The mathematical expression which describes the reaction rate in terms of molar concentrations of the reactants as determined experimentally is called rate law. The sum of the coefficients of the reacting species that are involved in the rate equation of a particular reaction is known as the order of the reaction, The reactions may be classified as first, second and third order reactions depending upon the number of of reacting species involved in the rate equation. It can be fractional in complex reations and even zero in certain reactions such as photochemicla reactions. The units of the rate constant(k) can help ini predicting the nature of a particular reaction.
1) A substance decomposes in a solution followig first order kinetics. Flask A contains 1L of 1M solution and flask B has 100 mL of 0.6 M solutions. After 8 hours, the concentrations of substance in flask A becomes 0.25 M. What will be the time taken for the concentration of the same substances in flask B to becomes 0.3 M?

Options

A. `0.4` hr
B. `2.4`hr
C. `4.0` hr
D. unpredictable as rate constant is not given.

Answer

C

Explanation

c) In flask A:
`k=(2.303)/8 log 1.0/(0.25) =2.303/4 log2`
In flask B:
`t=2.303/k log 0.6/0.3 = (2.303 xx 4)/(2.303) = 4`
Log 2 cancels out