Question

The rate of reaction A \[ \to \] products is 10 mole/lit/min at time (\[{{\text{t}}_{\text{1}}}\])=2 min. What will be the rate in mol/lit/min at time (\[{{\text{t}}_2}\])=12 min?
 A . More than 10
 B . 10
 C . Less than 10
 D. 20

Answer 1

Hint: The reaction A \[ \to \] products. is a first order reaction. The rate equation of first order reaction is \[{\text{r = k}}\left[ {\text{A}} \right]\]. Where, rate is r, rate constant is k and \[\left[ {\text{A}} \right]\] is concentration of reactant A at a time t. The unit of rate depends upon the concentration of reactant and rate constant.

Complete step by step solution:
The definition of rate of a reaction is the speed of a reaction by which the concentration of reactants decreases and the concentrations of products increases per unit time.
This rate of a reaction can be expressed in terms of concentration of reactants or products. The magnitude of the rate value does not depend upon the way of expression ( by reactant or product). For reactants the rate shows as negative as throughout the reaction the concentration of the reactant decreases. On the other hand, the rate for the product shows as positive as the concentration of the product increases throughout the reaction.
Now the factors which affect the rate of a reaction is concentration of reactants or product, temperature, surface area of solid surface, pressure, and catalyst only.
Therefore, the rate of a reaction does not depend upon the time(t). it will be constant at any time. The rate depends upon the change of concentration per unit time.

So, the correct answer is B.

Note: Remember that rate of a reaction is the speed of a reaction by which the concentration of reactants decreases and the concentrations of products increases per unit time. The factors which affect the rate of a reaction is concentration of reactants or product, temperature, surface area of solid surface, pressure, and catalyst only.