Chemical Reactions Producing Light and Heat

In summary, chemical reactions produce light when there is a collision on the atomic scale which causes a change in energy state and the excess energy is shed in the form of a photon. This is also the case for heating up a coil of a filament lamp, where the high resistance causes the wire to heat up and emit electromagnetic radiation. The amount of light produced in a reaction depends on its energy and speed, and certain materials such as glow sticks and LEDs can emit light without producing significant amounts of heat. The emission of light is caused by electrons dropping from higher energy levels to lower ones, and the challenge is to produce enough energy for this without creating excess heat.
  • #1
Hi there,

I was just wondering about this point, why do some chemical reactions produce bright light (and even sound) whilst others do not?

For example: in the rapid oxidation of Magnesium in air after given the necessary activation energy, a bright white light is emitted. However, in many other chemical reactions, no light at all is produced.

What causes the light?

Also one other question: Why does heating up a coil of a filament lamp produce such a bright light? Why do some materials produce output different ratios of heat energy and light energy when current is passed through it?

Thanks.
 
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  • #2
This is caused by a collision on the atomic scale. In the case of a light bulb, the extremely high resistance of the filament wire increase the chance of a collision between the charged particles moving through the wire and the particles in the filament.

When the collision occurs, there is a change in energy state (can't remember if it happens once or twice) and it is the excess energy being shed that is a photon being emitted.

Can't really give much more than that as I'm not entirely sure myself and don't want to mislead if I'm incorrect.
 
  • #3
Any chemical reaction will result in a release of heat, which will cause whatever material to emit electromagnetic radiation (Which is what light is) at various frequencies depending on the temperature. Look up Black Body Radiation.

In general, chemical reactions that release more energy or react quicker will produce more light than those that are less energetic or slower reacting.

As for a light bulb, the filament has a high resistance to an electrical current. This causes it to heat up as a current is passed through it. Just like above, when something gets hot it emits electromagnetic radiation, AKA light. I believe that the light output solely depends on temperature, not the material. However, certain lights work a bit differently than a standard incadescant light bulb.
 
  • #4
Ok, so in any case that light is emitted, it is also a case in which heat is being emitted?

Is it possible to know the temperature of a compound based on the wavelength/intensity of the light?
 
  • #5
Most chemical reactions produce light because of heat. But not all. If you look at glow sticks, for example, they glow without being nearly hot enough to do so. Similar thing happens with fireflies. They wouldn't be able to survive the heat necessary to produce this light. LEDs are in the same category. There is no actual chemical reaction, but what happens to electrons in an LED is similar to what causes light emission in reactions with cold glow.

Anyways, the physics. Electrons in an atom occupy different energy levels. The actual energies depend on the nucleus of the atom, the number of electrons, and to a slightly lesser degree, on neighboring atoms. Electrons try to occupy the lowest energy states available, but there can only be two per state due to Pauli Exclusion. What's interesting is that there are ways to get electrons to higher energy states. One is to heat the material. Another is to hit the atom with something, like a free electron. Finally, there are some chemical reactions resulting in excited electrons.

When an electron at high energy level drops down to a lower energy level, it emits a photon that carries away the difference. That's the light you see from pretty much any light source.

The real trick is to have the energy needed to produce the visible light without allowing any significant amount of that energy to go into motion of the nuclei. Most reactions result in the two reacting molecules or nuclei to snap at each other like a pair of magnets that you let go of. That results in a lot of vibration and production of heat. Getting them to "snap" together gently, yet have enough energy to fling an electron to a high energy level is not a trivial task.
 

What is a chemical reaction producing light and heat?

A chemical reaction producing light and heat is a process in which energy is released in the form of light and heat as a result of a chemical reaction taking place between two or more substances.

What are some common examples of chemical reactions producing light and heat?

Some common examples of chemical reactions producing light and heat include combustion, bioluminescence, and chemiluminescence. Combustion is the chemical reaction that takes place when a fuel and an oxidizing agent react to produce heat and light. Bioluminescence is the production of light by living organisms, such as fireflies and certain marine animals. Chemiluminescence is the emission of light during a chemical reaction, such as in glow sticks.

How do chemical reactions produce light and heat?

Chemical reactions produce light and heat through the release of energy. This energy is usually in the form of heat, which is released as the chemical bonds between atoms in the reactants are broken and new bonds are formed. Some of this energy is also released as light, which is produced when electrons in the atoms of the reactants are excited and then return to their ground state, emitting photons of light in the process.

What factors can affect the intensity of light and heat produced in a chemical reaction?

The intensity of light and heat produced in a chemical reaction can be affected by several factors, including the amount of reactants present, the concentration of reactants, and the rate of the reaction. Other factors such as temperature, pressure, and the presence of catalysts can also play a role in determining the intensity of light and heat produced in a chemical reaction.

What are some practical applications of chemical reactions producing light and heat?

Chemical reactions producing light and heat have many practical applications in our daily lives. For example, combustion reactions are used to power vehicles and generate electricity. Bioluminescence is used in medical and biological research, as well as in the production of glow-in-the-dark products. Chemiluminescence is used in forensic science and in chemical analysis. These reactions also play a crucial role in many industries, such as in the production of plastics, fertilizers, and pharmaceuticals.

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