Because its components have changed into something entirely different, so you can't pick out what has gone in. For example, if you mix water and salt, you can not take the salt out of the water because it has reacted with it to be changed into somthing different.
This is a common misconception. Chemical changes can be reversed. It happens all the time, and there's a large branch of physical chemistry devoted to it. The problem stems from some teachers trying to oversimplify when teaching the difference between physical and chemical changes. A chemical change is one which produces a new substance, and a physical change is one which does not. Common examples of physical changes are melting and boiling water, and common examples of chemical changes are rusting and burning. Unfortunately, people extrapolate from these limited examples and their own limited knowledge, to say that since melting and boiling water is easy to reverse, and they don't know how to reverse rusting and burning, that 'chemical changes can't be reversed and physical ones can'. It just isn't true.
When we convert iron to steel, rusty scrap iron is often included in the mixture, and one of the reactions taking place in the converter vessel is the reduction of rust to iron. Burning isn't simple to reverse, not least because the products are usually carbon dioxide and water vapour which escape into the air. However, when plants photosynthesise they take carbon dioxide and water and convert them to glucose and oxygen, and eventually most fuels derive from that glucose. Additionally, not all physical changes are easy to reverse. If you freeze water you can easily turn it liquid again, true, but if you freeze liquid iron you have to heat it to 1538 degrees C to remelt it - hardly easy!
because they change the identity of the matter
a chemical change can't be normally reversed because in a chemical reaction, a new substance is formed with the help of the processes like heating, baking, electifying etc.
because,a chemical cant be seen be seen and the physical change can be reversed because is easier to be sen
chemical changes the substance where as physical breaks it down
The structure of molecules was changed.
Many chemical reactions are reversible.
The possibility for reversible chemical reactions exist.
This is not a rule !
Some chemical changes are reversible, others are not.
Chemical changes create new substances and cannot be reversed.Burning paperLighting a matchMixing sugar and waterPhysical changes do not create new substances and can be reversed.Crushing a canTearing paperChopping wood
Reversible changes are the chemical reactions that can be reversed, however most are non reversible. The ones that can be reversed is because the reaction can flow both ways.
Yes it is it's not reversible but physical changes are
It changes the chemical composition of the burned object making it kinda hard to reverse
Most cooking processes are chemical reactions. Generally, the reactions are non reversible and once cooked, food cannot be returned to an uncooked state. So, frying potatoes causes a non reversible chemical reaction. The question is not as precise as it might be. Changes can be physical or chemical. They can also be reversible or non reversible but it is important to note that many chemical changes are reversible just as many physical changes are reversible.
All physical changes are reversible.
chemical reactions are irreversible but physical changes are reversible
Some chemical changes are reversible, others are not.
some chemical changes can be reversed but they are hard to reverse usually
Chemical changes create new substances and cannot be reversed.Burning paperLighting a matchMixing sugar and waterPhysical changes do not create new substances and can be reversed.Crushing a canTearing paperChopping wood
the difference between a physical change and a chemical change is that a physical change is usually reversible whilst a chemical change is not reversible.
the difference between a physical change and a chemical change is that a physical change is usually reversible whilst a chemical change is not reversible.
I would argue that in theory all chemical changes are reversible. However it is certainly true that considerations of enthalpy and entropy mean that some are totally impractical to reverse.
Physical changes are reversible changes, such as change of state (boiling, melting etc), chemical changes are when something undergoes a reaction changing it's chemical makeup.
Physical changes and Chemical changes are both the same - this would be a reversible change.
Reversible changes are the chemical reactions that can be reversed, however most are non reversible. The ones that can be reversed is because the reaction can flow both ways.