Chapter 3Chapter 3

Section 3.2: Changes in Section 3.2: Changes in MatterMatter

ObjectivesObjectives Define physical change and list Define physical change and list

several common physical changes.several common physical changes. Define chemical change and list Define chemical change and list

several indications that a chemical several indications that a chemical change has taken place.change has taken place.

Apply the law of conservation of Apply the law of conservation of mass to chemical reactions.mass to chemical reactions.

Physical ChangesPhysical Changes A A physical changephysical change is a change that is a change that

alters a substance alters a substance without changing without changing its compositionits composition..

Cutting your hair or crumpling a Cutting your hair or crumpling a sheet of paper are examples of sheet of paper are examples of physical changes.physical changes.

Verbs describing a physical change Verbs describing a physical change include: TEAR, BREAK, BEND, SPLIT, include: TEAR, BREAK, BEND, SPLIT, CRUSH, BOIL, FREEZE, MELT. CRUSH, BOIL, FREEZE, MELT.

Note: Changes in state and ability to Note: Changes in state and ability to dissolve dissolve areare physical changesphysical changes..

Chemical ChangesChemical Changes A A chemical changechemical change is the change of one is the change of one

substance into a new, different substance.substance into a new, different substance. A chemical change is more commonly A chemical change is more commonly

referred to as a referred to as a chemical reactionchemical reaction.. Examples of chemicalExamples of chemical changes are thechanges are the fermentation of grapes,fermentation of grapes, the rusting of iron, the rusting of iron, and the changing color and the changing color of leaves in the fall.of leaves in the fall. Verbs describing a Verbs describing a chemical reaction would include…?chemical reaction would include…?

A Closer LookA Closer Look Iron reacts with oxygen in the air to form a Iron reacts with oxygen in the air to form a

new, different substancenew, different substance – rust. Rust is – rust. Rust is really a compound called iron oxide.really a compound called iron oxide.

Iron & rust have different compositions and Iron & rust have different compositions and different physical & chemical properties.different physical & chemical properties.

In the reaction, iron andIn the reaction, iron and oxygen, the starting oxygen, the starting substances, are called substances, are called the the reactantsreactants. The new. The new substances produced are substances produced are called the called the productsproducts..

Evidence of a Chemical Evidence of a Chemical ReactionReaction

A color change – The formation of rust is an A color change – The formation of rust is an excellent example of this.excellent example of this.

Production of a gas – Bubbles or a change in Production of a gas – Bubbles or a change in odor indicate a gas was produced.odor indicate a gas was produced.

Formation of a precipitate – Formation of a precipitate – An example of the productionAn example of the production of a solid in a liquid is seen in of a solid in a liquid is seen in the photo to the right.the photo to the right. An energy change – A changeAn energy change – A change in temperature indicates thatin temperature indicates that energy was absorbed or energy was absorbed or released. released.

Law of Conservation of MassLaw of Conservation of Mass Following the invention ofFollowing the invention of the analytical balance,the analytical balance, scientists, like Antoinescientists, like Antoine Lavoisier, observed manyLavoisier, observed many chemical reactions andchemical reactions and always found that thealways found that the mass before and after amass before and after a reaction did not change.reaction did not change.

Law of Conservation of MassLaw of Conservation of Mass

They summarized this phenomenon They summarized this phenomenon in a in a law: law: mass is neither created or mass is neither created or destroyed during a chemical reaction destroyed during a chemical reaction – it is conserved.– it is conserved.

MassMassreactantsreactants = Mass = Massproductsproducts

Practice ProblemsPractice Problems 10.00 g of mercury (II) oxide is heated until 10.00 g of mercury (II) oxide is heated until

it is converted to liquid mercury and it is converted to liquid mercury and oxygen gas. If the mercury has a mass of oxygen gas. If the mercury has a mass of 9.26 g, what is the mass of the oxygen 9.26 g, what is the mass of the oxygen formed?formed?

10.3 g of Al are allowed to react with 100.0 10.3 g of Al are allowed to react with 100.0 g of Br. After the reaction, no Al remains g of Br. After the reaction, no Al remains but 8.5 g of Br remains unreacted. How but 8.5 g of Br remains unreacted. How many grams of the compound aluminum many grams of the compound aluminum bromide were formed?bromide were formed?