Physical & Chemical Properties & Changes

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

Malleability Malleability = capable of being shaped or formed (metals are malleable)

Ductility Ductility = ability to be pulled or stretched into wires

Luster Luster = “shiny” or reflects light

Solubility Solubility = the ability to dissolve

Viscosity Viscosity = “liquid thickness” The thicker the liquid the slower it will pour

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 11.35 g/mL Therefore, all pure samples of lead will have a density of 11.35 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

Which is more dense liquid water or frozen (solid) water???? Density Density of H2O at 20 °C (68 °F)= 0.998 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!

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?

Density Water Copper Mercury

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!

Intensive or Extensive? Mass Color Density Shape Melting point Texture

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

Physical Change Action Words Cutting Bending Grinding Crumple Split Crush Dissolve Melting Boiling (Vaporize) Freezing Sublime Condense Deposition Phase Changes

Chemical Property Chemical property = the ability or inability of a substance to react

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

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

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  2 Na + 3 N2 150g 50g 100g Na2SO4 + ZnBr2  ZnSO4 + 2 NaBr 100g 200g 130g 170g

Chemical change action words React Explode Decompose Rot Ferment Rust Oxidize Corrode Cook (with heat) Grow

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)

CHEMICAL OR PHYSICAL CHANGE? Baking cookies Boiling water Dissolving salt Burning firewood Milk spoiling Metal rusting Tearing paper Melting ice