When two reactants A and B are mixed to give products C and D, the reaction quotient (Q) at the initial stages of the reaction

Options

A. Is zero
B. Decreases with time
C. Is independent of time
D. Increases with time

Answer

To solve the question regarding the reaction quotient (Q) when two reactants A and B are mixed to form products C and D, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Reaction**: The reaction is given as:
\[ A + B \rightarrow C + D \]
Here, A and B are the reactants, and C and D are the products.

2. **Define the Reaction Quotient (Q)**: The reaction quotient (Q) is defined as the ratio of the concentrations of the products to the concentrations of the reactants at any point in time. It can be expressed as:
\[ Q = \frac{[C][D]}{[A][B]} \]
where \([C]\), \([D]\), \([A]\), and \([B]\) are the molar concentrations of the respective species.

3. **Initial Concentrations**: At the initial stage of the reaction (when the reactants are first mixed), we assume:
- The concentration of A is \(C_1\).
- The concentration of B is \(C_2\).
- The concentrations of products C and D are both zero, since the reaction has just started.

4. **Calculate Q at Initial Stage**: Substitute the initial concentrations into the expression for Q:
\[ Q = \frac{[C][D]}{[A][B]} = \frac{0 \times 0}{C_1 \times C_2} \]
Since the concentrations of C and D are zero, the equation simplifies to:
\[ Q = \frac{0}{C_1 \times C_2} = 0 \]

5. **Conclusion**: Therefore, at the initial stage of the reaction, the reaction quotient (Q) is equal to zero.

### Final Answer:
The correct answer is **Option A: 0**.