Chemical and Physical Changes

Chemical & Physical Changes

            It is important to understand the difference between chemical and physical changes. The two types are based on studying chemical reactions and states of matter. 

·         Chemical Changes

               Chemical changes take place on the molecular level. A chemical change produces a new substance. Examples of chemical changes include combustion (burning), cooking an egg, rusting of an iron pan, and mixing hydrochloric acid and sodium hydroxide to make salt and water.

·         Examples of Chemical Changes

1)      burning wood

2)      dissolving salt in water

3)      mixing acid and base

4)      digesting food

·         Physical Changes

              Physical changes are concerned with energy and states of matter. A physical change does not produce a new substance. Changes in state or phase (melting, freezing, vaporization, condensation, sublimation) are physical changes. Examples of physical changes include crushing a can, melting an ice cube, and breaking a bottle.

·         Examples of Physical Changes

1)      crumpling a sheet of paper

2)      melting an ice cube

3)      casting silver in a mold

4)      breaking a bottle

·         How to Tell Chemical & Physical Changes Apart

              A chemical change makes a substance that wasn't there before. There may be clues that a chemical reaction took place, such as light, heat, color change, gas production, odor, or sound. The starting and ending materials of a physical change are the same, even though they may look different.