Real-World Examples of Gibbs Free Energy in Chemical Reactions

📚 Quick Study Guide

• 🌡️ Gibbs Free Energy ($G$) predicts the spontaneity of a reaction.
• 📝 The formula is: $G = H - TS$, where $H$ is enthalpy, $T$ is temperature (in Kelvin), and $S$ is entropy.
• 📉 A negative $G$ indicates a spontaneous reaction.
• 📈 A positive $G$ indicates a non-spontaneous reaction.
• ⚖️ $G = 0$ indicates the reaction is at equilibrium.

🧪 Practice Quiz

1. Which of the following reactions is most likely to be spontaneous at room temperature?
   1. A. A reaction with $\Delta H = +100 kJ$ and $\Delta S = +10 J/K$
   2. B. A reaction with $\Delta H = -50 kJ$ and $\Delta S = +100 J/K$
   3. C. A reaction with $\Delta H = +50 kJ$ and $\Delta S = -100 J/K$
   4. D. A reaction with $\Delta H = -100 kJ$ and $\Delta S = -10 J/K$
2. Rusting of iron is a common example of a spontaneous process. What can be inferred about the Gibbs Free Energy change ($\Delta G$) for this process?
   1. A. $\Delta G > 0$
   2. B. $\Delta G < 0$
   3. C. $\Delta G = 0$
   4. D. Cannot be determined with the information given.
3. Consider the reaction: $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$. Under what conditions would this reaction be most favored (spontaneous)? Given that the reaction is exothermic.
   1. A. High temperature, high pressure
   2. B. Low temperature, high pressure
   3. C. High temperature, low pressure
   4. D. Low temperature, low pressure
4. Melting of ice at room temperature (above 0°C) is a spontaneous process. What must be true about the change in Gibbs Free Energy for this process?
   1. A. $\Delta G$ is positive
   2. B. $\Delta G$ is negative
   3. C. $\Delta G$ is zero
   4. D. $\Delta G$ is temperature dependent but always positive
5. For a reaction to be non-spontaneous at all temperatures, what must be true regarding enthalpy ($\Delta H$) and entropy ($\Delta S$)?
   1. A. $\Delta H$ is negative and $\Delta S$ is positive
   2. B. $\Delta H$ is positive and $\Delta S$ is negative
   3. C. $\Delta H$ and $\Delta S$ are both positive
   4. D. $\Delta H$ and $\Delta S$ are both negative
6. Which of the following best describes a reaction at equilibrium in terms of Gibbs Free Energy?
   1. A. The system is moving towards maximum disorder.
   2. B. The forward and reverse reaction rates are equal, and $\Delta G = 0$.
   3. C. The reaction proceeds to completion.
   4. D. The system is at its lowest possible energy state.
7. A scientist is studying a new reaction and calculates $\Delta H = -50 kJ/mol$ and $\Delta S = -100 J/(mol \cdot K)$. Below what temperature (in Kelvin) will this reaction be spontaneous?
   1. A. 500 K
   2. B. 250 K
   3. C. 1000 K
   4. D. The reaction is spontaneous at all temperatures