Half-life equation for first-order reactions: t 1/2=0.693 k where t 1/2 is the h

Question

Half-life equation for first-order reactions:
t1/2=0.693k
where t1/2 is the half-life in seconds (s), and k is the rate constant in inverse seconds (s1).

Part A

What is the half-life of a first-order reaction with a rate constant of 4.30×104 s1?

Express your answer with the appropriate units.ANSWER:1610 s

Part B****HELP PLS

What is the rate constant of a first-order reaction that takes 173 seconds for the reactant concentration to drop to half of its initial value?

Express your answer with the appropriate units.

Part C ****HELP PLS

A certain first-order reaction has a rate constant of 7.40×103 s1. How long will it take for the reactant concentration to drop to 18 of its initial value?

Express your answer with the appropriate units.

Explanation / Answer

Part A

T1/2 = 0.693/k

     = (0.693/(4.3*10^(-4))

   T1/2 = 1611.63 Sec

Part B

K = 0.693/t1/2 = (0.693/173) = 4*10^(-3) S-1

Part C

K = 2.303/tlog(a/a-x)

7.4*10^(-3) = (2.303/t)*log(1/(1/8))

t = time = 281 sec

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