chapter 3 matter – properties and changes. organizing & describing matter substances –...
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CHAPTER 3
Matter – Properties and Changes
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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
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Physical Properties of Matter
A physical property is a characteristic that can be observed or measured without changing the sample’s composition
Shape TasteColor HardnessWeight Melting PointDensity Boiling PointOdor
• 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
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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
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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
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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)
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States of Matter
Solid – definite shape and volumeLiquid – 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
SolidGas
Liquid
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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
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Types of Mixtures
Homogeneous Constant composition throughout Always has a single phase Salt water SOLUTIONS
Heterogeneous Does not blend smoothly throughout Parts remain distinct Sand & water
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Types of Solution Examples
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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
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Indicators of Chemical Changes
Formation of a gas (bubbles)Formation of a solid (precipitate)
Generally, color changesEnergy given off (heat, light, sound)
Change in Odor
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Conservation of Mass
Mass is neither created nor destroyed during a chemical reaction – it is conserved
Massreactants = Massproducts
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Elements
Pure substances that cannot be separated into simpler substances by physical or chemical means
91 elements occur naturally on EarthUnique Chemical Name & Symbol
(made of one, two or three letters & first letter is always capitalized
Organized into the Periodic Table
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Compounds
Combination of two or more different elements that are combined chemically
Water, table salt, sugar, aspirinCan be broken down into simpler substances by chemical meansTypically involves energy
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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
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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
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Understanding Matter