Properties of Matter Physical vs Chemical Chapter 21.4 & 21.5 P

Physical properties Physical properties are observations that you make without changing the identity of the substances that make up the material For instance, you can stretch a rubber band or bend a piece of wire The ability to stretch or bend are physical properties Some other physical properties are color, shape, size, melting point, and boiling point

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 Remember that 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 Change If you break a piece of gum, you change some of its physical properties—shape and size However, you haven’t changed the identity of the materials that make up the gum Each piece still tastes and chews the same

Physical Properties to Separate Have you ever licked the icing from the middle of a sandwich cookie? If so, then you’re using physical properties to identify the icing and separate it from the rest of the cookie You can use other physical properties to separate such as using a sifter to separate poppy seeds from sunflower seeds Or sand from iron fillings by using a magnet

Physical Change physical changeA physical change is any change in size, shape, or state of matter These changes might involve energy changes, but the kind of substance—the identity of the element or compound—does not change!

Physical Change Remember that when a solid changes into a liquid the atoms are not changing. Changing State is a physical change!

Physical Change to Separate In some parts of the world, water is very scarce, many such areas lie near the sea They obtain their drinking water by using the physical property of boiling point to separate the the salt from the water This process is called distillation In distillation, you use an apparatus to vaporize and condense liquid, leaving the solid material behind

Chemical Properties Have you ever seen the warning labels on paint thinners and lighter fluids that read “FLAMMABLE” Flammability is a chemical property Burning produces new substances during a chemical change

Chemical properties are properties that relate to how one substance reacts with others. Baking soda has the chemical property that it reacts with vinegar to produce carbon dioxide and water. Copper has the chemical property of reacting with carbon dioxide and water to produce a greenish-blue solid known as patina. Chemical Properties can only be observed by changing the substance which turns it into a new one. Chemical Properties

Chemical Change These two examples involve changing the way the atoms in the molecules are arranged. When a substance changes by having its atoms rearranged it is called a chemical change. The baking soda and vinegar underwent a chemical change because the atoms that made them up were rearranged into carbon dioxide and water.

How can you tell the difference? Sometimes it is difficult to tell the difference between a chemical change and a physical change Even though when water freezes it looks different than liquid water, it is still a physical change. However when iron turns to rust it too looks physically different but this is a chemical change.

The difference A physical change can often be reversed by changing the conditions. –For example to freeze water it has to be cold, once frozen the water can be turned back to liquid by changing the temperature –This is not the case for iron turning into rust. Once the iron is rusted there is no going back. –Rust is a new substance with its own properties.

Other clues There are other clues that a chemical change has taken place –You can see a flame –A gas is produced –There is a change of color –A precipitate is formed A precipitate is when two liquids are mixed and form a solid! –There is a change in odor

What is a Precipitate? A precipitate is formed when two liquids chemically react with each other to form a solid. »LinkLink

What kind of change is this?

In Review Physical properties are observed with out changing what the substance is. –Example Water freezes at 0 degrees Celsius but frozen water is still water. A physical change is often reversible and does not change the arrangement of the atoms that makes the substance up. –Example: H 2 O does not change when it freezes, melts, of vaporizes. It is still H 2 O

In Review Chemical Properties can only be observed by changing the substance and turning it into a new substance –Example: An iron nail and oxygen react to form rust which is neither iron or oxygen. It is a new substance A Chemical Change occurs when a substance’s atoms are rearranged to form a new substance –Example: Copper (a tan colored metal), carbon dioxide (a clear, odorless gas), and water (a clear liquid) react to form patina, which is a greenish solid.

In Review There are 5 signs of a chemical change –FIRE –Production of GAS –COLOR change –PERCIPITATE –ODOR