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Physical & Chemical Properties & Changes
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Physical Property Physical property = a characteristic of matter that can be observed or measured without changing the identity of the substance Ex: mass volume density hardness color malleability ductility luster solubility viscosity melting, boiling, freezing points ability to conduct heat & electricity
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Malleability Malleability = capable of being shaped or formed (metals are malleable)
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Ductility Ductility = ability to be pulled or stretched into wires
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Luster Luster = “shiny” or reflects light
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Solubility Solubility = the ability to dissolve
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Viscosity Viscosity = “liquid thickness”
The thicker the liquid the slower it will pour
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Density Density = mass/volume D = m/V
Units for density include (but there are more!) g/mL or g/cm3 kg/L or kg/m3 Density can be used to identify unknown matter because density is a property of matter that doesn’t depend on size! Ex: Lead has a density of g/mL Therefore, all pure samples of lead will have a density of g/mL Ex: Copper has a density of 8.92 g/mL Therefore, all pure samples of copper will have a density of 8.92 g/mL
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Which is more dense liquid water or frozen (solid) water????
Density Density of H2O at 20 °C (68 °F)= g/mL (it’s ok if we round to 1.00 g/mL) Density of H2O at 0 °C (32 °F) = 0.92 g/mL Which is more dense liquid water or frozen (solid) water???? Liquid water! This is why ice floats…and fish don’t die in lakes in the winter!
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Density If an object is more dense than water it will generally sink in water If an object is less dense than water it will generally float in water Ex: If mercury (D = 13.6 g/mL), copper (D = 8.92 g/mL), and water at 20 °C (D = 1.00 g/mL) are combined what will be the order of the layers based on their densities?
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Density Water Copper Mercury
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Physical Property Physical properties can be described further as extensive or intensive. Extensive Property = property dependent of the amount of substance present or size SIZE MATTERS! Ex: mass, volume, length Intensive Property = property independent of the amount of substance present or size Ex: density, melting point, boiling point, freezing point, malleability, ductility, viscosity, all chemical properties SIZE DOESN’T MATTER!
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Intensive or Extensive?
Mass Color Density Shape Melting point Texture
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Physical Changes Physical changes = changes that alter matter but don’t change its chemical composition (make-up) Change appearance but not chemical make-up Ex: cut carrots shred paper chop wood grind coffee break glass melt candle wax boil water freeze alcohol dissolve NaCl in water
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Physical Change Action Words
Cutting Bending Grinding Crumple Split Crush Dissolve Melting Boiling (Vaporize) Freezing Sublime Condense Deposition Phase Changes
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Chemical Property Chemical property = the ability or inability of a substance to react
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Chemical Changes Chemical change = any change that causes one material to turn into a new material with a different chemical make-up Ex: Na+ reacting with Cl- road kill decomposing bananas rotting grapes fermenting iron rusting copper oxidizing cooking eggs grass growing
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Chemical Changes Chemical changes can also be called a chemical reactions. Chemical reactions can be represented by chemical equations. Reactants = starting substance(s) Products = new or end substance(s) Reactants and products separated by an arrow Reactants → Products
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Chemical Changes Law of Conservation of Mass = matter is neither created nor destroyed in ordinary chemical reactions, it’s simply rearranged. The mass (or amount) of the reactants and the products is equal. Ex: 2 NaN3 Na N2 150g 50g g Na2SO ZnBr2 ZnSO NaBr 100g g 130g g
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Chemical change action words
React Explode Decompose Rot Ferment Rust Oxidize Corrode Cook (with heat) Grow
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Chemical Change Signs of a chemical change or reaction
1. Temperature change Exothermic reaction = a reaction that gives off energy - warm/hot to touch Endothermic reaction = a reaction that absorbs energy - cool/cold to touch 2. Spontaneous change in color Ex: like when things rust, rot, burn 3. Gas produced 4. Odor given off 5. Formation of precipitate (solid)
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CHEMICAL OR PHYSICAL CHANGE?
Baking cookies Boiling water Dissolving salt Burning firewood Milk spoiling Metal rusting Tearing paper Melting ice
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