Spontaneity of reactions examples

📚 Quick Study Guide

• 🔥 Spontaneity: Refers to the inherent tendency of a reaction to occur without continuous external influence.
• 🌡️ Temperature Dependence: Spontaneity can be heavily influenced by temperature. Some reactions are only spontaneous above or below a certain temperature.
• 🔄 Reversible Reactions: Many reactions are reversible, meaning they can proceed in both forward and reverse directions. Spontaneity considerations apply to both directions.
• 📏 Gibbs Free Energy: A thermodynamic potential that measures the amount of energy available in a chemical or physical system to do useful work at a constant temperature and pressure.
• 📝 Gibbs Free Energy Equation: The change in Gibbs Free Energy ($\Delta G$) determines spontaneity:
  • $\Delta G < 0$: Spontaneous reaction
  • $\Delta G > 0$: Non-spontaneous reaction
  • $\Delta G = 0$: Reaction at equilibrium
• 🧮 Calculating Gibbs Free Energy: $\Delta G = \Delta H - T\Delta S$, where:
  • $\Delta H$ is the change in enthalpy (heat)
  • $T$ is the absolute temperature (in Kelvin)
  • $\Delta S$ is the change in entropy (disorder)
• 🔑 Enthalpy & Entropy: A reaction is more likely to be spontaneous if it is exothermic ($\Delta H < 0$) and increases entropy ($\Delta S > 0$).

🧪 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. Which factor does NOT directly affect the spontaneity of a reaction?
   1. Enthalpy change
   2. Entropy change
   3. Temperature
   4. Activation energy
3. For a reaction where both $\Delta H$ and $\Delta S$ are positive, spontaneity is favored by:
   1. Low temperatures
   2. High temperatures
   3. All temperatures
   4. None of the above
4. What is the standard unit of Gibbs Free Energy?
   1. Joules (J)
   2. Kelvin (K)
   3. Moles (mol)
   4. Pascal (Pa)
5. A reaction has $\Delta H = -100 \text{ kJ}$ and $\Delta S = +50 \text{ J/K}$. At what temperature is the reaction at equilibrium ($\Delta G = 0$)?
   1. 2 K
   2. 200 K
   3. 2000 K
   4. -2000 K
6. Which of the following reactions is most likely to be spontaneous at all temperatures?
   1. $\Delta H > 0$, $\Delta S < 0$
   2. $\Delta H < 0$, $\Delta S < 0$
   3. $\Delta H > 0$, $\Delta S > 0$
   4. $\Delta H < 0$, $\Delta S > 0$
7. Which statement is true about non-spontaneous reactions?
   1. They always require a catalyst.
   2. They cannot occur under any circumstances.
   3. They require continuous external energy input to proceed.
   4. They proceed quickly.