Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I need some freakin help with this half-life problem

  1. Mar 4, 2007 #1
    The uncoiling of DNA is a first order process with an activation energy of 430 kJ/mole. At 60oC, the half-life is estimated to be 2 minutes.
    a. Write a chemical equation that represents this reaction. Then, write the rate law for this reaction.
    b. Calculate the half-life at normal body temperature, 37 oC.
    c. What is the chemical force that holds the DNA in its coiled state? Is the uncoiling of DNA favored by enthalpy or entropy or both? Give reasons.
    d. Is the uncoiling of DNA spontaneous at 37 oC? Give reasons.
    e. Draw a reaction energy diagram for the uncoiling of DNA.

    here are some simple directions, b is the probelm im doing,
    i got some formulas but i dont know which one ill use, im just confused with this, may u give me a hint or some information so i can figure this problem out, ill work and the problem and post it up in a bit
  2. jcsd
  3. Mar 4, 2007 #2
    what equation shall i use, .693/k or 1/k[A] with a little o at the bottom right
  4. Mar 4, 2007 #3
    ok i am suuppost to use the .693/k since this reaction is a first order reaction
  5. Mar 4, 2007 #4
    here's what i figured out, k = A e-Ea/RT

    so i took the half life equation .693/k and changed it to .693/Ae -Ea/RT
  6. Mar 4, 2007 #5
    i plugged in my numbers which were .693/ Ae -430kj/mole / (8.1314 J / mole. K) ( 310 K)

    i think im doing it right but how do i figure out Ae
  7. Mar 4, 2007 #6
    or what is Ae
  8. Mar 4, 2007 #7
    ok what is A because e is apart of the -Ea/RT
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook