Chemical and Physical Changes

Physical Property A physical property is an aspect of matter that can be observed or measured without changing it. Examples of physical properties include colour, state and volume.

Chemical Property A chemical property may only be observed by changing the chemical identity of a substance. This property measures the potential for a substance to undergo a chemical change. Examples of chemical properties include reactivity with acids and flammability.

Changes in Matter Changes in matter can be classified into three main categories: Physical, Chemical and Nuclear. To determine the type of change that has occurred, consider the following definitions.

Physical Change A physical change does NOT produce a new substance. Physical changes are concerned with energy and states of matter. 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.

Chemical Change A chemical change produces a new substance. Chemical changes take place on the molecular level. 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.

Nuclear Changes A nuclear change occurs at the atomic level. It involves changes in nuclear structure, such as fission (splitting) of a nucleus or an atom, or fusion (combining) of neutrons and protons to form heavier atoms. Read more: http://wiki.answers.com/Q/What_is_a_nuclea r_change#ixzz1bFUIqtuJ We won’t be focusing on this type of change.

How Can You Tell What Changes is Occurring? A chemical change makes a substance that wasn't there before (substance with new properties is formed) In a physical change, the starting and ending materials are the same, even though they may look different.

Examples of Changes Please watch the following demonstration and try to determine what type of change is being shown.

Clues a Chemical Changes Has Occurred There may be clues that a chemical reaction took place, such as: light or heat are produced colour change gas production formation of a solid precipitate odour

Look for an indication that a chemical change occurred. If you don't see any of these indications, a physical change likely occurred. In some cases, it may be hard to tell whether a chemical or physical change occurred. For example, when you dissolve sugar in water, a physical change occurs. The form of the sugar changes, but it remains the same chemically (sucrose molecules).

In a nutshell, a chemical change produces a new substance, while a physical change does not. A material may change shapes or forms while undergoing a physical change, but no chemical reactions occur and no new compounds are produced.