Chemical Properties

Learning Goals Identify Chemical Properties Identify physical and chemical changes

Chemical Property The ability of a substance to change (react) and form new substances

Combustibility This property describes how easily a substance can catch on fire. Example:

Two trees, different combustibilities

Light Sensitivity Some substances are very sensitive to light and actually change into a different substance when exposed to light. Example: hydrogen peroxide (used as a disinfectant) is sensitive to light and sold in dark brown bottles.

Stability The ability of a substance to remain unchanged The more stable a substance is, the longer it will take to break down Between water and hydrogen peroxide, which is more stable?

Toxicity The ability of a substance to cause harmful effects in plants and animals Example: DDT, Carbon monoxide

Physical and Chemical Change

Remember this question?

PHYSICAL CHANGES Physical changes involve a change in state. Gas Solid Liquid

In a physical change, the substance DOES NOT become a new substance. Physical changes can always be reversed

Examples: Dissolving sugar in water Melting Ice

Chemical Changes A chemical change results to a new substance being created. Chemical changes are very difficult to reverse.

Examples Lighting a match Baking a cake Heartburn medication

Example: Combustion Combustion occurs when heat is applied to a chemical.

Example: Rusting Rusting occurs when metals such as iron react with the oxygen gas in the air to form rust.

If you make two or more of the following observations then a chemical change has probably taken place:

The starting material is used up Heat is produced (feels warm) or absorbed (feels cold) The colour changes Gas bubbles form in a liquid Grains of solid precipitate form in the liquid

Class work Read pages 160 to 164 Do page 165 # 1, 2, 3, 5 Worksheets Physical and Chemical Properties Physical and Chemical Changes