Thread: What determines the form in which energy is released from a chemical reaction.

Chemical reactions/physical processes that are exothermic release energy as a mixture of different forms on energy: Light, heat, etc. For different reactions/under different conditions, the free energy can take different forms: light, thermal, sonic, electrical etc.

What are the factors that determine/influence what form the energy takes?
Can it be predicted with much accuracy or is empirical testing still the only way to find out?

I'm sure there must be some good links that explain this, but somehow the wording I was using for my search didn't find anything other than the usual explanation of what an exothermic reaction is and the forms that energy can take (but not why it takes one or another).

Originally Posted by Enkephalos

Chemical reactions/physical processes that are exothermic release energy as a mixture of different forms on energy: Light, heat, etc. For different reactions/under different conditions, the free energy can take different forms: light, thermal, sonic, electrical etc.

What are the factors that determine/influence what form the energy takes?
Can it be predicted with much accuracy or is empirical testing still the only way to find out?

I'm sure there must be some good links that explain this, but somehow the wording I was using for my search didn't find anything other than the usual explanation of what an exothermic reaction is and the forms that energy can take (but not why it takes one or another).

Well? What is it? Your own words only if you please.

Originally Posted by sigurdV

Originally Posted by Enkephalos

Chemical reactions/physical processes that are exothermic release energy as a mixture of different forms on energy: Light, heat, etc. For different reactions/under different conditions, the free energy can take different forms: light, thermal, sonic, electrical etc.

What are the factors that determine/influence what form the energy takes?
Can it be predicted with much accuracy or is empirical testing still the only way to find out?

I'm sure there must be some good links that explain this, but somehow the wording I was using for my search didn't find anything other than the usual explanation of what an exothermic reaction is and the forms that energy can take (but not why it takes one or another).

Well? What is it? Your own words only if you please.

Ok. An exothermic reaction is one where something is moving from a higher energy to a lower energy state (such as two chemicals forming or breaking bonds, certain ions dissolving in solution). There is potential energy contained in the starting state, which becomes free energy as the system moves to a lower energy state. The free energy that is released into the environment as a result of the the making/breaking of chemical bond etc can come out in various forms, such as light and heat. Different reactions differ in the form in which they release free energy to their surroundings. This free energy can take various forms, which vary depending on the specific reaction and the conditions it is carried out under: sometimes more is released as heat, sometimes more is released as light.
An exothermic reaction is the opposite of an endothermic reaction. An endothermic reaction captures free energy in the form of light or heat (some reactions being more effectively driven by one or the other under certain conditions) into potential energy (again, this can be the making or breaking of covalent bonds, ions dissolving in solution, among many others). I am just as curious about why light vs heat drive certain reactions more effectively as I am with the first question.

All exothermic chemical reaction releases its energy in the form of photon(energy) radiation.

This photon radiation have different wave length.
in the case of H2 gas burning with O2,
the wavelength of the photon emitted can be determined roughly by black body radiation.

H2 burning have a temperature of aroudn 3000 Kelvin
Adiabatic flame temperature - Wikipedia, the free encyclopedia

Based on that temperature, the visible wavelength emitted is on the red/orange region. However, the peak of the radiation occurs on the inra-red region.
Black-body radiation - Wikipedia, the free encyclopedia

Infra-Red radiation is expecially good in vibrating & spinning molecules.
So your skin molecules/other stuff vibrates rapidly due to absorbing this IR radiation.

Hence the classical definition of "heat"