It is important to understand the differences
between physical and chemical changes.
Some changes are obvious, but others can
seem tricky. It helps to think of physical changes
as those involving changes that don’t change
the make up of the substance, while chemical
changes are those that create a new
substance.
Physical Changes involve energy.
The energy changes the
substance, but the composition or
make up of the substance does
not change. For example, if you
step on a soda can, you use
energy to change the shape of
the can, but the can is still made
up of the same aluminum that it
was to start with.
Physical changes include changes in state of matter.
These are sometimes confusing, but remember – melted
ice is the same water that started as frozen water in the
ice cube. Steam given off when water is boiled is just
water in its gas form.
Signs of a physical change:
If it ONLY changes –
1. Size
2. Shape
3. State of matter
Chemical changes also involve
energy, but in a chemical
change, the result is a new
substance that is chemically
different from the original
substance. The molecules in a
chemical change experience a
change in structure. Chemical
bonds are broken and new
arrangements in the molecules
occur.
The substances produced in a chemical change has
properties that are different from the original
substance. Once a chemical change has occurred, it
cannot easily be changed back to the original
substance.
Signs of a possible chemical
change:
IF the substance Liquid
1.
2.
3.
4.
5.
6.
Produces a gas (bubbles)
Changes temperature
Changes color
Produces a precipitate (a
solid in a liquid)
Gives off light
Gives off a new odor
The most important thing to remember about chemical
changes is that they result in the formation of a new
substance.