1. Chemical Reactions
Chapter 7.1

2. Objectives
Recognize some signs that a chemical reaction is taking place.
Explain chemical changes in terms of the structure and motions of atoms and molecules.
Describe the differences between endothermic and exothermic reactions.
Identify situations involving chemical energy.

3. Signs of a Chemical Reaction
Release of gas
Change in color
Change in odor
Release of energy

4. Release of Gas

5. Change in Color

6. Change in Odor

7. Release of Energy

8. Explain why the following are examples of a chemical reaction.
Lighting a match
Mixing vinegar and baking soda
Grilling a burger
Food rotting

9. Chemical Reactions
Involves rearrangement of atoms. The number and types of atoms are conserved.
Chemical Change
Example: In a car or boat engine, isooctane (C8H18) and oxygen (O2) react to form water (H2O) and carbon dioxide (CO2).

10. Chemical Reactions
Reactant – a substance that undergoes a chemical change.
Product – a substance that is the result of a chemical change.

11. Predict which atoms will be found in the products of the following reactions.
Mercury (II) oxide, HgO, is heated and decomposes
Hg and O
Limestone, CaCO3, reacts with hydrochloric acid, HCl
Ca, C, O, H, and Cl
Table sugar, C12H22O11, burns in air to form caramel
C, H, and O

12. Energy and Reactions Energy must be added to break bonds.
You need a spark to react gasoline and oxygen so that you can break apart the bonds within the gasoline and oxygen.
Energy is released when forming bonds.
After you have broken the bonds between the gasoline and oxygen, they will form new bonds to create carbon dioxide and water and energy will be released.

13. Energy and Reactions
The chemical energy of reactants is equal to the chemical energy of the products.
Chemical energy – the energy stored within atoms and molecules that can be released when a substance reacts

14. Energy and Reactions
Exothermic reaction – a reaction that transfers energy from the reactants to the surroundings usually as heat. Energy is released.
Taken from

15. Energy and Reactions
Endothermic reaction – a reaction in which energy is transferred to the reactants usually as heat from the surroundings. Energy is absorbed.
Taken from

16. Critical Thinking:
Calcium oxide, CaO, is used in cement mixes. When water is added, heat is released as CaO forms calcium hydroxide, Ca(OH)2.
What signs are there that this is a chemical reaction?
Which has more chemical energy, the reactants or products?
Explain your answer.

17. Identify which of the following is a chemical reaction
Melting ice
physical
Burning a candle
Chemical reaction
Rubbing a marker on paper
Rusting iron

18. List four forms of energy that might be absorbed or released during a chemical reaction.
Heat, electricity, light, sound
List three signs that could make you think a chemical reaction might be taking place.
Change in color, release of gas, release of energy, change in odor

19. Classify the following as exothermic or endothermic.
Paper burning with a bright flame
* exothermic
Plastics becoming brittle after being left in the sun
* endothermic
A firecracker exploding