Answer: Number of half lives occurred 2.
Explanation:
Let the initial concentration be x
Concentration left=25 % of the x= \(x\frac{25}{100}=\frac{x}{4}\)
To calculate the number of half lives, we use the formula:
\(a=\frac{a_o}{2^n}\)..(1)
where,
a = amount of reactant left after n-half lives = 0.0495 moles
\(a_o\) = Initial amount of the reactant = 0.7924 moles
n = number of half lives
\(\frac{x}{4}=\frac{x}{2^n}\)
taking log both sides
\(\logx-\log4=\logx-n\log2\)
\(\log4=n\log2\)
\(\log(2)^2=2\log2=n\log2\)
n = 2
Number of half lives occurred 2.
