# What is a chemical change?

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.

#### Explanation:

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:

${H}_{2} O \left(s\right) \rightarrow {H}_{2} O \left(g\right) \rightarrow {H}_{2} O \left(g\right)$

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:

$N a \left(s\right) + {H}_{2} O \left(l\right) \rightarrow N a O H \left(a q\right) + \frac{1}{2} {H}_{2} \left(g\right) \uparrow$

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