Properties and Changes of Matter Chapter 20

Physical Property A physical property is a characteristic that you can observe without changing. How something looks, smells, sounds, or tastes are all examples of physical properties

Using Your Senses You can detect many physical properties with your senses. For example, you can see the color and shape of an object. You can also touch it to feel its texture.

Physical States Perhaps you are most familiar with the three states of water.

3 States of “water” Solid (ice) Liquid (water) Gas (steam)

Physical Properties Another physical property is mass. Weight is not dependent on mass. Size does not determine mass.

Size Dependant Properties Density measures the amount of mass in a given volume. To calculate the density of an object, divide its mass by its volume.

Density Density is equal to mass divided by volume or D=M/V Another way to look at it would be to think of the “Density Heart”.

Solubility Solubility also does not depend on size. Solubility is how a solute (sugar, salt, etc) dissolves into a solvent (for example sugar dissolves into coffee or tea).

Saturatation Point Once a solvent can’t hold anymore, it is saturated. If a solvent holds a large amount of a solute, it is concentrated.

Increasing solubility One way to increase solubility is to heat up the solvent.

Melting and Boiling Point The temperature at which a solid changed into a liquid is called its melting point. The temperature at which a liquid changes into a gas is called its boiling point.

Lava flowing video Another video Do rocks have a melting point? Do they have a freezing point? Lava flowing video Another video

Physical Change A physical change is one in which the form or appearance of matter changes, but not what it’s made of. A frozen lake is still made up of H2O.

Physical Change Crumpling a sheet of paper into a ball causes a physical change.

Chemical Property A chemical property is a characteristic that cannot be observed without altering the substance. For example, the ability to burn is a chemical property.

Chemical Change During a chemical change, substances are changed into different substances. Fireworks is an example of a chemical change.

When iron in steel is exposed to oxygen and water in air, iron and oxygen atoms combine to form the principle component in rust.

Signs of a Chemical Change A change in color has occurred. Rust, leaves in fall, or a half-eaten apple. A change in energy. Food as it is cooked, or fireworks.

Energy Energy is released when sodium and chlorine are combined and ignited. Now, let’s watch a video.

Endothermic vs. Exothermic When heat is given off by a chemical reaction, it is called an exothermic reaction. When heat is absorbed during the reaction, the reaction is called an endothermic reaction. Instant ice packs or instant hot packs are everyday example of endothermic and exothermic reactions.

Odor When you smell food that has spoiled, you know a chemical change has taken place.

Gases or solid The formation of a gas is a clue to a chemical change.

Not Easy to Change The substances produced during a chemical change cannot be changed back into the original substances by physical means. Physical changes can be changed back. Wood that has changed into ashes and gases cannot be restored to its original form as a log.

Chemical vs Physical In a physical change, what something is made of does not change. In a chemical change, what something is made of does change.

Law of Conservation of Mass Regardless of whether it’s a physical or chemical change, the mass stays the same. This is known as the law of conservation of mass.

Burning Wood If wood is burned, does it weigh the same? The answer is YES!!! If you weigh the ashes and gas.