Question

A first-order reaction is carried out with an initial concentration of $10$ mole per litre and $80$% of the reactant changes into the product. Now if the same reaction is carried out with an initial concentration of $5$ mol per litre, the percentage of the reactant changing to the product is:

• A. $40$
• B. $80$
• C. $160$
• D. $\text{cannot be calculated}$

Answer 1

The correct option is B $80$

For a first order reaction time required to complete a definite fraction is independent of initial concentration.
Hence, the percentage of the reactant changing to the product is 80% irrespective of the initial concentration whether it is 10 mole per litre or 5 mole per litre.