Question

Write any two characteristics of first order reaction.

Answer 1

In the first-order reaction, the reaction rate is dependent on the concentration of only one reactant. While writing characteristics for first-order reaction one can explain the reaction rate, unit for the reaction, and its dependence on the initial reaction concentration.

Complete step by step answer:

1. First of all we will discuss in detail the first-order reaction meaning. The first-order reaction is the reaction in which the rate of reaction is dependent only on the concentration of one reactant species irrespective of the increase in the concentration of other reactants.
2. Now let us discuss in detail the characteristics of the first-order reaction,
   i) The unit of the rate constant of the first-order reaction is ${\operatorname{Sec} ^{ - 1}}$ and we calculated this as below,
   The formula for the rate constant for the first-order reaction is,
   ${k_1} = \dfrac{{rate}}{{\left( {a - x} \right)}}$
   Now let us put the units of rate and $\left( {{\text{a - x}}} \right)$ as below,
   ${k_1} = \dfrac{{mol \cdot li{t^{ - 1}}{{\sec }^{ - 1}}}}{{mol \cdot li{t^{ - 1}}}}$
   In the above equation both the common factors $mol \cdot li{t^{ - 1}}$ will cancel out and we get the final unit as,
   ${K_1} = {\sec ^{ - 1}}$
   ii) In a first-order reaction when the concentration of a reactant (on which the rate is dependent) is increased by the ‘n’ factor then the rate of reaction will also increase by the ‘n’ factor. That means the change in concentration of reactant is directly proportional to the change in the rate of reaction.

Note:
As in the first-order reaction, the concentration of reactant directly affects the rate of reaction, the graph plotted between the concentration of reactant and time is always a straight line. This straight-line graph indicates the reaction is first order and that trick can be used to solve many graph-related problems.