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The half-life of a first-order decomposition reaction is 0.50 hours If the initi

ID: 500057 • Letter: T

Question

The half-life of a first-order decomposition reaction is 0.50 hours If the initial concentration of reactant is 0.52 what is the concentration of reactant after 752 seconds? What is the rate constant for a first-order reaction with half life of 100. seconds? Given the initial rate data for the reaction A + B rightarrow C (a) calculate the respective orders of reaction for reactants A and B. What is the overall order for the reaction? (b) Calculate the rate constant, k, for this reaction. (c) Write the complete rate expression for this reaction.

Explanation / Answer

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

Where

Mo = initial concentration = 0.52 M

M = concentration left after time t = ?

K = rate constant = 0.693 /t1/2 = 0.693/0.5 hr-1 = 1.386 hr-1

t = time = 752 s = 752 s x (1min /60s) x ( 1 hr/60 min) = 0.209 hr

Plug the values we get

log ( Mo / M) = (kt)/2.303 = 0.16

( Mo / M) = 100.126 = 1.336

M = 0.390 M

(2) K = rate constant = 0.693 /t1/2 = 0.693/100 s-1 = 6.93x10-3 s-1