Half Life of a Reaction

Question

Calculate the number of half lives it takes for a

substance to reach 3.13% of it’s original concentration.

Calculate the rate constant for the first-order decomposition

of hydrogen peroxide in water at 40.0 °C, with a half life of

2.16 𝑥 104 seconds.

Calculate the half life in seconds for a second order reaction that

has a k = 3.44 𝑥 10−6𝑀−1𝑠−1 and reactant with an initial

concentration of 0.111 M.

Calculate the final concentration of a reactant for a zero order

reaction that has a half life of 3.27 minutes and an initial

concentration of 0.0465 M after 5.00 minutes have passed.

Answer 1

.0313 = e^rt

.5 = e^rt

ln.5 = rt

t = ln.5/r = half life

let x= number of half lives to reach 3.13% of the original amount

.0313 = e^(rt)= e^r(xln.5/r) = e^xln.5=

ln.013 = xln.5

x = ln.013/ln.5 = about 4.9977

= about 5 half lives to reach 3.13%