If a reaction is exothermic and there is a great disorder, it means that?

Analysis of the Question

This question tests your understanding of the Gibbs Free Energy equation, which determines the spontaneity of a chemical reaction. You are asked to determine what happens to the free energy when a reaction is exothermic and leads to a great increase in disorder.

Concept Explanation

To solve this, we use the Gibbs Free Energy equation:

Where:

• $\Delta G$ is the change in Gibbs Free Energy.
• $\Delta H$ is the change in Enthalpy (heat content).
• $T$ is the absolute temperature (in Kelvin).
• $\Delta S$ is the change in Entropy (disorder).

Key Principles:

1. Exothermic reaction: The system releases heat, so $\Delta H$ is negative ($-$).
2. Great disorder: The system becomes more disordered, so $\Delta S$ is positive ($+$).
3. Spontaneity: For a reaction to be spontaneous, $\Delta G$ must be negative. A large decrease in free energy indicates a highly spontaneous reaction.

Step-by-Step Solution

1. Substitute the signs into the equation: • $\Delta H$ is negative ($-$). • $\Delta S$ is positive ($+$).
2. The equation becomes: $$\Delta G = (\text{negative}) - T(\text{positive})$$
3. Since $T$ is always positive, $-T(\text{positive})$ results in a negative value.
4. Therefore, $\Delta G = (\text{negative}) - (\text{positive}) = \text{a larger negative value}$.
5. A large negative value for $\Delta G$ represents a large decrease in free energy. This confirms that the reaction is highly spontaneous.

Conclusion

When a reaction is exothermic ($\Delta H < 0$) and results in increased disorder ($\Delta S > 0$), the Gibbs Free Energy ($\Delta G$) becomes significantly negative. This is described as a large decrease in free energy.

Exam Tip

Remember the "Spontaneity Table":

• If $\Delta H$ is negative and $\Delta S$ is positive, the reaction is spontaneous at all temperatures.
• Think of "Free Energy" like a bank account: if a reaction is "spontaneous," it is "spending" its energy to happen, hence a "decrease" in free energy!