1. Evidence of Chemical Change

2. What is a chemical change?
chemical change - matter changes into a new substance through a chemical reaction.
The animation to the right shows a chemical change. The two molecules exchange atoms, forming new substances.
Animation from:

3. Chemical Change Example: Baking Soda and Vinegar
Baking soda and vinegar are two chemicals with different physical properties
Baking soda (sodium bicarbonate) is a powdery white odorless solid
Vinegar (acetic acid) is an acidic liquid with a strong odor
NaHCO3
Sodium Bicarbonate (solid)
CH3COOHVinegar (liquid)
Think of baking soda and vinegar as two different couples dancing. The atoms stay with their own molecule when they are dancing on opposite sides of the room.

4. Chemical Change Example: Baking Soda and Vinegar
A chemical change occurs when you combine baking soda and vinegar
Atoms from one molecule are more attracted to the other molecule
The two molecules break apart and their atoms rearrange to form three new substances
NaHCO3
Sodium Bicarbonate (solid)
CH3COOHVinegar (liquid)
The two dancing couples split apart and switch partners when they get too close

5. Chemical Change Example: Baking Soda and Vinegar
A chemical change occurs when you combine baking soda and vinegar
The baking soda and vinegar molecules break apart and their atoms rearrange to form new substances
No atoms were created or destroyed – only rearranged
The reaction produces three new substances and an exothermic* temperature change
C2H3NaO2 Sodium Acetate (solid)
CO2
Carbon Dioxide (gas)
H2O
Water (liquid)
The dancing couples split apart and dance with new people instead. That’s cold!*

6. Why is the reaction of baking soda and vinegar such a great example of a chemical reaction?
We know that a chemical change occurs when you combine baking soda and vinegar because there is evidence
Two reactants are combined:
Vinegar (acetic acid) is a transparent colorless liquid with a strong odor
Baking soda (sodium bicarbonate) is a white powdery solid with a salty taste
Three new substances with different properties are produced:
Carbon dioxide gas is colorless and odorless (gas produced)
Water is colorless and odorless liquid (liquid produced)
Sodium acetate is a white solid precipitate (solid precipitate forms)
There is an endothermic temperature change, which means the reaction gets cold

7. Evidence of Chemical Change
We will discuss four signs of chemical reactions in 6th grade science
1. Formation of a gas
2. Color change
3. Temperature change
4. Formation of a solid precipitate

8. Evidence of Chemical Change
1. Production of a Gas
You might see small bubbles (fizz) or large bubbles when a gas is produced. You might be able to hear the gas bubbles popping
Be careful! Bubbles don’t always mean that a chemical change occurred. You can see and hear bubbles when you open a soda can, but that is not a chemical reaction.

9. Evidence of Chemical Change
2. Color Change
Color is a property of chemical substances. You might see a new color when atoms and molecules rearrange after a chemical reaction
Be careful! Different colors don’t always mean that a chemical change occurred. You can see a new color when you add food coloring to frosting, but that is not a chemical change!

10. Evidence of Chemical Change
3. Change in Temperature
Chemical reactions can result in an increase or decrease in temperature
Exothermic reactions get hotter (EXO = HOT)
Endothermic reactions get colder (ENDO = COLD)
Be careful! Changing temperatures don’t always mean that a chemical change occurred. You can melt ice cream in the sun or freeze it in the freezer, but those are not chemical changes!

11. Evidence of Chemical Change
4. Production of a Precipitate
A new solid forms
The solid comes out of a liquid solution because it does not dissolve
The solid usually falls to the bottom of the beaker
Be careful! The formation of a solids does not always mean a chemical reaction occurred. Putting water in the freezer causes the water to become a solid, but that is not a chemical reaction!

12. Is it a Chemical Change? Test your knowledge!
Write CHEMICAL if the example is a chemical change.
Write PHYSICAL if the example is a physical change.
List evidence to support your answer
For example: Adding sprinkles to ice cream is a PHYSICAL CHANGE because the mixture can be separated and the substances retain their original properties
For example: Adding baking soda to vinegar is a CHEMICAL CHANGE because a gas is produced, a solid precipitate forms, and the reaction is endothermic

13. Is It a Chemical Change?
A forest fire destroys acres of land. There is a lot of heat and smoke, and the trees turn to charcoal.
ANSWER: CHEMICAL CHANGE
EVIDENCE: Gas produced – Smoke
Color change – wood to charcoal
Temperature change - exothermic

14. Is It a Chemical Change?
When making hot cocoa, transparent colorless water turns brown when you mix in the cocoa powder.
ANSWER: PHYSICAL CHANGE
EVIDENCE: The water is turning brown because the cocoa is brown. Both substances retain their original properties and the mixture can be separated

15. Is It a Chemical Change?
An iron wheelbarrow is left out in the rain and the meal rusts, producing iron oxide.
ANSWER: CHEMICAL CHANGE
EVIDENCE: Color change – new reddish brown color
Precipitate – rust is a new solid

16. Is It a Chemical Change?
On a hot day, water droplets form on the outside of a cold glass of ice water.
ANSWER: PHYSICAL CHANGE
EVIDENCE: Condensation is a phase change. Water molecules from the air condense on the cold glass. No new substance is formed.

17. Is It a Chemical Change? Ice cream melts after it falls on the ground.
ANSWER: PHYSICAL CHANGE
EVIDENCE: Melting is a phase change. Solid ice cream turns into a liquid when heat is added. No new substance is formed.

18. Is It a Chemical Change?
A raw egg cooks in a frying pan. The transparent colorless egg white solidifies and turns white. The yellow yolk solidifies.
ANSWER: CHEMICAL CHANGE
EVIDENCE: Color change – colorless to white
Precipitate forms - the egg white and yolk solidify when heated

19. Is It a Chemical Change?
Chalky white solid Alka- Seltzer tablets contain baking soda and citric acid. Alka-Seltzer tablets fizz when dropped into water.
ANSWER: CHEMICAL CHANGE
EVIDENCE: Gas formation – the fizz you see is the result of gas bubbles

20. Is It a Chemical Change? Crayons change white paper to red.
ANSWER: PHYSICAL CHANGE
EVIDENCE: The paper is turning red because the crayon is red. No new substance is formed.

21. Is It a Chemical Change?
Soda fizzes, and bubbles rise as you pour it in a glass.
ANSWER: PHYSICAL CHANGE
EVIDENCE: The bubbles were already there, dissolved under pressure in the bottle. No new substance was formed.

22. Is It a Chemical Change?
When you crack a glow stick, the chemicals inside combine to produce a small amount of heat and carbon dioxide gas along with bright glowing light.
ANSWER: CHEMICAL CHANGE
EVIDENCE: Temperature change - exothermic
Gas produced – carbon dioxide gas is a new substance