Chemistry Reaction Kinetics UHS 2024
PMDC Verified Question 2 of 80
Consider the hypothetical equation:
\( a\text{A} + b\text{B} \longrightarrow c\text{C} + d\text{D} \)
Which of the following represents correct rate equation?
A
Rate = \( k[\text{A}][\text{B}] \)
B
Rate = \( k[\text{A}]^a[\text{B}]^b \)
C
Rate = \( k[\text{A}]^a \)
D
Rate = \( k[\text{B}]^2 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Rate = \( k[\text{A}]^a[\text{B}]^b \)
Concept:

According to the classical Law of Mass Action (often assumed for theoretical elementary reactions unless experimental data dictates otherwise), the rate is proportional to the product of active masses of reactants raised to their stoichiometric coefficients.

Formula:

$$ \text{Rate} = k[\text{Reactant 1}]^{\text{coef}_1}[\text{Reactant 2}]^{\text{coef}_2} $$

Solution:

  • The reactants are \( \text{A} \) and \( \text{B} \).
  • Their respective stoichiometric coefficients in the balanced theoretical equation are \( a \) and \( b \).
  • Assuming an elementary reaction profile, the coefficients become the exponents in the theoretical rate law.
  • Thus, the theoretically represented rate equation is: \( \text{Rate} = k[\text{A}]^a[\text{B}]^b \).


Why other options are incorrect:

Option A assumes all coefficients are 1. Options C and D ignore one of the reactants entirely.

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