Chemistry Chapter 2: Matter and Change

2.1 Properties of Matter Properties used to describe matter can be extensive or intensive: Extensive – Depends on the amount of matter in a sample. Examples: mass and volume Intensive – Depends on the type of matter in a sample, not the amount of matter. Examples: Hardness or texture.

Identifying Substances Substance – matter that has a uniform and definite composition Every sample of a given substance has identical intensive properties because every sample will have same composition Physical property – quality or condition of a substance that can be observed or measured without changing the substance’s composition

Identifying Substances Physical properties can be used to identify substances. Table 2.1 on page 40: What is a solid (at room temperature) yellow substance that melts at 115oC and boils at 445oC?

States of Matter Solid Liquid Gas Definite shape and volume, almost incompressible Liquid Indefinite shape, flows, definite volume, almost incompressible, expand slightly when heated Gas takes shape and volume of container. Vapor term used to describe gaseous state of substance that is generally a liquid or solid at room temp (water vapor)

Physical Changes During physical change, some properties of a material change, but the composition does not. Examples: Melting, freezing, boiling, condensing. Can be reversible (melting or boiling) or irreversible (cutting hair, cracking an egg)

2.2 Mixtures Mixture – physical blend of two or more components Heterogeneous – composition not uniform throughout chicken noodle soup, pizza Homogeneous – composition is uniform. Another name is solution. Many are liquids, some gases (air) and some solids (steel – mixture of iron, chromium, and nickel)

Separating Mixtures Differences in physical properties can be used to separate mixtures Olive oil and vinegar – could decant, or freeze until oil turns to solid Filtration – separate solid from liquid Distillation – liquid boiled to produce vapor which is condensed back to liquid

2.3 Elements and Compounds Element – simplest form of matter that has a unique set of properties Compound – substance that contains two or more elements in a fixed proportion C3H8 is propane and CH4 is methane Compounds can be broken down into simpler substances by chemical means, but elements cannot.

Breaking Down Compounds Need chemical changes – produces matter with a different composition than original matter. Heating sugar is example heat Sugar carbon(s) + water(g)

Properties of Compounds Generally, properties of compounds are different than those of their component elements. Water is an example: H and O are gases at room temp while H2O is a liquid

Distinguishing Substances and Mixtures Variable composition Definite composition

NaCl C6H12O6 Symbols and Formulas Chemists use symbols and formulas to represent elements and compounds First letter of chemical symbol always capitalized. When second letter is used, it is lowercase. NaCl C6H12O6

2.4 Chemical Reactions Reactant – substance present at start of reaction Product – substance produced in a reaction Clues to a chemical change: transfer of energy, change in color, production of a gas, formation of a precipitate.

Conservation of Mass During any chemical reaction, the mass of the products is always equal to the mass of the reactants. Law of Conservation of Mass – in any physical change or chemical reaction, mass is conserved.

Chapter 2 Problems 2, 5, 8, 11, 13, 14, 20, 21, 24, 25, 26, 27, 29, 30, 32, 34, 35, 40, 42, 43, 46, 49, 50, 54, 56, 60, 61, 62, 63, 66, 67, 69, 72, 76, 77, 80