1
For the reaction A B the following graph was obtained. The time required (in seconds) for the concentration of A to reduce to 2.5 g L-1 (if the initial concentration of A was 50 g L-1) is . (Nearest integer) Given : 2 = 0.3010 [figure]
Answer
43
Solution
From the graph:
40 → 20 g L-1 between 5 s and 15 s, i.e. in 10 s;
30 → 15 g L-1 between 10 s and 20 s, i.e. in 10 s;
20 → 10 g L-1 between 15 s and 25 s, i.e. in 10 s.
the half-life is constant (independent of concentration), the reaction is of first order with t1/2 = 10 s.
k = 2.303 2t1/2
For first order: t = 2.303k [A]0[A]
t = t1/2 502.5 2
= 10 200.3010
= 10 1.30100.3010
= 43.2 s 43 s
Answer: 43
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