halflife

  1. S

    Mysterious half-life problem

    The problem says, "carbon dating may be used to date materials between 100 and 40,000 years old. The half-life of the first order decay of carbon 14 isotope is 5730 years. What percentage (=[C14]f/[C14]i) of carbon 14 remains in a sample after 40,000 years?" I easily found k but couldn't decide...
  2. L

    Half-Life question help me please !

    A isomerises to form B. The reaction is first order. If 75% of A is converted to B in 2.5 hours, what is the half- life for the isomerism? I know the answer is 1.25 hours but I don't know how or why? My maths is pretty bad for a chem student and when it comes to simple maths, i stuggle as it...