Physical and chemical changes Physical changes involve a change in size, shape, or state. Chemical changes produce new kinds of matter

Physical changes Suppose you are playing baseball with friends. You hit a home run right through the garage window. The glass shatters into hundreds of tiny pieces. Your baseball has caused a physical change in the window glass. A physical change is a change in the size, shape, or state of matter that does not change it into a new kind of matter.

Physical changes include Cutting Tearing Folding Breaking Shattering Melting freezing When the glass was broken by the baseball, the tiny pieces of glass still had the same properties. It was still glass.

Physical Changes What happens to a popsicle when you leave it outside? It melts! The melted parts look different than the frozen parts. However, if you taste one of the juice bars, you would observe that the melted and frozen parts taste the same. Melting and freezing does not form a new kind of matter. Melting and freezing is a physical change

Common Physical changes When matter is moved or changed, energy is always involved Energy is the ability to cause change. Sometimes energy must be added to matter to cause a change. For example, a glue stick melts in a hot glue gun when heat is added Heat is one source of energy.

Common physical changes Think about physical changes that happen around you every day Melting Ice breaking glass building a sand castle These changes in form, size, and shape cannot occur without energy Heat from the sun melts ice Energy of a moving baseball breaks glass You use energy in your muscles to press sand into a sand castle

Chemical changes Have you ever made a cake before? What ingredients do you need to bake a cake? You need eggs, flour, water, oil, sugar When you mix the ingredients together, it looks very different than when you started. Then, after baking, it looks different again. Can you taste the eggs after you bake a cake? Not usually! After you bake a cake, it looks different from the way it looked before. The properties of the flour, sugar, oil, and eggs have also changed. Baking a cake is not a physical change. It is a chemical change.

Chemical change A chemical change is a change in matter that produces new kinds of matter with different properties. Energy is always involved in a chemical change When you bake a cake, energy is taken in by the batter to produce a new kind of matter.

Atoms and molecules Chemical changes involve particles of matter, such as atoms and molecules. In a chemical change, atoms and molecules do not just rearrange themselves. They break apart and form new combinations with atoms and molecules. This causes new matter. Atoms and molecules form these new combinations in a chemical reaction Chemical reaction is another word for a chemical change.

Common chemical changes Every time you ride in a car, you depend on chemical changes. When you start the car, a chemical reaction in the car battery produces electricity that starts the car. Then the car engine burns gasoline, a chemical reaction that produces energy to move the car. The exhaust includes the products of burning gasoline

Common chemical changes Chemical changes happen all around us Wood burning Fireworks Rusting metal Your body changes food in chemical reactions to give you the substances and energy you need to grow

Clues of a chemical change Change in color Change in state of matter change in temperature Change in odor Change in energy Gases forming (bubbles)

Comparing physical and chemical changes Matter can change physically and chemically. In a physical change, no new kind of matter is formed. It might look different, it is still the same In a chemical change, a new kind of matter is always formed. It looks different and has different physical properties. Lets look at page 212 and 213 in our science book to compare chemical and physical changes.

Conserving Matter When there is a chemical or physical change, the amount of matter stays the same. Matter is always conserved. It is neither created nor destroyed. In a chemical change, this means that the mass of the materials before a chemical change is equal to the mass afterwards. This is true even if you cannot see the materials that form, such as when a gas is produced. Matter is also conserved in a physical change. Place liquid water in the freezer, and it undergoes a physical change to become ice. Yet the mass of the water is unchanged.