Chem 2

The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentration.

a) How long will it take for 10% of the U-238 atoms in a sample of U- 238 to decay?

b)If a sample of U-238 initially contained 1.9×1018 atoms when the universe was formed 13.8 billion years ago, how many U-238 atoms will it contain today?

asked by Kristina
  1. k = 0.693/t1/2
    Then
    ln(No/N) = kt
    I would call No = 100
    Then N = 90(after 10 have decayed--which is 10%)
    k from above. Solve for t in years.

    b.
    Same procedure. No = atoms you started with. N = atoms remaining.

    posted by DrBob222
  2. hb

    posted by Anonymous
  3. 100

    posted by Anonymous

Respond to this Question

First Name

Your Response

Similar Questions

  1. chem

    Pu-238 is radioactive by alpha-decay (half-life 87.7 y). Each decay releases 5.6 MeV of energy. Pu-238 is sometimes used to power space probes. If all the decay energy can be converted to electric power, what mass of Pu-238 would
  2. Chemistry

    Pu-238 is radioactive by alpha-decay (half-life 87.7 y). Each decay releases 5.6 MeV of energy. Pu-238 is sometimes used to power space probes. If all the decay energy can be converted to electric power, what mass of Pu-238 would
  3. Earth Science

    1. We start with 400 atoms of Uranium-238. How many remain after 4.5 billion years? _______ After 9 billion years? _______ After 13.5 billion years? ________ 2 . How long will it take for ½ of the original amount of Rubidium-87
  4. Calculus

    The rate of decay is proportional to the mass for radioactive material. For a certain radioactive isotope, this rate of decay is given by the differential equation dm/dt = -.022m, where m is the mass of the isotope in mg and t is
  5. Math - D.E.Q.

    The half-life of a radioactive isotope is the amount of time it takes for a quantity of radioactive material to decay to one-half of its original amount. i) The half-life of Carbon 14 (C-14) is 5230 years. Determine the decay-rate
  6. Chemistry

    Uranium-238 has half life of 4.51 * 10^9 years Uranium-234 has half life of 2.48 * 10^5 years Thorium-230 has half life of 8.0 * 10^4 years Radium-226 has half life of 1.62 * 10^3 years Lead-210 has half life of 20.4 years. The
  7. chemistry

    Some radioactive nuclides have very short half-lives, for example, I-31 has a half-life of approximately 8 days. Pu-234, by comparison has a half-life of 24,000 years. Explain why both of these examples are dangerous, even though
  8. geology

    How old are the oldest meteorites yet studied and what is the minimum age of Earth since Earth is at least as old as the meteorites. We know the oldest meteorites contain equal amounts of uranium 238 and lead 206. Uranium 238 has
  9. Chemistry

    Geologists can estimate the age of rocks by their uranium-238 content. The uranium is incorporated in the rock as it hardens and then decays with first-order kinetics and a half-life of 4.5 billion years. A rock is found to
  10. Chemistry 1046

    Geologists can estimate the age of rocks by their uranium-238 content. The uranium is incorporated in the rock as it hardens and then decays with first-order kinetics and a half-life of 4.5 billion years. A rock contains 65.7% of

More Similar Questions