Matter and Change Chapter 2

Properties of Matter Matter has many different properties These properties can be used to classify and identify various forms of matter Properties used to describe matter can be classified as extensive or intensive

Extensive & Intensive Properties Extensive properties Depend on amount of matter present Examples: ? Intensive properties Depend on type of matter Do not depend on amount of matter present Examples: ?

Identifying Substances A substance is matter that has a uniform and definite composition Any given substance will have a unique set of intensive properties These properties can be used to identify or separate the substance from other substances. Problem: How could you separate a mixture of iron filings from sugar?

Physical Properties Can be observed or measured without changing the identity of the substance

States of Matter: Solids Solids Definite shape Definite volume Particles fixed in place

States of Matter: Liquids Liquids Definite volume Indefinite Shape Particles can move past each other

States of Matter: Gases Gases Indefinite shape Indefinite volume Easily compressed Particles very far apart Particles moving rapidly

Vapors and Gases Gases are substances that are normally in a gaseous state at room temperature Examples: O 2, N 2, He Vapors are substances in a gaseous state that are normally solid or liquid at room temperature H 2 O ( l ) + heat  H 2 O ( g )

Physical Changes Changes to a substance that do not involve a change in composition Reversible or irreversible Melting Freezing Stretching Chopping Grinding

2.2 Mixtures A physical blend of two or more substances Types of mixtures Homogeneous Composition is uniform Consists of a single phase Heterogeneous Composition is not uniform throughout Have two or more phases

Phases of a Mixture Some heterogeneous mixtures have homogeneous regions called phases

Separating Mixtures Use different physical properties of substances to separate components Some techniques include…. Filtration Chromatography Many types Distillation

Liquids can be separated by boiling point

2.3 Elements & Compounds An element is the simplest form of matter that has a unique set of properties.  Contains only one type of atom  C, H, O, He, Ag, Na, K, etc.  Periodic Table contains all known elements

Elements & Compounds A compound is a substance that contains two or more elements chemically bonded in a fixed proportion.  Contains two or more different types of atoms  H 2 Owater  C 6 H 6 benzene  Ca(OH) 2 calcium hydroxide  C 2 H 4 O 2 acetic acid

Elements are the simplest form of matter Elements cannot be broken down into simpler substances Compounds can C 6 H 12 O 6 → __ C + __ H 2 O C 6 H 12 O 6 → 6 C + 6 H 2 O

Properties of Compounds Usually quite different than the properties of the elements making up the compound Different compounds have different physical and chemical properties

Stop and think……. In chemistry, what is a particle? Is a compound a mixture? Why or why not?

2.3 Classifying Matter

Symbols & Formulas Elements are represented by symbols Compounds are represented by formulas Interpreting chemical formulas Subscripts indicate the number of atoms HNO 3 Na 2 O C 12 H 22 O 11

Compounds have a constant chemical composition

2.4 Chemical Reactions Chemical property Tendency to undergo a specific type of chemical change E.g. acids donate protons HCl + NaOH → NaCl + H 2 O Chemical changes Involve a change in chemical composition Atoms are rearranged to form new substances HCl + NaOH → NaCl + H 2 O

Chemical Reactions Common terms that suggest chemical change Rot, ferment, corrode, rust, burn, decompose, etc. Process of chemical change Reactants → Products HCl + NaOH → NaCl + H 2 O Fe + S → FeS C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 O

Recognizing Chemical Change: Evidence? Energy transfer Color change Formation of a gas HCl + NaHCO 3 → NaCl + H 2 O + CO 2 (g) Formation of a precipitate An insoluble solid product CaCl 2 (aq) + NaOH (aq) → Ca(OH) 2 (s) + NaCl (aq)

Law of Conservation of Mass During chemical reactions matter is neither created or destroyed Mass of reactants = mass of productions 50 g + 25 g → 65 g + 10 g Beginning mass = ending mass