Which of the following values of heat of formation indicates that the product is least stable?

Options

A. `-94" Kcal"`
B. `-231.5" Kcal"`
C. `+21.4 " Kcal"`
D. `+64.8" Kcal"`

Answer

To determine which value of heat of formation indicates that the product is least stable, we need to analyze the concept of heat of formation (ΔH_f). The heat of formation refers to the change in enthalpy when one mole of a compound is formed from its constituent elements in their standard states.

### Step-by-Step Solution:

1. **Understanding Heat of Formation**:
- The heat of formation (ΔH_f) can be either negative or positive. A negative ΔH_f indicates that the reaction is exothermic, meaning energy is released during the formation of the product. Conversely, a positive ΔH_f indicates that the reaction is endothermic, meaning energy must be absorbed for the product to form.

2. **Stability of Products**:
- Generally, products formed in exothermic reactions (negative ΔH_f) are more stable because they release energy. In contrast, products formed in endothermic reactions (positive ΔH_f) are less stable since they require energy input for their formation.

3. **Comparing Positive Values**:
- Among the given options, we compare the positive values of heat of formation. The larger the positive value, the more energy is required for the formation of the product, indicating lower stability.
- For example, if we have two positive ΔH_f values: +21.4 kcal and +64.8 kcal, we can conclude that the product with +64.8 kcal is less stable because it requires more energy for its formation compared to the product with +21.4 kcal.

4. **Conclusion**:
- Therefore, the product with the highest positive heat of formation value indicates the least stability. In this case, the option with +64.8 kcal is the correct answer, meaning that this product is the least stable.

### Final Answer:
The product with a heat of formation of +64.8 kcal is the least stable.

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