Question

The order for the given reaction is:
$A + 2B \rightarrow Products$
$Rate = k[A]^{\frac{1}{2}}[B]^1$

• A. 1.5
• B. 1
• C. 0.5
• D. 2

Hint:

Order = Sum of powers in the rate law. Do not use the coefficients from the balanced reaction equation.

Answer 1

The Correct Option is A

Step 1: Concept
The overall order of a chemical reaction is defined strictly by the experimentally determined rate law.

Step 2: Meaning
It is mathematically calculated as the sum of the exponents (powers) of the concentration terms present in the rate law equation.

Step 3: Analysis
The experimentally determined rate law is: \[ \text{Rate}=k[A]^{1/2}[B]. \] The exponent of $[A]$ is $\frac{1}{2}$ and the exponent of $[B]$ is $1$. Therefore, the overall order of the reaction is: \[ \text{Overall Order} =\frac{1}{2}+1 =\frac{3}{2}=1.5. \]

• The order of a reaction is determined from the experimentally obtained rate law.

• The given rate law is: \[ \text{Rate}=k[A]^{1/2}[B]. \]

• The order with respect to reactant $A$ is equal to the exponent of its concentration: \[ \boxed{\frac{1}{2}}. \]

• Similarly, the order with respect to reactant $B$ is: \[ \boxed{1}. \]

• The overall order of the reaction is obtained by adding the exponents of all reactants: \[ \text{Overall Order} =\frac{1}{2}+1 =\frac{3}{2}. \]

• Hence, \[ \boxed{\text{Overall Order}=1.5.} \]

• Since the reaction order is fractional, it indicates that the reaction mechanism is more complex and cannot be inferred directly from the balanced chemical equation.

Step 4: Conclusion
The stoichiometric coefficients in the balanced chemical equation ($A + 2B$) are entirely irrelevant; only the rate law exponents dictate the order.

Final Answer: (A)