Physical vs ChemicalChanges and Properties

Properties – what are they?

Property

• The arrangement of atoms determines the properties of the substance • Shape• Color• Texture• Odor• Luster• Transparency• Density• Size• Volume• Mass• Melting Point• Boiling Point

• Mass• Melting Point• Boiling Point• Freezing Point• Hardness• Resistance• Flamable• Conductivity• Magnetism• Insulator

• Will every substance have all these properties?

• Is the lack of a

property a property?

Physical Properties

Physical Properties

• Observations made about a substance that doesn’t change the substance itself

• You can stretch a rubber band, bend a piece of wire, or break a piece of gum.

• Because you are still left with the same substance when you are done, it is a physical property.

Physical Properties

• Appearance:• How would you describe a tennis ball?

(shape, color, state of matter)• How would you describe a soft drink?

(color, state of matter, taste)• You could also measure its volume and

temperature—these are all physical properties

Physical Properties

• Behavior:• Some physical properties describe the

behavior of a substance• For instance, objects containing iron (I.e.

safety pins) are attracted by a magnet• Think about a soft drink. If you were to knock

it over, it would spread onto the table and floor—the ability to flow is a physical property of liquids

Physical Changes

Physical Change

• A physical changephysical change is a change in which a substance changes its physical properties without changing its chemical identity.

• These changes might involve energy changes, but the kind of substance—the identity of the element or compound—does not change!

Physical Change

• Heat Curve

Physical Change

Physical Changes

• KEYWORDS:– Freezing– Melting– Boiling– Condensing– Vaporizing– Evaporating– Change in size or shape– Dissolving

Chemical Properties

Chemical Properties

• The chemical characteristics of a substance that tend to change the chemical identity.

• A chemical property of Fe (Iron) is rusting.

• Limestone and acid gives off gas in the form of bubbles –good indication that there is a chemical change occurring.

Chemical Changes

Chemical Change

• The change of a substance into other substances through a reorganization of atoms.

• Chemical reactions involve chemical changes.

Chemical Changes

• KEYWORD:– New substance formed?– Burning– Change in color– Gas given off (bubbles)– Precipitate (solid that falls out of solution)– Change in odor– Rusting

Chemical Reactions

Chemical Reactions

• Bonds between atoms are formed or broken causing substances to combine and recombine as different molecules.

• Represented by chemical equations• Metabolism – all of the chemical rxns that

occur within an organism

Chemical Reactions

2H2 + O2 2 H2O

Reactants Products

YIELDS

• Atoms are neither created nor destroyed in a chemical reaction, just rearranged!

• The Chemical Equation must be balanced!!

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