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irina irina
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Posts: 919
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11 years ago
Studying for the AP exam and can't figure out how to do these sorts of problems:

For a first order reaction with a rate constant k = 3.13 x 102 s-1, how long does it take for the concentration of the only reactant to become 40% of the original amount?
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#1
11 years ago
Since this is first order, our formula is:

Ln(Caf / Cai) = -(3.13 * 10^2 /s)*t

Where Caf is the final concentration and Cai is the initial concentration.

We want the time when Caf = 0.4*Cai, or Caf / Cai = 0.4

Ln(0.4) = -(3.13 * 10^2 /s)*t

t = 0.00293 s
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