AP Chemistry Questions: Mastering Gibbs Free Energy Concepts

📚 Quick Study Guide

• 🌡️ Gibbs Free Energy ($G$) predicts the spontaneity of a reaction at constant temperature and pressure.
• 📝 The change in Gibbs Free Energy ($\Delta G$) is related to enthalpy ($\Delta H$), entropy ($\Delta S$), and temperature ($T$) by the equation: $\Delta G = \Delta H - T\Delta S$.
• ⚛️ A reaction is spontaneous (thermodynamically favorable) when $\Delta G < 0$.
• ⚖️ A reaction is at equilibrium when $\Delta G = 0$.
• 📈 A reaction is non-spontaneous when $\Delta G > 0$.
• 🔢 Standard Gibbs Free Energy change ($\Delta G^\circ$) refers to the change when reactants and products are in their standard states (usually 1 atm or 1 M).
• ⚗️ $\Delta G = \Delta G^\circ + RT\ln Q$, where $R$ is the gas constant (8.314 J/mol·K) and $Q$ is the reaction quotient.
• 💡 Gibbs Free Energy is state function.

🧪 Practice Quiz

1. Which of the following conditions indicates a spontaneous reaction at constant temperature and pressure?
   1. $\Delta G > 0$
   2. $\Delta G < 0$
   3. $\Delta G = 0$
   4. $\Delta H = 0$
2. For a reaction to be spontaneous at all temperatures, which of the following conditions must be true?
   1. $\Delta H > 0$, $\Delta S > 0$
   2. $\Delta H < 0$, $\Delta S < 0$
   3. $\Delta H < 0$, $\Delta S > 0$
   4. $\Delta H > 0$, $\Delta S < 0$
3. What is the value of $\Delta G$ at equilibrium?
   1. $\Delta G > 0$
   2. $\Delta G < 0$
   3. $\Delta G = 0$
   4. $\Delta G = 1$
4. The change in Gibbs Free Energy ($\Delta G$) is given by which equation?
   1. $\Delta G = \Delta H + T\Delta S$
   2. $\Delta G = \Delta H - T\Delta S$
   3. $\Delta G = T\Delta H - \Delta S$
   4. $\Delta G = -\Delta H - T\Delta S$
5. Which of the following affects the Gibbs Free Energy of a reaction?
   1. Temperature
   2. Pressure
   3. Concentration
   4. All of the above
6. Given $\Delta H = -100 \text{ kJ}$ and $\Delta S = -50 \text{ J/K}$ for a reaction, at what temperature will the reaction be spontaneous?
   1. $T < 2000 \text{ K}$
   2. $T > 2000 \text{ K}$
   3. $T < 2 \text{ K}$
   4. $T > 2 \text{ K}$
7. The standard Gibbs free energy change ($\Delta G^\circ$) is related to the equilibrium constant ($K$) by which equation?
   1. $\Delta G^\circ = -RT\ln K$
   2. $\Delta G^\circ = RT\ln K$
   3. $\Delta G^\circ = -\frac{R}{T}\ln K$
   4. $\Delta G^\circ = \frac{R}{T}\ln K$