Notices
Results 1 to 8 of 8
Like Tree1Likes
  • 1 Post By PhDemon

Thread: strongest endothermic reactions

  1. #1 strongest endothermic reactions 
    New Member
    Join Date
    Feb 2014
    Posts
    3
    I am doing a little independent research, and I am having a hard time finding an answer to this question. I want to know what some of the reactions are that absorb the most heat possible from their surroundings. I can find lists of exothermic reactions pretty easily, but for some reason it is tough to find the endothermic ones. If possible I would prefer to know the reactants, with the amount of energy absorbed. I would much appreciate any help I could get on finding this information.


    Reply With Quote  
     

  2.  
     

  3. #2  
    Bullshit Intolerant PhDemon's Avatar
    Join Date
    Feb 2013
    Location
    Newcastle-upon-Tyne, UK
    Posts
    5,600
    I don't have a specific answer but I can give you some pointers on the type of process to look for.

    Whether a chemical reaction is thermodynamically spontaneous or not depends upon the change in Gibbs free energy during a reaction. For a reaction to occur spontaneously this must be negative.



    where is the change in enthalpy, the change in entropy and T the temperature.

    If a reaction is endothermic the term is positive and so for the reaction to be spontaneous this means must be positive and large enough to offset the positive term. For these calculations the T is constant (at the starting temperature of the reaction) so must be positive and large enough to offset . The easiest way to have a reaction with a large is to create a lot of gas from solid or liquid reactants (the entropies of gases are much larger than those of liquids and solids leading to large values). So look for reactions of this type and calculate the and for the reactions. As Gibbs free energy, enthalpy and entropy are all state functions you can do this using Hess's Law. http://en.wikipedia.org/wiki/Hess's_law


    Last edited by PhDemon; February 1st, 2014 at 10:01 PM. Reason: fixed tex tags
    KJW likes this.
    Reply With Quote  
     

  4. #3  
    Forum Sophomore
    Join Date
    Jan 2014
    Posts
    106
    Some of the most commonly accessible endothermic reactions are the dissolution of salts in water. Ammonium chloride is a common example. Other things heat up when you dissolve them in water, like sodium hydroxide for example. You can look at a list like this one to see the relative heating and cooling effects of a range of compounds.

    http://sites.chem.colostate.edu/dive...ectrolytes.pdf
    Reply With Quote  
     

  5. #4  
    Bullshit Intolerant PhDemon's Avatar
    Join Date
    Feb 2013
    Location
    Newcastle-upon-Tyne, UK
    Posts
    5,600
    Yes but endothermic dissolution reactions are not very endothermic. I was trying to point you in the direction you asked for.

    EDIT: Apologies to Warron but I thought he was the same poster as Mr. Warren who made the OP.
    Reply With Quote  
     

  6. #5  
    Forum Sophomore
    Join Date
    Jan 2014
    Posts
    106
    Easy mistake

    I don't think that there are too many spontaneous endothermic reactions. The most commonly quoted one seems to be the reaction of barium hydroxide octahydrate with ammonium thiocyanate, described here.

    Endothermic Reaction - UW Dept. of Chemistry

    As someone else has commented:

    "Most endothermic reactions have to be driven by some external force, much as work has to be done to roll a boulder uphill."
    Reply With Quote  
     

  7. #6  
    New Member
    Join Date
    Feb 2014
    Posts
    3
    Thank you for the help. Specifically I was trying to think of a way to use an endothermic reaction to reduce the energy output of an exothermic reaction, and crunch some numbers. This was merely an Idea I had, and was thinking of possibilities of controlling extremely power full exothermic reactions by using a power full endothermic reaction. I could not find much written on this topic. I was just curious for my own knowledge.
    Reply With Quote  
     

  8. #7  
    KJW
    KJW is online now
    Forum Professor
    Join Date
    Jun 2013
    Posts
    1,734
    Quote Originally Posted by Mr. Warren View Post
    Thank you for the help. Specifically I was trying to think of a way to use an endothermic reaction to reduce the energy output of an exothermic reaction, and crunch some numbers. This was merely an Idea I had, and was thinking of possibilities of controlling extremely power full exothermic reactions by using a power full endothermic reaction. I could not find much written on this topic. I was just curious for my own knowledge.
    In that case, you're not limited by the constraint of exergonic reactions mentioned above. What you need to do is couple the reactions together. But you need to be specific about the reactions.
    There are no paradoxes in relativity, just people's misunderstandings of it.
    Reply With Quote  
     

  9. #8  
    exchemist
    Join Date
    May 2013
    Location
    London
    Posts
    3,779
    Quote Originally Posted by Mr. Warren View Post
    Thank you for the help. Specifically I was trying to think of a way to use an endothermic reaction to reduce the energy output of an exothermic reaction, and crunch some numbers. This was merely an Idea I had, and was thinking of possibilities of controlling extremely power full exothermic reactions by using a power full endothermic reaction. I could not find much written on this topic. I was just curious for my own knowledge.
    I suppose it's cheating a bit, but wouldn't phase changes such as evaporation or melting have these characteristics?
    Reply With Quote  
     

Similar Threads

  1. Replies: 2
    Last Post: January 24th, 2011, 11:41 PM
  2. Endothermic Reactions
    By Cold Fusion in forum Chemistry
    Replies: 0
    Last Post: July 3rd, 2010, 09:54 PM
  3. Strongest shape made from paper.
    By Gmano in forum Mechanical, Structural and Chemical Engineering
    Replies: 3
    Last Post: July 2nd, 2009, 03:34 AM
  4. Exothermic and Endothermic reactions
    By Bigbear in forum Chemistry
    Replies: 11
    Last Post: March 29th, 2008, 10:09 AM
  5. exothermic and endothermic reactions
    By almirza in forum Chemistry
    Replies: 3
    Last Post: April 11th, 2006, 01:41 AM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •