Question

The rate of reaction, A + B $\rightarrow$ Products, is given by the equation, $r = k[A][B]$. If $B$ is taken in large excess. the order of reaction would be

• A. 2
• B. 1
• C. zero
• D. unpredictable

Answer 1

Answer: (B)

1

Answer 2

The rate law is $r = k[A][B]$. When B is in large excess, its concentration effectively remains constant. The rate equation simplifies to $r = k'[A]$, where $k' = k[B]_{\text{excess}}$ is a new constant. This shows the reaction is pseudo-first-order with respect to A, making the observed order 1.