Matter – Properties and Changes Chapter 3

Organizing & Describing Matter Substances – matter that has a uniform and unchanging composition (pure substance) NaCl H2O Salt Water is not a pure substance – depending on where you take your sample it may have a different composition

Physical Properties of Matter A physical property is a characteristic that can be observed or measured without changing the sample’s composition Shape Taste Color Hardness Weight Melting Point Density Boiling Point Odor Pure substances will have uniform physical properties regardless of where the sample comes from – some (not all) of these properties can be used as identifying characteristics

Physical Properties of Matter Extensive Properties Properties dependent upon the amount of the substance present Length, volume & mass are dependent upon the sample observed Intensive Properties Properties that are independent of the amount of the substance present Density does not change – it is the same for all samples of a pure substance Can be used to identify samples of pure substances

Chemical Properties of Matter Chemical properties are based on the ability of a substance to combine with or change into one or more other substances May involve adding thermal or electrical energy May involve combining substances Example: iron forms rust when combined with air The inability of a substance to change is a chemical property Example: iron will not react with Nitrogen gas at room temperature

Observing Properties of Matter Properties may change depending on the conditions in which you observe the sample Physical & Chemical Properties depend on the temperature and pressure Water is liquid at room temperature, gas above 100 oC, and solid below 0oC When atmospheric pressure increases, the boiling point of water becomes higher (hotter) When atmospheric pressure decreases (as with increasing elevation) the boiling point becomes lower (cooler) We use the statement at standard temperature and pressure (o Kelvin and 1 atm)

States of Matter Solid – definite shape and volume Liquid – definite (or constant) volume & takes the shape of its container (no definite shape); flows Gas – flows to conform to the shape of its container; fills the entire volume of its container Solid Liquid Gas

Mixtures A mixture is a combination of two or more pure substances in which each pure substance maintains its individual chemical properties Anything mixed with water (ie salt water) is a mixture Aqueous solution

Types of Mixtures Homogeneous Heterogeneous Constant composition throughout Always has a single phase Salt water SOLUTIONS Heterogeneous Does not blend smoothly throughout Parts remain distinct Sand & water

Types of Solution Examples

Changes in Matter Physical Changes Changes that alter the substance without changing its composition Examples ∆ in State of matter (changes depend on temperature and pressure) Bend Tear Grind Crumple Split Crush Chemical Changes Process that involves one or more substances changing into new substances New substances are formed with new compositions and different properties than the reactants Starting substances are called reactants Ending substances are called products Examples – rust, explode, oxidize, corrode, tarnish, ferment, burn, rot

Indicators of Chemical Changes Formation of a gas (bubbles) Formation of a solid (precipitate) Generally, color changes Energy given off (heat, light, sound) Change in Odor

Massreactants = Massproducts Conservation of Mass Mass is neither created nor destroyed during a chemical reaction – it is conserved Massreactants = Massproducts

Elements Pure substances that cannot be separated into simpler substances by physical or chemical means 91 elements occur naturally on Earth Unique Chemical Name & Symbol (made of one, two or three letters & first letter is always capitalized Organized into the Periodic Table

Compounds Combination of two or more different elements that are combined chemically Water, table salt, sugar, aspirin Can be broken down into simpler substances by chemical means Typically involves energy

Law of Definite Proportions Elements that combine to form compounds in definite proportions Regardless of the amount, a compound is always composed of the same elements in the same proportion by mass Percent by mass = mass of the element x 100 mass of compound

Law of Multiple Proportions When different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers

Understanding Matter