Physical and Chemical Properties and Changes

Properties The properties of a substance are those characteristics that are used to identify or describe it.  A property of the elements iron, nickel, cobalt, and gadolinium is that they are strongly magnetic.

When we say that water is "wet", or that silver is "shiny", we are describing materials in terms of their properties.  A property of the mineral jade is its green color.

Properties can be divided into the categories of physical properties and chemical properties. A chemical property of water is that it is the universal solvent. It dissolves more substances than any other liquid. A physical property of water is that it freezes at 32 degrees Fahrenheit.

Examples of physical properties are:

Color These minerals are identifiable by their color properties.

Freezing Point The freezing point of carbon dioxide is -109 degrees Fahrenheit.

Boiling Point The boiling point of water at sea level is 212 degrees Fahrenheit. It drops almost 2 degrees Fahrenheit for every thousand feet of elevation above sea level.

Melting Point The melting point of wax is 128 degrees Fahrenheit.

Opacity Opacity is the state of being impenetrable to light. Obsidian is a natural opaque glass. Window glass is on the other side of the opacity scale. It is transparent.

Viscosity Viscosity is the measure of a fluid's resistance to flowing. Honey flows slowly. It is much more viscous than milk.

Density Density is a measure of how much mass is contained in a given volume. Iron is a dense element. Styrofoam is not very dense. A Styrofoam ball the same size as the iron meteor pictured above would be much lighter than the meteor. Air is even less dense than Styrofoam.

Hardness A diamond is the hardest known natural substance. Gypsum is so soft you can scratch it with your fingernail.

Physical properties are readily observable Physical properties are readily observable. What physical properties can you observe here:  

Chemical Properties

Chemical properties are only observable during a chemical reaction Chemical properties are only observable during a chemical reaction.  For example, you might not know if sulfur is combustible (extremely flammable) unless you tried to burn it. (Don’t do this!)   Sulfur burns with a blue flame

Chemical properties include:

Ignition Temperature The ignition temperature is the lowest temperature at which a substance will begin to burn. The ignition temperature for paper is reported to be 451 degrees Fahrenheit.

Reactivity with Water Iron reacts with water to form rust. Some alkali metals (like sodium) react with water to form toxic fumes or even produce heat and combustion!

PH Factor The pH factor is the measure of acidity. Sodas, lemons and limes have a high pH factor. The opposite of an acid is a base. Baking soda is an example of a weak base. Water has a neutral pH factor.

Physical Changes In a physical change there is only a change of state. The properties of the substance remain the same and No new substance is produced. The sublimation of dry ice is an example of a physical change.

Lava cooling to form stone is a physical change.

A log being chipped into mulch is a physical change.

A Popsicle melting is a physical change

An egg breaking is a physical change.

Describe physical changes pictured in the collage below:

Chemical Changes

In a chemical change one or more NEW substances are created In a chemical change one or more NEW substances are created. The new substance is different from the original. It has properties that are different than those of the starting materials. After a chemical change, you cannot get the original substances back easily. Vinegar and baking soda react to produce a chemical change. A new substance – carbon dioxide – is produced during this chemical change.

Examples of chemical changes include:

Tarnishing The tarnish on this silver bowl is the result of a chemical change. The silver reacted with sulfur in the air to create a new substance: tarnish. You can clean the bowl, but you cannot change the tarnish back into the elements silver and sulfur.

Oxidation Oxidation is a chemical change in which oxygen reacts with a metal or even an organic substance. Metal rusting, a freshly-cut apple turning brown, and a copper penny turning green are all examples of oxidation.

Decomposition Decomposition is a chemical change. It is the breakdown of organic matter by bacteria, fungi, and other organisms.

Cooking Cooking can cause a chemical change, such as turning batter into cake.

Or a raw egg into a cooked one.

Combustion Before After Combustion is a process in which a substance reacts with oxygen to give heat and light. Combustion can cause a chemical change, turning paper into ash.

Describe chemical changes pictured in the collage below:

So…what have we learned? Take the quiz at the link below to find out. http://www.quia.com/quiz/303980.html

It’s time for some labs on physical and chemical changes.