperature on ΔG for an exothermic reaction?
27. Fill in the blank: When ΔG > 0, the reaction is __________.
28. What is the standard condition for measuring ΔG°?
29. True or False: A reaction with ΔH > 0 and ΔS < 0 can never be spontaneous.
30. What is the result of a reaction with high ΔH and high ΔS at low temperatures?
31. What is the relationship between ΔG and the equilibrium constant K?
32. Which process is an example of a spontaneous process?
33. What does a negative ΔH and a negative ΔS imply about a reaction's spontaneity?
34. Which of the following correctly describes a system at standard conditions?
35. True or False: Higher entropy always leads to greater stability in systems.
36. What is the effect of increasing temperature on ΔG of an endothermic reaction?
37. What is the standard Gibbs Free Energy change (ΔG°)?
38. If the entropy change (ΔS) is zero, what can be said about the spontaneity of the reaction?
39. How can you find ΔS if ΔG and ΔH are known?
40. What role does Gibbs free energy play in biological systems?
41. Which of the following is NOT a characteristic of Gibbs Free Energy?
42. Which of the following statements is NOT true about spontaneity?
43. Calculate ΔG from standard conditions when ΔG° = -100 kJ and Q = 10.
44. Which of the following statements is true regarding non-spontaneous processes?
45. What happens to a reaction if ΔG < 0 as it approaches equilibrium?
46. In an endothermic reaction, what happens to ΔG as temperature increases?
47. Which of the following factors does NOT influence ΔG?
48. How does ΔG relate to the reaction's enthalpy and entropy?
49. According to the equation ΔG° = -RT ln(K_eq), what does K_eq represent?
50. How does high entropy (ΔS) influence reactions involving gas molecules?
51. What does a negative ΔH and a positive ΔS indicate about a reaction?
52. Which process would have a positive ΔG at standard conditions?
53. What does a ΔG of 0 signify about a chemical system?
54. What is a common characteristic of reactions that are non-spontaneous?
55. Which equation is used to calculate ΔG from non-standard conditions?
56. What is the primary cause of non-spontaneity in some combustion reactions?
57. Which statement best describes the significance of Gibbs Free Energy?
58. Which of the following conditions will ensure that a reaction is spontaneous at high temperatures?
59. What does it imply if ΔG is equal to the standard enthalpy change ΔH?
60. Which of the following would NOT be a consideration in Gibbs Free Energy calculations for industrial applications?
61. Which of the following statements about Gibbs Free Energy is FALSE?
62. For a reaction that has a large positive ΔS, which of the following statements is true regarding its spontaneity?
63. Calculate ΔG for a reaction at 298 K if ΔH = -150 kJ and ΔS = 0.4 kJ/K.
64. Which of the following is an example of a process that is spontaneous at room temperature?
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