Question

HW10, S2. 2,4-Dichlorophenoxyacetic acid (24-D, MW = 221 g/mol) is the top-sale lawn weed killer. A bag of weed-control fertilizer has a label indicating a 24-D content of 0.25% (based on mass). It is also know that the “pure” 24-D contains 10 ppm of dioxins.

c. Assuming that the degradation of 24-D on a backyard lawn treated with 40 kg is a first order reaction with its half-life t1/2 = 11 days at 22°C, if we also know that for 24-D, t1/2 = 30 days at 5°C, calculate the activation energy (Ea) for the degradation of 24-D.

Answer 1

given data :

2,4-Dichlorophenoxyacetic acid degradation is a first order reaction .

answer :

we know that for first order reaction, half life equation,

so at 22 C,

= 0.063 day^-1

so at 5 C,

now for calculation of activation energy, we use arrhenius equation

summary :

here, we can find the rate constant K using first order half life equation.

after that we use arrhenius equation to find activation energy.

activation energy = 40238.7 J/mol