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What do you already know about chemical and physical changes?
What do you already know chemical reactions?
Warm Up: Write in your notes
Chapter 9: Chemical Reactions
Writing word and skeletal equations
When the atoms of one or more substances are rearranged to form different substances.
Chemical Reactions:
CH4 + 2O2 ⇒ CO2 + 2H2O
Reactants: Starting substances Products: Ending Substances
+ 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)
Chemical Reaction Symbols:
Mass is neither created nor destroyed during a
chemical reaction
Law of the Conservation of
Mass
1. Energy change2. Color change3. Odor change4. Production of gas5. Formation of a solid
(precipitate)
Signs of a chemical change:
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
Energy Change
Typically associated with another sign of a chemical change◦ Mixing of colors, diluting, etc, are not signs of a
chemical change
Color Change:
Rotting, baking, cooking, etc.
Odor Change:
Formation of bubbles, etc
◦ This is not caused by heating or boiling a substance.
Production of Gas
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.
Formation of a Solid:
Chemical Rxn in word format:
Solid Aluminum and liquid bromine react to produce solid aluminum bromide.
Word Equations:
Chemical reactions using chemical symbols and an arrow.
Al(s) + Br2(l) AlBr2(s)
Skeletal Equations
They are two different ways to write the same thing.
Solid Aluminum and liquid bromine react to produce solid aluminum bromide.
Al(s) + Br2(l) AlBr2(s)
Word and Skeletal Equations:
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
Key Words:
Carbon monoxide gas and oxygen gas react to yield carbon dioxide gas.
CO(g) + O2(g) CO2(g)
Key Words:
Solid (s) Liquid (l) Gas (g) Aqueous (aq)
◦ Use the context clues of the word equation to determine the states of matter of the reactants and products.
States of Matter:
Notice that some of the elements have a 2 after them in their skeletal equations:
These are called diatomics:◦ These are elements exist in nature as two atoms
of the same element together, ONLY when they are not bonded to another element.
Diatomic Elements:
CO(g) + O2(g) CO2(g)
Al(s) + Br2(l) AlBr2(s)
There are 7 diatomics:
Diatomic Elements:
Aqueous Sodium hydroxide reacts with aqueous calcium bromide to form aqueous sodium bromide and solid calcium hydroxide.
Practice:
Solid zinc reacts with aqueous sulfuric acid to form hydrogen gas and solid zinc (II) sulfate.
Practice:
Fe(s) + O2(g) Fe203(s)
Practice:
Solid calcium oxide reacts with water to form solid calcium hydroxide.
Practice:
Gaseous sulfur dioxide and oxygen gas react to form sulfur trioxide gas.
Practice:
Solid sodium reacts with chlorine gas to form solid sodium chloride.
Practice:
NaCl(aq) + AgNO3(aq) NaNO3(aq) + AgCl(s)
Practice:
Please complete your ticket out the door, and turn into me before packing up.
HINT: Make sure you know the 7 diatomic elements tomorrow when you come in the door!
Ticket out the door: