What is the difference between chemical reactions and physical reactions,and chemical properties and physical properties

[Sigmarus]

Hi!So my exams are coming up and i got a few questions about what makes a chemical reaction,a physical reaction and the differences between chemical and physical properties.Thanks in advance!

[DrP]

A chemical reaction is one where the reactants actually change chemically. Like, acids and alkalis mixed react chemically to give salts and water.

 

A physical reaction (iirc) is something like the reaction you get with oil and water - there is no chemical reaction, but they separate and force each other apart physically. This physical attraction or repulsion between substances is physical because no chemical change takes place, although, the reaction is due to the chemistry of the molecules involved.

 

There is more to it - you could write an essay about it.

[Itoero]

An explanation I found on google:

"1. A physical change is reversible, a chemical change is not. For example, the freezing of water would be a physical change because it can be reversed, whereas the burning of wood is a chemical change - you can't 'unburn' it

 

2. A physical change is a change in which no new substance is formed; a chemical change results in the formation of one or more new substances. Again, consider the previous examples: Freezing water into ice just results in water molecules which are 'stuck' together - it's still H2O. Whereas burning wood results in ash, carbon dioxide, etc, all new substances which weren't there when you started."

 

=>You might say that physical/chemical reactions happen at the same time. You just call it chemical of physical depending on the used measuring devices.

 

[Sriman Dutta]

Example of a chemical change and a physical one will help a lot.

The combustion or burning of a fuel is a chemical change. Like, burning of methane is:

[math]CH_4 + 2 O_2 ---> CO_2 + 2 H_2 O [/math]

On the other hand the melting of ice to water is a physical change.

Clearly, a chemical change involves alterations in molecular structure but physical changes don't.

Edited April 26, 2017 by Sriman Dutta