5 thoughts on “32. Monday, November 23, 2009”

1. Jason Todd December 1, 2009 at 6:34 pm

   Professor Knapp,

   Can you please post the video from November 23, I was unable to make it to class that day.

   Thank you
2. chem111-mjknapp Post authorNovember 30, 2009 at 8:40 pm

   Ahhhh, ATP.

   The reaction is actually exothermic, but you have to consider the other reactants:

   ATP +H2O –> ADP + P

   “ATP” is kinda like this” Adenine-O(PO2)-O(PO2)-O(PO2)-OH, where each O(PO2) group has a negative 1 charge (so the three phosphate groups of ATP has an overall -3 charge). To make ADP, you just add H-O-H across the final P-O-P bonds, which makes ADP and phosphate: [HO-(PO2)-OH]2-, also written as [H2PO4]1-. The net bonding change is to break these bonds:P-O and H-O; you make these: P-O and H-O. Although this looks like zero change in bond energy, it turns out the P-O bonds are not all of equal stability. The P-O bond is less stable in ATP due to the presence of so many negative charges in ATP, while the P-O bond in [H2PO4]1- is much more stable!
3. Andrew November 30, 2009 at 12:34 am

   Hmm I guess I just need to get it in my head that it takes energy to break a bond, and energy is released when one is formed.

   When I think of this situation, the first thing that comes to mind is ATP. When ATP breaks into ADP + P, energy is released, isn’t it? Is this an exception?
4. chem111-mjknapp Post authorNovember 28, 2009 at 11:50 am

   Hi Andrew,
   you’re half way there: energy is required to break the bonds of the reactants, and energy is released when you form bonds for the products. But there’s a mis-statement in your initial premise that is giving you fits. If you re-stated your premise, you’d be in good shape: “if weaker reactant bonds break to form stronger product bonds, the reaction is more exothermic.”
5. Andrew November 26, 2009 at 12:36 am

   I’m having trouble understanding this concept:

   Weaker product bonds forming stronger reactant bonds yields MORE exothermic reactions.

   This doesn’t make sense to me… Wouldn’t the energy in the broken product bonds need to be used to form the new bond?

   Can anyone help me conceptualize this?

   Thanks