Question

Which is correct for a first order reaction

• A. The degree of dissociation is equal to $\left(\right.1-e^{- k t}\left.\right)$
• B. A plot of reciprocal concentration of the reactant vs time gives a straight line
• C. The time taken for the completion of 75% reaction is thrice the $t_{1 / 2}$ of the reaction
• D. The pre-exponential factor in the Arrhenius equation has the dimension of time $T^{- 2}$

Answer 1

Answer: (A)

$\left(\right.A\left.\right)$ is correct because degree of dissociation $=1-e^{- k t}$ at any time t.
$\left(\right.B\left.\right)$ is wrong because plot of log [A] vs t is a straight line
$\left(\right.C\left.\right)$ is wrong because time taken for 75% reaction is two half life.
$\left(\right.D\left.\right)$ is wrong because in $k=Ae^{- E_{a} / R T}$ , $E_{a / R T}$ is dimensionless hence A has the unit of $K$ .