Solutions A and B are both clear and colourles. When solution A is mixed with solution B, the temperature of the mixture increases and a yellow precipitate is observed. What can be concluded from these observations?

Options

A. The reaction is thermodynamically favoured ( spontaneous) at all temperatures
B. The reaction is thermodynamically favoured ( spontaneous) only athigh temperature
C. The reaction is thermodynamically favoured ( spontaneous) only at low temperature
D. The reaction is not thermodynamically favoured ( spontaneous) at any temperature.

Explanation

To analyze the observations from the mixing of solutions A and B, we can follow these steps:

### Step 1: Identify the Observations
- Solutions A and B are both clear and colorless.
- Upon mixing, the temperature of the mixture increases.
- A yellow precipitate is formed.

### Step 2: Analyze the Temperature Change
- The increase in temperature indicates that heat is being released during the reaction. This suggests that the reaction is exothermic.
- In thermodynamics, an exothermic reaction is characterized by a negative change in enthalpy (ΔH < 0).

### Step 3: Analyze the Formation of the Precipitate
- The formation of a yellow precipitate indicates that a new solid phase has formed from the reaction of solutions A and B.
- The formation of a precipitate generally signifies a decrease in the randomness (entropy) of the system, leading to a negative change in entropy (ΔS < 0).

### Step 4: Apply Gibbs Free Energy Equation
- The spontaneity of a reaction can be determined using the Gibbs Free Energy equation:
\[ ΔG = ΔH - TΔS \]
- Since ΔH is negative (exothermic) and ΔS is also negative (due to the formation of the precipitate), the sign of ΔG will depend on the temperature (T).

### Step 5: Determine Conditions for Spontaneity
- At low temperatures, the term \(TΔS\) (which is positive because ΔS is negative) will be smaller than ΔH (which is negative), making ΔG negative. Therefore, the reaction is thermodynamically favored at low temperatures.
- At high temperatures, the \(TΔS\) term may become larger than ΔH, leading to a positive ΔG, which means the reaction would not be spontaneous.

### Conclusion
From the observations and analysis, we can conclude that:
- The reaction is thermodynamically favored only at low temperatures.

### Final Answer
The correct conclusion is that the reaction is thermodynamically favored only at low temperatures.