Ch. 2 - Matter and Change 2.1 Properties of Matter 1

Recall… From ch. 1… Matter – anything with mass & volume (e.g., air; non-e.g., heat) Understanding matter begins with observing properties. 2

Describing Matter “Types” of properties: Extensive *or* Intensive depends upon amount (mass, volume) *or* Intensive depends upon type of matter (hardness, color, density) 3

Identifying Substances AND Physical Property observed without changing the composition *or* Chemical Property (pg. 53) observed when matter changes its composition; reactivity 4

Identifying Substances matter with uniform & definite composition; “pure” “Since a substance has identical composition, every sample has identical intensive properties.” 5

States of Matter Three states of matter Solid, liquid, gas 6

Indefinite shape Indefinite volume Indefinite shape Definite volume 7

States of Matter Solid Definite shape & definite volume; a solid is its own container Particles tightly packed; orderly Rigid; nearly incompressible Expand slightly when heated 8

States of Matter Liquid Indefinite shape, definite volume; takes on shape of container Particles close together; free to move Not rigid; Almost incompressible Expand slightly when heated 9

States of Matter Gas Indefinite shape and indefinite volume takes shape and volume of container Particles very far apart; mostly “empty space” Easily compressible 10

States of Matter Vapor o 27 C The gaseous state of a substance that normally exists as a solid or liquid. o 27 C 11

Physical Changes Reversible (Irreversible) Physical changes do not change the composition (identity) of matter. Reversible (Irreversible) The change can “undone” Able to retrieve original sample 12

Physical Changes Most physical changes involve a change in temperature. Increase temperature, particles move faster (more kinetic energy). 13

2.2 Classifying Mixtures Mixture – a physical blend of 2+ substances For example: Air = nitrogen + oxygen + carbon dioxide + argon A substance has fixed composition; the composition of a mixture varies. 14

Classifying Mixtures Phase – any distinct part within a mixture. Two types of mixtures: 1. Heterogeneous – a mixture that is not uniform in its composition; 2+ phases 2. Homogeneous – a mixture with uniform composition throughout; single phase 15

Separating Mixtures Physical properties can be used to separate mixtures. Filtration – separating a solid from a liquid in a heterogeneous mixture Distillation – separating the components of a liquid homogeneous mixture by their boiling points Chromatography – separating a mixture based on a differences in solubility 16

Distillation Filtration Chromotography 17

2.3 Elements & Compounds Substances are classified as element or compound. Element – simplest form of matter that has unique properties. Hydrogen = H carbon = C oxygen = O sodium = Na chlorine = Cl etc… 18

2.3 Elements & Compounds Compound – a substance composed of 2+ elements chemically combined in fixed proportion. Water = H2O table salt = NaCl carbon dioxide = CO2 sucrose = C12H22O11 Compounds can only be broken down into simpler substances by chemical means. There is no chemical process that will break elements down into simpler substances. 19

Properties of Compounds Compounds have different properties than the elements that make them up. SODIUM SODIUM + CHLORINE = CHLORIDE soft, silvery metal; yellow/green gas; white crystal; reacts w/ water; reacts with ammonia; seasoning & poisonous poisonous preserves food 20

Properties of Compounds Compounds have different properties than the elements that make them up. SODIUM SODIUM + CHLORINE = CHLORIDE soft, silvery metal; yellow/green gas; white crystal; reacts w/ water; reacts with ammonia; seasoning & poisonous poisonous preserves food 21

Water  Hydrogen + Oxygen Breaking Down Compounds Chemical Change – a change in the composition of matter; indicated as an arrow: Sugar  Carbon + Water Water  Hydrogen + Oxygen Chemical Change COMPOUND ELEMENT COMPOUND Chemical Change COMPOUND ELEMENT ELEMENT 22

ELECTROLYSIS OF WATER: H2O Hydrogen + Oxygen “to break” 23

Fig. 2.11 separated physically separated chemically 24

Symbols & Formulas Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds. For example: symbol: sodium = Na hydrogen = H chlorine = Cl oxygen = O formula: salt = NaCl water = H2O 25

2.4 Chemical Changes Chemical Property ability to undergo a chemical change; “reactivity”; “behavior” observed when matter changes its composition can be used to identify matter e.g., burn, rot, rust, decompose, ferment, explode, corrode, oxidize, etc… 26

2.4 Chemical Changes Chemical Change change in the composition of matter a.k.a. chemical reaction REACTANT(S)  PRODUCT(S) starting material finishing material; “new” substance 27

Recognizing Chemical Changes Possible “clues” to a chemical change: Transfer of energy (i.e. light &/or heat given off) Change in color Production of gas Formation of precipitate (a solid that forms out of a liquid) Clues do not necessarily confirm chemical change. 28

Conservation of Mass The Law of Conservation of Mass Mass is neither created nor destroyed in any chemical reaction. Mass of reactants = mass of products 29

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