A certain first-order reaction a > b is 25% complete in 42 min at 25Â

1.	A certain first-order reaction a > b is 25% complete in 42 min at 25Â°c. What is its rate constant?
Answer» $6.19\times 10^{-3} min^{-1}$ Answer: RATE CONSTANT is Explanation: For First order REACTION, the expression for rate constant is: $k= \frac{2.303}{t}log\frac{a}{a-x}$ k= rate constant t= TIME REQUIRED for a reaction a= initial concentration x= amount of reactant decomposed in time t a-x= amount of reactant left after time t If initial concentration (a) = 100 As 25% of the reactant has decomposed, x=25 (a-x)= (100-25) = 75 Putting in the values we get $k= \frac{2.303}{42}log\frac{100}{75}$ $k=6.19\times 10^{-3} min^{-1}$