A certain first-order reaction (A rightarrow products) has a rate constant of 3.

Question

A certain first-order reaction (A rightarrow products) has a rate constant of 3.00 times 10^-3 s^-1 at 45 degree C. How many minutes does it take for the concentration of the reactant, [A], to drop to 6.25% of the original concentration? Express your answer with the appropriate units. 1.5 min Part B A certain second-order reaction (B rightarrow products) has a rate constant of 1.45 times 10^-3 M^-1 middot s^-1 at 27 degree C and an initial half-life of 264 s. What is the concentration of the reactant B after one half-life? Express your answer with the appropriate units. _________ ___________

Explanation / Answer

(A)

For a first order reaction rate constant , k = ( 2.303 /t )x log ( Mo / M)

Where

Mo = initial concentration = 100

M= concentration after time = 6.25

K = rate constant = 3.00x10-3 s-1

t = time = ?

Plug the values we get

t = ( 2.303 /k )x log ( Mo / M)

= 924.4 s

= 924.4 s x 1 min / 60s

= 15.4 min

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