Chemical Properties and Change Chemical Change Elements versus Compounds Chemical Symbols Chemical Reactions Law of Conservation of Mass

 Breaking Down Compounds A chemical change is a change that produces matter with a different composition than the original matter. When table sugar is heated, it goes through a series of chemical changes.

The final products of these chemical changes are solid carbon and water vapor. The following diagram summarizes the process.

 Properties of Compounds In general, the properties of compounds are quite different from those of their component elements. When the elements sodium and chlorine combine chemically to form sodium chloride, there is a change in composition and a change in properties.

Sodium reacts violently with water. Sodium vapor produces the light in some street lamps. Chlorine is deadly to life. It is used in pools to kill harmful bacteria.

Sodium Chloride (commonly known as table salt) is used to season or preserve food. It does not react with water and is essential for life.

Question 1

Each element is represented by a one or two-letter chemical symbol.

 2.Passing an electric current through a certain substance produces oxygen and sulfur. This substance cannot be a(n)‏ compound. mixture. element. solution.

 3.Which of the following is a mixture? sodium chloride carbon dioxide sucrose air

 4.The symbol for the element potassium is K. Po. P. Pt.

Chemical Changes During a chemical change, the composition of matter always changes. The ability of a substance to undergo a specific chemical change is called a chemical property. Chemical properties can be used to identify a substance. But chemical properties can be observed only when a substance undergoes a chemical change.

A magnet separates iron from sulfur. This is an example of a physical change. A mixture of iron and sulfur is heated. The iron and sulfur react and form iron sulfide. This is an example of a chemical change.

 A chemical change is also called a chemical reaction.  One or more substances change into one or more new substances during a chemical reaction.  A substance present at the start of the reaction is a reactant.  A substance produced in the reaction is a product.

 Possible clues to chemical change include: a transfer of energy a change in color the production of a gas the formation of a precipitate.

A precipitate is a solid that forms and settles out of a liquid mixture. Clues to chemical changes have practical applications.

The law of conservation of mass states that in any physical change or chemical reaction, mass is conserved. The conservation of mass is easily observed when a change occurs in a closed container.

Types of Mixtures Suspension – a mixture where particles settle out if left undisturbed Colloid – A heterogeneous mixture is tiny particles what never settle out.  Tyndall Effect – The scattering of light caused by colloids  Soluble: can dissolveInsoluble: Cannot  Miscible : two liquids that are soluble in each other.  Immiscible : two liquids that can be mixed, but separate shortly afterwards.

Crystallization The separation technique that results in the formation of pure solid particles of a substance from the dissolved substance.

Chromatography A technique that separates the components of a mixtures based on the ability of each component to travel or be drawn across the surface of another material.

Phase Changes Solid to Liquid  Melting Liquid to Gas  Boiling/Evaporate Gas to Liquid  Condensation Liquid to Solid  Freezing Solid to Gas  Sublimation Gas to Solid  Deposition

 5.Which of the following is a chemical reaction? melting of lead dissolving sugar in water rusting of iron crushing of stone

 6.Which of the following is NOT a possible clue that a chemical change is taking place? a change of state a change in color production of a gas formation of a precipitate

 7.During any chemical change, the mass of the products is always equal to the mass of the reactants. always greater than the mass of the reactants. always less than the mass of the reactants. sometimes different than the mass of the reactants.