Physical and Chemical Changes Mrs. Horn 5 th Grade Science

What are physical changes? Alters the form of an object without changing the type of matter it is Examples: changes in size and shape; Sharpening your pencil changes only its shape, but it is still a pencil. Tearing a sheet of paper and breaking glass are also examples of physical changes.

Changing States- Physical Change If you put a piece of ice on the counter, it will melt into a puddle. Overnight, the puddle will likely disappear as the water changes into a gas. Are these physical changes?

Changing States- Physical Changes Change of state is an example of a physical change. A substance can change from solid to liquid to gas. The substance does not its chemical identity in the process. Only its state changes. For example, ice cubes are water. When they melt, the liquid is still water. When the liquid water evaporates, it changes into a gas, but the gas particles are still water.

Reversing Physical Changes Combining two substances to make a mixture is an example of a physical change. The two substances do not lose their identities when combined and can still be physically separated. (Example: mixing sugar with water- sugar dissolves) You can reverse the formation of the above mixture by evaporating the water and collecting the vapor; the sugar will be left behind in the container.

Chemical Changes Occur when atoms link together in new ways to create substances that are different from the original substances Also known as a chemical reaction Example: Combining vinegar and baking soda- The baking soda changes and bubbles form (bubbles are a new substance). A new white substance is left behind that has properties different from those of the vinegar and baking soda.

How can you spot a chemical change? Produce new substances that have properties that are different than the previous ones Changes of color- bleach Tarnish on metal (corrosion) Releases gas- antacid Forms a precipitate (solid formed from the chemical reaction of some solutions)- soap scum Releases energy (light and heat)- burning candle

How can we use chemical changes? Plants making food Machines such as space shuttles Formation of compounds