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Exothermic / Endothermic

  1. Feb 25, 2007 #1
    Endothermic / Exothermic

    I have to say that I am a little at loss here. I understand that an endothermic process absorbs more energy than it releases, and that an exothermic process is the opposite. However, I don't understand the implications in terms of kinetic and potential energy. Here is what I have seized so far:

    - Breaking bonds requires energy (This is understandable)
    - Forming bonds releases energy (Why???)
    - In an exothermic reaction, the bonds of the products are stronger than those of the reactants.
    - In a endothermic reaction, it is the opposite.

    Now how exactly is energy transfered from potential to kinetic? If in a reaction, the temperature rises, is it endothermic or exothermic?
  2. jcsd
  3. Feb 25, 2007 #2
    Electrons form the bonds, and if the temperature in a reaction is increasing does that correspond to an increase in heat (release) or a decrease in heat (consumption)?
  4. Feb 25, 2007 #3
    Ok. But how is heat consumed exactly? When bonds get stronger, kinetic energy is transfered to atoms? I don't really get the logic, since if bonds get stronger, the more restraint atoms and thus would have less kinetic energy...
  5. Feb 25, 2007 #4
    Sounds like a lot of hand waving unless you have studied the quantum mechanics of the chemical bond (covalent).

    Heat is added to a reaction to overcome the activation energy, the lower the activation energy the more rapid the reaction, the higher the activation energy, the more slowly the reaction.
  6. Feb 25, 2007 #5
    Forming Bonds releases energy because bond formation is a stablizing process. Something is said to be more stable with respect to something else if the former has lower energy than the later. Everything in nature has to tendency to attain stability by lowering its energy this is done simply by releasing energy in some form (Heat or EM waves for instance).

    As discussed above the more stronger the bond, lower is its energy. Since energy is released in an exothermic process the energy of the reactants must be greater than the products (This difference is what that is released) or in other words the product is more stable than reactants which in turn means that product must be having stronger bonds than reacants

    Just the opposite of my previous answer.. :-)

    Atoms in a molecule are in the nuclear force field of other atoms, as such work has to be done by external agent in order to move atoms against the field and work is given to external agent when we move it closer. in this respect all atoms have some amount of energy due to the position it has with respect to other atoms. if we have to change the position some energy change has to occur, this happens in the form of work which in turn changes the state of motion of atoms (or kinetic energy).
  7. Feb 27, 2007 #6


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    Energy can be transferred as heat. The terms 'endothermic' and 'exothermic' pertain to changes in enthalpy, and enthalpy is defined as H=U+PV, where U is the internal energy, P is the pressure, and V is the volume. Heat and temperature and not equivalent to enthalpy. In actuality, the enthalpy concept is a bit complicating, it entails the steps that are required to create the system from a preliminary "standard" state.
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