Question:medium

For a reaction, the rate law is given by \( \text{rate} = k[A]^2[B] \). If the concentration of \( A \) is doubled and the concentration of \( B \) is halved, how will the rate of the reaction change?

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The rate of a reaction depends on the concentrations of the reactants raised to the powers specified by the rate law. Always use the correct exponents and factor in how concentration changes affect the rate.
Updated On: Nov 26, 2025
  • The rate will be doubled.
  • The rate will be halved.
  • The rate will be quadrupled.
  • The rate will remain unchanged.
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The Correct Option is C

Solution and Explanation

The rate law for the given reaction is: \[ \text{rate} = k[A]^2[B] \] Where: - \( k \) is the rate constant, - \( [A] \) and \( [B] \) are the concentrations of reactants \( A \) and \( B \). Given that the concentration of \( A \) is doubled and the concentration of \( B \) is halved, let the initial concentrations of \( A \) and \( B \) be \( [A]_0 \) and \( [B]_0 \), respectively. The new concentrations are: \[ [A] = 2[A]_0 \quad \text{and} \quad [B] = \frac{1}{2}[B]_0 \] Substituting these into the rate law yields: \[ \text{new rate} = k(2[A]_0)^2\left(\frac{1}{2}[B]_0\right) \] \[ \text{new rate} = k \times 4[A]_0^2 \times \frac{1}{2}[B]_0 \] \[ \text{new rate} = 2k[A]_0^2[B]_0 \] Comparing the new rate to the original rate: \[ \text{rate} = k[A]_0^2[B]_0 \] The new rate is twice the original rate, which means the rate is quadrupled.
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