What is a chemical change?

1 Answer
Jun 9, 2016

I have said this before, but chemical change is characterized by the formation of new substances, and the making and breaking of chemical bonds.


So any process where this occurs is a chemical change by definition.

If we look at an example of physical change, a change of state:

#H_2O(s) rarrH_2O(g) rarr H_2O(g)#

We can see that although there has been a change in state, the #O-H# bonds of the water molecule remain unbroken, and that, therefore, this process characterizes PHYSICAL change.

On the other hand, the reaction of an alkali metal with water is unquestionably a chemical change:

#Na(s) + H_2O(l) rarr NaOH(aq) + 1/2H_2(g)uarr#

Strong bonds have been broken, and new chemical substances have been formed.