What’s the MATTER:Classify Changes of Matter Chemical vs. Physical Changes
Matter, Classify Changes of Matter At the conclusion of our time together, you should be able to: Characterize various changes of matter Recognize that a change of state in matter is a physical change
Physical Change Physical • A change in matter from one form to another without changing its chemical properties • the substances are not altered chemically, but are merely changed to another phase (i.e. gas, liquid, solid) or separated or combined. • (most can be reversed) • No change in identity of the matter.
Physical Change • Examples = • Change in state or phase change • Dissolving • Compressing • Light emission/absorption • Electrons passing through metals
Physical Change More Examples = • boiling of a liquid • melting of a solid • dissolving a solid in a liquid to give a homogeneous mixture • making a solution
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 differentsubstances • Old bonds are broken; new bonds form
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2 1 Chemical Change Chemical • Bonds are made / broken • Change in oxidation states Li +1 Cl-1 Cl-1
Possible Signs of a Chemical Change“Chemists Get Practice Trying Labs” • Color Change • Gas Produced ( not from boiling!) • Precipitate – a solid formed by mixing two liquids together • Temperature Change Exothermic (hot) or endothermic (cold) • Light 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 2 1 2 1 2
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
Examples of Chemical Change • Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules. • Burning hydrogen (H2) in oxygen (O2) gives H2O.
A Chemical Equation Reactants Products
Remember the Law of Conservation of Mass • In a physical change or a chemical reaction, mass (and energy) is neither created or destroyed, but can change form. (Antoine Lavoisier)
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.
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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
Matter, Classify Changes of Matter Let’s see if you can: Characterize various changes of matter Recognize that a change of state in matter is a physical change
Physical vs. Chemical Change • physical • chemical • physical • physical • chemical • Examples: • melting • flame produced • paper cut • dissolving salt in water • tarnishes in air
Physical vs. Chemical Change • chemical • physical • chemical • physical • physical • Examples: • rusting iron • mixing mud and water • burning a log • freezing water • grinding spices
A difference between physical change and chemical change is that • chemical change involves energy while physical change does not. • physical change involves energy while chemical change does not. • different kinds of molecules are present after a physical change but not after a chemical change. • different kinds of molecules are present after a chemical change but not after a physical change
In making a pizza, which process involves a chemical change? Mixing spices for the sauce Slicing pepperoni for the topping Spreading cheese on the pizza Baking the dough to form the crust
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