In which of the following conditions, a reaction will definitely be spontaneous:

Options

A. Exothermic and increasing disorder
B. Exothermic and decreasing disorder
C. Endothermic and increasing disorder
D. Endothermic and decreasing disorder

Answer

To determine the conditions under which a reaction will definitely be spontaneous, we can analyze the relationship between Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS).

### Step-by-Step Solution:

1. **Understanding Spontaneity**: A reaction is considered spontaneous if it occurs without needing to be driven by an external force. The spontaneity of a reaction can be predicted using Gibbs free energy.

2. **Gibbs Free Energy Equation**: The Gibbs free energy change (ΔG) is given by the equation:
\[ \Delta G = \Delta H - T \Delta S \]
where:
- ΔG = change in Gibbs free energy
- ΔH = change in enthalpy
- T = temperature in Kelvin
- ΔS = change in entropy

3. **Condition for Spontaneity**: For a reaction to be spontaneous, ΔG must be less than 0 (ΔG < 0). This means that the reaction will occur naturally without external input.

4. **Analyzing ΔG**:
- If ΔH is negative (ΔH < 0), the reaction is exothermic, meaning it releases heat.
- If ΔS is positive (ΔS > 0), the disorder of the system increases.

5. **Combining Conditions**:
- If both ΔH is negative and ΔS is positive, then:
\[ \Delta G = \Delta H - T \Delta S < 0 \]
- This indicates that the reaction will definitely be spontaneous under these conditions.

6. **Conclusion**: Therefore, a reaction will definitely be spontaneous if it is exothermic (ΔH < 0) and results in an increase in disorder (ΔS > 0).

### Final Answer:
A reaction will definitely be spontaneous if it is exothermic (ΔH < 0) and leads to an increase in entropy (ΔS > 0).

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