1. Unit 7: Chemical Reactions
Writing word and skeletal equations

2. Chemical Reactions:
When the atoms of one or more substances are rearranged to form different substances.
CH O ⇒ CO H2O
Reactants: Starting substances
Products: Ending Substances

3. Chemical Reaction Symbols: Write these in your flipbook
+  Separates two or more reactants or products
⇒  Separates reactants from products
↔  Separates reactants from products and indicates a   reversible reaction
(s)  Identifies a solid state
(l)  Identifies a liquid state
(g)  Identifies a gaseous state
(aq)  Identifies a water solution (Aqueous)

4. Law of the Conservation of Mass
Mass is neither created nor destroyed during a chemical reaction

5. Signs of a chemical change:
Energy change
Color change
Odor change
Production of gas
Formation of a solid (precipitate)

6. Key words for chemical reactions:
Reacts: tells us what is reacting with what
We use a + to represent reacts/reacts with
Yields/To form: tells us what the product(s) is
We use an to represent yields/produces/to form
* We state the state of the matter for each substance. (solid, liquid, gas, or aqueous)

7. Change in Energy
Energy either being gained or released as heat or light
Two types:
Exothermic: Energy released by the reaction
We will see light or feel heat
Endothermic: Energy gained by the reaction
We will feel the reaction getting cold

8. Odor Change: Color Change: Production of a gas:
Rotting, baking, cooking, etc.
Color Change:
Typically associated with another sign of a chemical change
The formation of a solid/percipitate
Note: Mixing of colors, diluting, etc, are not signs of a chemical change
Production of a gas:
Formation of bubbles, etc
This is not caused by heating or boiling a substance.

9. Formation of a Solid:
A solid is formed during the reaction, when adding or taking away energy from the rxn.
This solid is known as a precipitate.
It is NOT mean the freezing of a liquid into a solid.

10. Word Equations: Chemical Rxn in word format:
Solid Aluminum and liquid bromine react to produce solid aluminum bromide.

11. Skeletal Equations
Chemical reactions using chemical symbols/formulas and chemical reaction signs.
Written from a word equation:
Solid Aluminum reacts with liquid bromine to form solid aluminum bromide.
Al(s) + Br2(l) AlBr3(s)

12. Key Words: Remember the key words give us information about the reaction
Carbon monoxide gas and oxygen gas react to yield carbon dioxide gas.
CO(g) + O2(g) CO2(g)

13. States of Matter: (write these in your flipbook)
Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq)

14. Diatomic Elements: CO(g) + O2(g) CO2(g) Al(s) + Br2(l) AlBr3(s)
Notice that some of the elements have a 2 after them in their skeletal equations:
These are called diatomics:
These are elements that cannot exist in nature a single atom. If they are NOT in a compound, then they must be bonded to another atom of the same element  Cl + Cl = Cl2
CO(g) + O2(g) CO2(g)
Al(s) + Br2(l) AlBr3(s)

15. Diatomic Elements: Check and make sure these are correct in your flipbook
There are 7 diatomics:

16. Practice Problems:
I will complete the first one with you, then you will try the rest on your own.
You may write these right on your table, IF and ONLY IF you have a neon expo marker, if not please complete them on a separate sheet of paper.

17. Practice:
Aqueous Sodium hydroxide reacts with aqueous calcium bromide to form aqueous sodium bromide and solid calcium hydroxide.

18. Practice:
Solid zinc reacts with aqueous sulfuric acid to form hydrogen gas and solid zinc (II) sulfate.
Solid barium hydroxide decomposes into solid barium oxide and water.