Take a peek into your kitchen. Did you know it's a hot bed of chemical and physical changes? This definition of chemical change will help clarify the concept of changing matter. Read on for more information about the changes that are happening all around--and within--you.
Properties of Matter
Everything--the human body, hamsters, ketchup, spoons, soda--is made of matter. We describe and categorize different types of matter by referring to its physical or chemical properties.
Physical properties are the traits of an object that can be readily seen such as size, color and state. Measuring or changing these properties does not affect the chemical nature of the matter. For example, a paper that is cut into small pieces has undergone a physical change. The pieces have a different quantity, size, shape and texture than the original sheet.
Chemical properties are the characteristics that describe the composition of matter. These traits are carried by each individual atom, or part of matter. Some examples of chemical properties include combustibility, flammability and reactivity. Another way to look at this is to think of the chemical properties as potentials. Dry paper has the potential to burn; this is flammability, a chemical property. Magnesium metal has the potential to combine with oxygen and form Magnesium Oxide.
Physical and chemical traits are constantly changing in reaction to the environment. Bread gets moldy. Sneakers wear out. Statues rust. The changes that occur are called either physical or chemical changes, depending on the trait that is being altered.
Practice: Categorize the following items as descriptions of either a physical property, chemical property, physical change or chemical change.
The ball is red.
Water is hot.
A paper can burn.
The firework exploded.
The leaves turned color in Autumn.
Sugar dissolves in a cup of water.
The bicycle has rusted.
The apple has spoiled.
I crumpled the newspaper.
The glass vase shattered and cannot be fixed.
Physical changes are usually easy to identify because they visibly alter matter. When ice melts, changing physical states, you can see water pooling in its place. When a crayon is used to draw, the crayon breaks into millions of tiny pieces and adheres to the paper. The color of the crayon, in your hand and on the drawing, is the same; only the size and shape of the matter has changed.
Think About It...
Identify four physical changes that occur in your kitchen. Need some help? Here are some examples of physical changes.
Boiling water evaporates.
The paper towels roll is built to undergo physical change--perforations make it easy to rip into smaller pieces.
A sponge can expand when it soaks up water, or shrink as it dries.
Chemical changes occur at the atomic level, which means we can't actually see them happening. However, we can use all of our senses and other scientific meters to detect a chemical reaction as it occurs. There are three main signs to look out for when trying to identify a chemical change. They will not always signify the occurrence of a reaction, but they are often linked with chemical changes.
the appearance of a new substance,
irreversible change has occurred
the absorption or release of energy.
Different types of chemical changes have names that describe the processes occurring. Here are some you might know.
Think About It Some More...
Go back to the kitchen. Try to find two chemical changes that have occurred or will occur. Remember that chemical properties describe the potential for a reaction and change. It's your job as a science detective to put the pieces together and see the possibilities. Here are some examples.
Bread molding--Don't get confused, but there are two chemical changes going on here. Mold, a living organism, is consuming the sugar, water and minerals in the bread. And the bread is decomposing. These changes are irreversible, release smelly gases and produce a small amount of heat.
Cake baking--When you bake a cake you are combining several ingredients into a solution, adding energy (heat) and making a new (and delicious) material that cannot be returned into the original ingredients.
Atom - the smallest unit of matter that contains chemical properties
Chemical Change - the result of a reaction which creates one of more substances with different chemical properties
Chemical Property - the chemical traits of matter or the potential of matter to react in a particular way
Matter - any object or substance that 1) takes up space and 2) has mass
Physical Change - a visible, quantifiable, generally reversible alteration of the physical state of matter
Physical Property - the corporeal definition of matter, a description of the state of a particular matter
What Are Chemical Properties And Chemical Change?--This site has some great experiments you can try at home. (http://www.elmhurst.edu/~chm/vchembook/105Achemprop.html)
Mold Pamphlet--Learn more about mold (http://www.aehf.com/articles/mold-pamphlet.htm)
NYU: What Is Matter?--(http://www.nyu.edu/pages/mathmol/textbook/whatismatter.html?inputbox=yellow)
The Matter With Matter--A philosophical discussion of matter (http://www.exploratorium.edu/worldwidewebcast/matter.html)