In a mixture of A and B, components show positive deviation when:

Options

A. (a) A-B interaction is stronger than A -A and B-B interaction
B. (b) A-B interaction is weaker than A-A and B-B interaction
C. (c) `/_\V"mix" lt0, /_\Smix gt0`
D. (d) `/_\V"mix" = 0, /_\Smix gt0`

Answer

To determine when a mixture of components A and B shows positive deviation, we need to analyze the interactions between the molecules of the components involved. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand Ideal and Non-Ideal Solutions
- **Ideal Solution**: In an ideal solution, the interactions between like molecules (A-A and B-B) are equal to the interactions between unlike molecules (A-B).
- **Non-Ideal Solution**: In a non-ideal solution, the interactions differ, leading to either positive or negative deviations.

### Step 2: Define Positive and Negative Deviations
- **Positive Deviation**: This occurs when the interactions between the molecules of the components (A-A and B-B) are stronger than the interactions between the different components (A-B).
- **Negative Deviation**: This occurs when the A-B interactions are stronger than the A-A and B-B interactions.

### Step 3: Analyze the Strength of Interactions
- For positive deviation, we can summarize:
- Strength of A-A and B-B > Strength of A-B
- This means that when A and B mix, they are less stable compared to when they are separate, leading to an increase in energy (positive ΔH).

### Step 4: Consider Enthalpy and Entropy Changes
- **Enthalpy Change (ΔH)**: For positive deviation, ΔH is positive because the mixture is less stable.
- **Entropy Change (ΔS)**: ΔS is generally positive for both positive and negative deviations, indicating an increase in randomness.

### Step 5: Evaluate Volume Change (ΔV)
- **Volume Change (ΔV)**: For positive deviation, ΔV is positive, indicating that the mixture occupies more volume than the sum of the individual components.

### Step 6: Review the Given Options
Now, let’s analyze the options provided in the question:
1. **AB interaction is stronger than AA or BB interaction**: This indicates negative deviation (incorrect).
2. **AB interaction is weaker than AA and BB interaction**: This indicates positive deviation (correct).
3. **ΔV mixture is less than zero**: This indicates negative deviation (incorrect).
4. **ΔV mixture is 0 and ΔS mixture is greater than 1**: This does not apply to positive deviation (incorrect).

### Conclusion
The correct condition for positive deviation in a mixture of components A and B is:
- **AB interaction is weaker than AA and BB interaction**.

### Final Answer
The correct answer is: **AB interaction is weaker than that of AA and BB interaction**.

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