Chemical or Physical Property? Chemical or Physical Change? Vocabulary: chemistry microscopic matter macroscopic physical property chemical property physical change chemical change evidence of chemical change solid liquid gas precipitate “Persistence of Memory” 1931 Salvador Dali

What is chemistry? The study of matter (anything that has mass and takes up space) and changes it undergoes.

Before we begin… Let’s distinguish between a property and a change. A quality or trait belonging to a substance. Static (unchanging.) Change: To make different in some way. Dynamic.

Physical Property Characteristic that can be observed without changing the identity of the substance. Examples: melting point boiling point color electrical conductivity density hardness shape malleability

Chemical Property Ability of a substance to undergo a change that transforms it into a different substance. Examples: flammability fermentability reactivity with acids rustability

Physical Change A change in a substance that does not involve a change in the identity of the substance.

Physical Change Examples Phase changes such as… freezing (liquid to solid) melting (solid to liquid) sublimating (solid to gas) boiling (liquid to gas)

Speaking of phase changes… What are the phases (or states) of matter? Gases Properties: flow easily (macroscopic) - particles can move/slide past one another (microscopic) takes the shape and volume of container (macroscopic) easily compressible (macroscopic) because there is a lot of space between particles (microscopic) As

Speaking of phase changes… What are the phases (or states) of matter? Liquids Properties: flow easily (macroscopic) - particles can move/slide past one another (microscopic) have a fixed volume but take shape of container (macroscopic) not easily compressible (macroscopic) because there is very little space between particles (microscopic)

Speaking of phase changes… What are the phases (or states) of matter? Solids Properties: rigid (macroscopic) - particles cannot move/slide past one another (microscopic) have a fixed volume and shape (macroscopic) not easily compressible (macroscopic) because there is very little space between particles (microscopic)

More Physical Change Examples cutting dissolving mixture separation

Chemical Change A change in which one or more substances are converted into different substances. (There is a new substance!!!!!!!)

How can you tell if a chemical change has occurred? Examine each of the following pictures and identify evidence of chemical change.

Chemical Change Examples

Chemical Change Evidences of a chemical change (i.e., the formation of a new substance): Color change Change in energy (hotter, colder, or light) Formation of a gas Formation of a precipitate

Precipitate What is a precipitate? A solid that comes out of solution in a chemical reaction.

Practice! Identify each of the following examples as a physical property, chemical property, physical change, or chemical change. Give evidence for your answer!

Practice! Melting candle wax Burning wood Dissolving salt in water physical change (no new substance formed; solid to liquid wax) Burning wood chemical change (new substance formed; color change, gas produced, heat produced) Dissolving salt in water physical change (no new substance formed; salt can be easily recovered, did not turn into something new)

Practice! Tearing a piece of paper An egg yolk is yellow physical change (no new substance formed; different form of same substance) An egg yolk is yellow physical property (characteristic of the substance; can be observed without changing the substance) Magnesium can react with acid chemical property (characteristic of the substance; must change the substance to observe the characteristic)

Practice! Baking bread chemical change (new substance formed; color change, gas produced) What type of change seems to be taking place in the picture below? physical change (objects are melting but not changing into new substances)