When we say "sunlight fades colors" and "sunlight bleaches", does it carry similar similar meaning? 

How about "discolor". Is it only a different term for the same idea?

There are different but contradictory results on Google. Is sun bleaching of clothes or other objects are physical or chemical change?

I believe that it should be chemical change, because it is that the sun breaks the bonds and changes color of things.

I'm not able to find out a general equation for such reaction. Is there any such equation?

When the color of an object is faded or bleached, is there any end products during the reaction which would go away from the object?

Is there any reliable sources of reading on web about such topic that you can recommend?

I think a good search engine keyword would be "organic and inorganic dyes and decomposition under sunlight", "organic and inorganic dyes and degradation under sunlight", or "photocatalytic degradation of dyes". I immediately received several articles.

Edited July 12, 20232 yr by Sensei

2 hours ago, kenny1999 said:

When we say "sunlight fades colors" and "sunlight bleaches", does it carry similar similar meaning? 

How about "discolor". Is it only a different term for the same idea?

There are different but contradictory results on Google. Is sun bleaching of clothes or other objects are physical or chemical change?

I believe that it should be chemical change, because it is that the sun breaks the bonds and changes color of things.

I'm not able to find out a general equation for such reaction. Is there any such equation?

When the color of an object is faded or bleached, is there any end products during the reaction which would go away from the object?

Is there any reliable sources of reading on web about such topic that you can recommend?

You are quite right about this being a chemical process- photochemical, more specifically. Absorption of light by dyes creates excited states with antibonding character and/or unpaired electrons. These are reactive and may form new bonds, either within the molecule or between molecules. If this happens, then more often than not it will interrupt the conjugated bonding systems responsible for absorption in the visible, hence causing a bleaching or fading effect. But there won't be any one reaction scheme for this. There is an article here about chromophores that explains the type of bonding responsible: https://en.wikipedia.org/wiki/Chromophore.  Interrupting the chain of alternating single and double bonds will change the wavelength at which the molecules absorbs light, generally towards the UV.

Edited July 12, 20232 yr by exchemist

There is a previous thread on the subject that contributes with answers. :

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