Chapter 20 – Section 2 Physical and Chemical Changes Open books to page 600 Please take notes over the yellow slides!

Introduction  Look at the picture in figure 7 on page 600.  The artists will eventually turn the lump of clay into pottery.  Has the clay gone with a physical or chemical change? How do you know?

Physical Change  The clay goes through a physical change. The clay is now a different shape BUT is still the same composition.

Physical Changes  Physical Change – the form or appearance of the matter changes, but not its composition.  Physical changes can be reversed. (If you break a pencil in half, you can put it back together easily)  Whenever you cut, tear, grind, or bend matter you are causing a physical matter.

Physical Change  When you change the shape of matter, but not the composition, you are causing a physical change.  Examples  crumpling up a piece of paper (composition is the same, shape is different.  Cutting up fruit (composition is the same, shape is different)  Digestion (when in the mouth - Chewing)

Physical Change  When you dissolve something into a substance, it’s a physical change  Examples  When you add sugar to iced tea, the sugar dissolves into the tea and spreads out throughout the liquid that’s why you can taste the sweet sugar. The composition of the sugar is still the same, only the form of the sugar has changed.

Physical Change  When matter changes state, a physical change occurs  Examples  when ice melts, it becomes water. The composition is still the same, BUT the matter is in a different form. It’s still water.  when water freezes from liquid to solid

Chemical Change Chemical change – substances are changed into different substances. This change is not easily reversed because the composition of the substance changes. Example – fireworks on the forth of July are created by chemical changes.

Chemical Change Indicators How do you know a chemical change has occurred?? There are five common indicators I like to use the following acronym to help me remember.. GIRL SCOUTS LIKE HOT CHOCOLATE

Indicator #1 G (Girl) – is a gas produced? To determine if a gas has been produced, look for bubbles Example – Alka Seltzer in water creates a gas.

Indicator #2 S (Scouts) – is a solid produced? Sometimes when you mix two things together a new solid is produced. This new solid is a precipitate Exp – Rust is a result when water and iron are exposed to oxygen

Indicator #3 L (Like) – is light produced? When a firefly lights up a chemical reaction is taking place and light is produced. When you break open a glowstick and new light is produced.

Indicator #4 H (Hot) – is heat produced? When fuel is burned in a camping stove, light is produced..so is heat

Indicator #5 C (Chocolate) – is there a color change? When bananas ripen from green to yellow and then to brown a chemical change takes place When leaves change color a chemical change takes place

Indicators GIRL – Gas SCOUTS – Solid LIKE – Light HOT – Heat CHOCOLATE – Color change GIRL SCOUTS LIKE HOT CHOCOLATE!

Digestion One last word about digestion… Digestion is a chemical and physical change. When chewing, the apple is being torn and ground up. This is a physical change. When in the mouth, enzymes start to break down the apple AND the apple chemically changes as it moves through the digestive system. This is a chemical change.

Law of Conservation of Mass Remember this law – Matter is not created or destroyed When matter goes through chemical changes, matter is not lost or created. The particles may just be in a different order or arrangement.