Matter: Changes and Properties

During a physical change, a substance changes some physical property, but it is still the same material with the same chemical composition. Ex. Water can change states to be solid, liquid, or gas gas H2O solid liquid

Any change involving a rearrangement of atoms. Chemical Change: Any change involving a rearrangement of atoms. http://www.pdsm.wpafb.af.mil/toprac/atoms_full_std.gif

Recognizing Chemical Changes Energy is absorbed or released (temperature changes hotter or colder, light released) Color changes Gas production (bubbling, fizzing, or odor change; smoke) Formation of a precipitate - a solid that separates from solution (won’t dissolve) Irreversibility - not easily reversed

The formation of a compound Chemical Change The formation of a compound Physical Change The formation of a mixture

Law of Conservation of Matter During a chemical change, matter is neither created nor destroyed. Conservation of Matter: Matter can neither be created nor destroyed. Atoms rearrange in chemical reactions – the macroscopic (what we see) view of things may appear as though ‘new’ matter has been created. However, at the microscopic level we would see only that compounds and molecules have been broken apart and rearranged into new compounds and molecules (from the same atoms we started with). This is a demonstration using potassium iodide mixed with lead nitrate to yield a precipitate of lead (II) iodide and soluble potassium nitrate. A small test tube filled with lead nitrate is resting inside the Erlenmeyer flask. When inverted, the chemical reaction occurs. No new material is added to the flask - it is a closed system. During the chemical reaction, atoms are rearranged. The product has different properties (i.e. it changes from colorless to yellow) than the reactants. Lead (II) iodide is very toxic. Dispose of waste in a responsible manner. Lead (II) iodide is also the pigment added to road stripe paint. Reactants yield Products

This is an image showing molecules of a compound This is an image showing molecules of a compound. Which of the pictures below represent a chemical change and which represent a physical change? Chemical Chemical Physical

Decide whether each is a chemical or physical change. Boil Burn Condense Corrode Crumple Ferment Melt Rust Crush Freeze Oxidize Tarnish Explode Grind Rot Vaporize

Decide whether each is a chemical or physical change. Boil- physical Burn- chemical Condense- physical Corrode-chemical Crumple- physical Ferment-chemical Melt- physical Rust- chemical Crush- physical Freeze- physical Oxidize- chemical Tarnish- chemical Explode- chemical Grind- physical Rot- chemical Vaporize- physical

Physical and Chemical Properties Examples of Physical Properties Boiling point Color Slipperiness Electrical conductivity Melting point Taste Odor Dissolves in water Shininess (luster) Softness Ductility (wire) Viscosity (resistance to flow) Volatility (evaporates) Hardness Malleability (sheet) Density (mass / volume ratio) Examples of Chemical Properties Burns in air Reacts with certain acids Decomposes when heated Explodes Reacts with certain metals Reacts with certain nonmetals Tarnishes Reacts with water Is toxic

INTENSIVE property - Does not change depending on the size of the sample color, melting point, boiling point, odor, density Ex. A cup of water will start to boil at the same temperature as a whole pot of water EXTENSIVE property - Does change depending on the size of the sample mass, volume, heat content (calories) Ex. A mini Snickers bar has less calories than a full size Snickers bar