Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: GeLe5000 on November 27, 2014, 04:50:24 AM
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Hello everybody.
Does anyone know what kind of energy is at the origin of the heat produced by an exothermic chemical reaction?
I know that heat in an aqueous medium is the manifestation of molecular movement but what is the physical process that caused the acceleration of water and other molecules?
In an exothermic reaction, the sum of the bond enthalpies of the reactants is less than the sum of the bond enthalpies of the products. The reactants are thus less stable than the products and more reactive; the reaction proceeds spontaneously from left to right and there's an excess of energy liberated in the environment.
For example, the neutralization of NaOH by HCl produces H2O and it's an exothermic reaction. Thus a hydroxyl ion captures a proton with the formation of a water molecule. What happens physically during this process that could lead to an increase in the speed of molecules?
Another example: the heat of combustion of cyclopropane is higher than for non-cyclic propane because of an excess of energy ("strain energy") present in cyclopropane. How can this excess of energy be transformed into molecular kinetic energy.
Is it possible that in both examples, electromagnetic waves are produced, photons of weak energy like microwaves or infrared because of the movements of electron towards lower energy orbitals?
Thank you for your comments.
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Please remember molecule energy is not limited to the movement of the molecules in an external frame. Also things that are internal to the molecule - rotations, vibrations - are part of the mechanical energy.