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

Options

A. `-100 k Cal`
B. `-200kCal`
C. `+20kCal`
D. `+60 kCal`

Answer

To determine which value of heat of formation indicates that a product is least stable, we need to understand the concept of heat of formation (ΔHf). Here’s a step-by-step solution:

### Step 1: Understand Heat of Formation
Heat of formation (ΔHf) is the change in enthalpy when one mole of a compound is formed from its constituent elements in their standard states.

### Step 2: Analyze the Sign of ΔHf
- If ΔHf is negative, it indicates that energy is released when the compound is formed. This generally suggests that the compound is stable because it has lower energy.
- If ΔHf is positive, it indicates that energy is absorbed when the compound is formed. This suggests that the compound is less stable because it has higher energy.

### Step 3: Compare Magnitudes of ΔHf
- Among the negative values, a more negative ΔHf indicates greater stability. For example, -100 kJ/mol is more stable than -50 kJ/mol.
- Among the positive values, a higher positive ΔHf indicates greater instability. For example, +60 kJ/mol is less stable than +30 kJ/mol.

### Step 4: Identify the Least Stable Compound
To find the least stable compound, we look for the highest positive value of ΔHf. This is because a higher positive value means that more energy is required to form the compound, indicating instability.

### Conclusion
Based on the analysis, the product with the highest positive ΔHf value indicates that it is the least stable. Therefore, if the options provided include values like +30 kJ/mol, +60 kJ/mol, etc., the one with the highest positive value (e.g., +60 kJ/mol) would be the correct answer.

### Answer
The product with the highest positive heat of formation value indicates that it is the least stable.