Question

155.
The half life for the first order reaction
N,O, → 2NO, + 1/20, is 24 hrs. at 30°C. Startin
with 10g of N, O, how many grams of N, O,
remain after a period of 96 hours ?
(1) 1.25 g
(2) 0.63 g
(3) 1.77 g
(4) 0.5 g

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Answer 1

Answer:

Correct option is

B

0.63 g

For a 1st order reaction,

t1/2= 0.693/k (k=rate constant)

Therefore, k = 0.693/t1/2 = 0.693/24= 0.0289 hr-1

kt= 2.303*log(a/(a-x)) {a= initial amount, a-x= amount left}

0.0289*96 = 2.303*log(10/(10-x))

log(10/(10-x))= 1.2

10/(10-x) = antilog1.2

10/(10-x) = 15.85

10 = 158.5-15.85x

15.85x = 148.5

x= 9.36g

a-x = 10-9.36= 0.63g

Hence, option 2 is correct