Question

Which is correct for a first order reaction

• A. The degree of dissociation is equal to $(1-e^{-kt})$
• 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)

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