Chemical vs. Physical Changes p. 5-7 notes

Physical Change the substances are not altered chemically, but are merely changed to another phase (i.e. gas, liquid, solid) or separated or combined. No change occurs in the identity of the substance

Chemical change the substances are altered chemically and display different physical and chemical properties after the change. Atoms in the reactants are rearranged to form one or more different substances Old bonds are broken; new bonds form

Indicators/Signs of a Chemical Change (these are not fool proof) Chemists Get Practice Trying Labs Color change Gas/bubbles Precipitate, ppt (a solid forms) Temperature change Exothermic (hot) or endothermic (cold) Light given off Typically, more than one indicator will be seen.

Learning Check Classify each of the following as a 1) physical change or 2) chemical change A. ____ a burning candle B. ____ melting ice C. ____ toasting a marshmallow D. ____ cutting a pizza E. ____ Tarnished silver

Solution Classify each of the following as a 1) physical change or 2) chemical change A. __2__ a burning candle B. __1_ melting ice C. __2__ toasting a marshmallow D. __1__ cutting a pizza E. __2__ tarnished silver

Chemical Reaction A process in which at least one new substance is produced as a result of chemical change.

In a chemical reaction The way atoms are joined is changed Atoms aren’t created or destroyed. Can be described several ways: In a sentence Copper reacts with chlorine to form copper (II) chloride. In a word equation Copper + chlorine ® copper (II) chloride Formulas Cu+ Cl2  CuCl2

A Chemical Equation Reactants Products

Conservation of Mass and Energy Mass and Energy cannot be created or destroyed, but can change form

Symbols used in equations  separates the reactants from products Read as “reacts to form” or “yields” + read as “and” or “reacts with” (s) after the formula -solid (g) after the formula -gas (l) after the formula –liquid (aq) after the formula- aqueous solution Dissolved in water.

More Symbols used in Equations ­ used after a product indicates a gas; same as (g) ¯ used after a product indicates a solid or ppt (precipitate); same as (s)

Even More Symbols used in Equations indicates a reversible reaction (More later) shows that heat is supplied to the reaction is used to indicate a catalyst used supplied, in this case, platinum.

What is a catalyst? A substance that speeds up a reaction without being changed by the reaction. Enzymes are biological or protein catalysts.

Diatomic elements There are 8 elements that never want to be alone. If they are not with another element, they form diatomic molecules. H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 , and At2 Brother HON CLIF 1 + 7 pattern on the periodic table

Sulfur, when alone, exists as S8 Phosphorus, when alone, exists as P4 Sulfur & Phosphorus Sulfur, when alone, exists as S8 Phosphorus, when alone, exists as P4