Chemistry 2010 JAMB Past Questions - Question 27: If a reaction is exothermic and there is a great disorder, it means that

Correct Answer

C

Explanation

The statement "If a reaction is exothermic and there is a great disorder" doesn't necessarily lead to **a large decrease in free energy**. While the information helps with understanding some aspects of the reaction, it's not enough to definitively determine the free energy change (ΔG). Here's why:

**Exothermic reactions:**

- These reactions release energy to the surroundings (ΔH < 0) and are often considered spontaneous. However, spontaneity is not solely determined by enthalpy (heat).

**Disorder (entropy):**

- Increased disorder (ΔS > 0) generally favors spontaneity. However, the magnitude of the entropy change depends on the specific reaction and the state of reactants and products.

**Free energy (ΔG):**

- The combined effect of enthalpy and entropy determines the spontaneity of a reaction through the equation: ΔG = ΔH - TΔS, where T is the absolute temperature.
- Even if a reaction is exothermic and has increased disorder, a large positive ΔS might not be enough to overcome a very negative ΔH, resulting in a positive ΔG and a non-spontaneous reaction.

Therefore, to accurately assess the free energy change and spontaneity of a reaction, you need to consider **both** the enthalpy and entropy changes based on the specific reaction context, including:

- The magnitude of ΔH and ΔS.
- The temperature at which the reaction occurs (T affects the ΔS term).
- The specific reactants and products involved.

With this information, you can calculate the ΔG and determine whether the reaction is spontaneous (ΔG < 0) or non-spontaneous (ΔG > 0).