Concentration Changes Over Time

AP Chemistry· difficulty 2/5

A first-order reaction shows successive half-lives of 80 s on a [A] vs t plot.

t1/2 2 t1/2 First-order decay

For a first-order reaction, the half-life t1/2 = 80 s. After 240 s, what fraction of A remains?

  • A

    1/3

  • B

    1/8

    check_circle
  • C

    1/16

  • D

    1/4

Explanation

240 s = 3 half-lives. (1/2)^3 = 1/8 remains.

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