For the reaction ` A + 3B to C + D ` rate of reactions ` prop [A][B]`

Answer

To determine whether the statement "the rate of reaction is proportional to [A][B]" for the reaction \( A + 3B \rightarrow C + D \) is true or false, we can follow these steps:

### Step 1: Write the balanced chemical equation
The balanced chemical equation is:
\[ A + 3B \rightarrow C + D \]

### Step 2: Understand the concept of rate of reaction
According to the law of mass action, the rate of a reaction is directly proportional to the product of the concentrations of the reactants, each raised to the power of their respective stoichiometric coefficients.

### Step 3: Apply the law of mass action to the given reaction
For the reaction \( A + 3B \rightarrow C + D \):
- The stoichiometric coefficient of \( A \) is 1.
- The stoichiometric coefficient of \( B \) is 3.

Thus, the rate of the reaction can be expressed as:
\[ \text{Rate} \propto [A]^1 \cdot [B]^3 \]

### Step 4: Write the rate law expression
The rate law expression based on the stoichiometry of the reaction is:
\[ \text{Rate} = k[A]^1[B]^3 \]
where \( k \) is the rate constant.

### Step 5: Compare with the statement
The statement claims that the rate of reaction is proportional to \([A][B]\). However, from our derived rate law, we see that:
\[ \text{Rate} \propto [A][B]^3 \]
This indicates that the rate is not simply proportional to \([A][B]\) but rather to \([A]\) and \([B]\) raised to their respective powers based on stoichiometry.

### Conclusion
Since the statement does not accurately reflect the relationship derived from the law of mass action, we conclude that the statement is **false**.