Question

A first-order reaction has a rate constant of $1.5/minutes$.
What fraction of the reactant B remains after $1.848$ minutes?

• A. One half
• B. One fourth
• C. One eighth
• D. One sixteenth
• E. None of the above

Answer 1

Answer: (D)

One sixteenth

Since we know that for first order reaction
rate constant $k=\frac{2.303}{t}\log \frac{A_0}{A}$
$⟹t=\frac{2.303}{k}\log \frac{A_0}{A}$
$⟹1.848=\frac{2.303}{1.5}\log \frac{A_0}{A}$
$⟹\log \frac{A_0}{A}=\frac{1.848\times 1.5}{2.303}$
$⟹\log \frac{A_0}{A}=1.2$
$⟹\frac{A_0}{A}=16$
$⟹\frac{1}{x}=16$
$⟹x=\frac{1}{16}$