Introduction to Chemical Reactions Signs of chemical reactions, & properties.

Physical properties Characteristics of a material that are observed without changing the identity of the substance. Examples: color, density, conductivity, malleability (how easy it is to reshape), melting point, boiling point, & solubility (whether a substance will dissolve in another substance).

Physical change A change that results in a difference in the material, but does not change the type of material. The composition of the material is the same after the change as it was before. The material still has the same chemical and physical properties as before. Examples: tearing paper, crumpling paper, coloring on paper, breaking glass, dissolving salt in water, getting paper wet

Chemical properties Characteristics of a material that describe how the material acts in the presence of other types of material. Examples: non-reactive with plastic. Flammable at high temperatures Reacts with acid to produce a gas Does not react with air

Signs of a chemical reaction Chemical rxns occur all around us everyday. A chemical reaction is typically includes at least one of the following signs: Absorption or release of energy, such as light or heat, w/o outside influence. Formation of a gas in the absence of heating. djamdance.googlepages.com www.glasgowsciencecentre.org

Signs cont’d Color change that is not the result of color blending. Formation of a precipitate (a solid that does not dissolve in the liquid). Change in odor.

Chemical changes A change that results in the production of new materials with new properties. The materials after the change are different than the materials present before the change. These new materials have different chemical & physical properties.