1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

General Chemistry questions and kinetics

  1. Sep 26, 2007 #1
    1. The problem statement, all variables and given/known data
    The initial concentration of reactant in a first-order reaction is 0.75M. The rate constant for the reaction is 2.75/s. What is the concentration (mol/L) of reactant after 6.5s?


    2. Relevant equations

    -kt=[A]initial/[A]anytime



    3. The attempt at a solution

    -(2.75/s)(6.5s)=[0.75M]/[A]@6.5seconds

    -17.875/1=0.75M/x; x= -4.20x10^-2; The answer to this problem is not right, but I do not have any idea how to go about it another way.

    Problem 2.

    The usefulness of radiocarbon dating is limited to 50,000 years. Show mathematically why this is true. (Hint: Remember half life follows first order kinetics. The half life of C-14 is 5.73 x 10^3 years).

    Half life formula : t1/2= 0.693/k
    Common integrate rate law for first order reactions: ln[A]=-kt + ln[A@ initial]
    5.73x10^3 = 0.693/k, k = 1.21x10^-4/s

    How would I use k in my integrated formula to prove that the half life is limited to 50,000 years?
     
  2. jcsd
  3. Sep 27, 2007 #2

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    #1. You have the wrong rate equation for a first-order reaction. Look at the rate equation you've used in #2. That's the one you need to use here.

    #2. What is (roughly) the relative abundance of C-14 (w.r. to C-12) in the atmosphere? Assume you have a sample that has about 1kg of C. How much of that would have been C-14, when the organism was alive? How much of that C-14 will be present in the sample today (use the rate equation to find this)?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: General Chemistry questions and kinetics
  1. Chemistry kinetics (Replies: 1)

Loading...