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For a reaction 1/2 A → 2B, rate of disappearance of ‘A’ is related to the rate of appearance of ‘B’ by the expression

1. −d[A]/dt = 1/2 d[B]/dt
2. −d[A]/dt = 1/4 d[B]/dt
3. −d[A]/dt = d[B]/dt
4. −d[A]/dt = 4 d[B]/dt

Correct answer: −d[A]/dt = 1/4 d[B]/dt

Solution

Rate = -(1/(1/2)) d[A]/dt = (1/2) d[B]/dt, so -2 d[A]/dt = (1/2) d[B]/dt, giving -d[A]/dt = (1/4) d[B]/dt.

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