Chemical Changes

Essential Questions What are chemical changes? How do I recognize chemical changes?

Chemical Changes A Chemical Change is a change that results in one or more new substances. When a new substance is formed, it can never return to its original state. Take a match and light it. You’ll notice the red tip turns black once a flame has been ignited. Can you ever take a lit match and turn it back to its original state? NO! This is because a chemical change has taken place. Take an egg and fry it in a skillet. Once the egg is cooked, can you ever make it a runny egg again? NO! This means a chemical change has taken place.

Recognizing a Chemical Change Color Change Ex. Rust Changes from a color to reddish-brown Smell Ex. Eggs rotting Gives off a terrible smell Substance Given Off Ex. Wood Burning Smoke is released into the air

Car For Sale? What caused this? Rust is a… CHEMICAL REACTION We all know that this car has several problems. Look at the color- it used to be yellow from what we can tell. Now it is a rusty brown. What caused this? Iron in the metal reacts with oxygen in the presence of water to form rust. Rust is a… CHEMICAL REACTION

Is it a Chemical Change? YES! YES! A Rotten Egg… A Rusty Nail… It changed color- it was silver and hard, now it’s brittle and a reddish brown It has a terrible odor! Remember, anything that gives off an odor is a chemical change.

Is it a Chemical Change? YES! YES! Fireworks… Burnt toast… It not only changed color from its original state, but it also gives off smoke after being lit. It has a terrible odor and it changed colors. A burnt piece of toast can never be turned back into the soft piece it once was.

Fire, Fire!!! Believe it or not, every time wood burns, a chemical change takes place. Not only is there a color change, but smoke is released into the air. Wood that is burnt can never be restored into its original state. This is why we’re always left with ash.

Let’s Bake some bread! What happened? Baking caused a chemical change. You can never take a baked loaf of bread and turn it back into dough.

Let’s Review Which always happens during a chemical change? A. Matter disappears B. A smell is produced C. A gas is formed D. A new substance is formed D.

Let’s Review Substance Reaction Acid changes the color of metal, Vinegar (acetic acid) Penny turned green Water Penny remains the same Lemon Juice (citric acid) Look at the table. What conclusion can you draw about how substances affect pennies? Acid changes the color of metal, therefore a chemical change has taken place.

Compare/Contrast Suppose you bake a loaf of bread. Suppose you draw with marker on paper. How are the changes in color that occur different from one another?