Chapter 6:
CHEMICAL REACTIONS &
EQUATIONS
What are some signs
that a chemical reaction
has occurred?
Color Change* and
Precipitate Formation
Change in Energy
Change in Energy
• x
•
•
•
•
Change in Odor
Heat
Light
Electricity
Sound
Gas Evolution
CHEMICAL REACTIONS
1.Bonds break
2.Atoms are rearranged
3.NEW SUBSTANCE(S) with new properties
are created
The “stuff ” that you start with:
REACTANTS.
The “stuff ” that you have at the end:
PRODUCTS.
Formation of Water
Hydrogen Gas (H2) & Oxygen Gas (O2)(diatomics)
H
H
O
O
H
H
Formation of Water
Break bonds in H2 and O2
H
H
H
O
O
H
Formation of Water
Rearrange atoms & make new bonds in H2O
H2 + O2 → H2O
H
O
H
H
H
O
Think…
What some other chemical reactions that
you have seen/experienced?
• photosynthesis
• digestion
• metal rusting
• ??
Word Equations
Iron + oxygen à iron (III) oxide
Sodium bicarbonate + Acetic acid à
sodium acetate + water + carbon dioxide
• + in between compounds
• à separates reactant & product
• “yields”
Symbols
Sodium bicarbonate + Acetic acid à sodium
acetate + water + carbon dioxide
NaHCO3(s) + HC2H3O2(aq) à NaC2H3O2(aq) +
H2O(l) + CO2(g)
(s) – solid
(l) – liquid
(g) – gas
(aq) – aqueous solution
(dissolved in water)
Lavoisier’s
Law of Conservation of Mass
• Mass cannot be created or destroyed, but
it can change forms (get rearranged)
• Same number of atoms of each element
on both sides of the “yield” sign. (à)
Coefficients v. Subscripts
• Ex: 2 NaCl
• Can be changed to
balance a reaction
• Ex: H2O
• Cannot be changed
during balancing
H
Na
Cl
O
H
Na
Cl
How can we balance this equation?
NaOH(aq) + CO2(aq) à Na2CO3 (s) + H2O(l)
2NaOH(aq) + CO2(aq) à Na2CO3 (s) +
H2O(l)
How can we balance this equation?
H2(g) + O2(g)
2H2(g) + O2(g)
à H2O(l)
à 2H2O(l)
Word Equationsà
Chemical Equations
Sodium metal + chlorine gas à
sodium chloride crystals
Na(s) + Cl2(g) àNaCl(cr)
2Na(s) + Cl2(g) à2NaCl(cr)
Word Equationsà
Chemical Equations
Propane gas (C3H8) + oxygen gas à
carbon dioxide gas + water vapor +
energy
C3H8(g) + O2(g) à
CO2(g) + H2O(g) + energy
Word Equationsà
Chemical Equations
Zinc metal + hydrochloric acid à zinc
chloride solution + hydrogen gas
Zn(s) + HCl(aq) àZnCl2(aq) + H2(g)
Zn(s) + 2HCl(aq) àZnCl2(aq) + H2(g)
Types of chemical reactions
1. Synthesis/Direct Combination:
Ex:
2Na + Cl2 ➡ 2NaCl
Types of chemical reactions
2. Decomposition reaction –
Ex: “Electrolysis” of water
2H2O ➡ 2H2 + O2
Types of chemical reactions
3. Single Replacement/Displacement:
Ex:
3CuCl2 + 2Al ➡ 2AlCl3 + 3Cu
Types of chemical reactions
4.Double Replacement/Displacement:
Ex:
AgNO3 + NaCl ➡ AgCl + NaNO3
Types of chemical reactions
5. Combustion:
Ex: Burning methane (natural gas)
CH4 + O2 ➡ CO2 + H2O
Reactions that
RELEASE and ABSORB energy
• EXOTHERMIC
• Feels warm
• Energy is a product
• ENDOTHERMIC
• Feels cold
• Energy is a reactant
Question 1:
When a chemical reaction occurs,
atoms are never_______________.
A. ionized
B. rearranged
C. destroyed
D. vaporized
Question 2:
In an exothermic reaction, ________.
A. energy is conserved
B. the container will feel warm as the
reaction is occurring
C. energy is released
D. all of the above
Question 3:
A+B àAB is an example of a ________.
A. synthesis reaction
B. decomposition reaction
C. Single-displacement reaction
D. Double-displacement reaction
E. Redox reaction
Question 4:
In the equation of a chemical reaction,
the arrow means________.
A. equals
B. is greater than
C. yields
Question 5:
Which of the following is not a type of energy
that is released when a chemical reaction occurs:
A. light
B. change in color
C. sound
D. electricity
Practice
Classify the following reactions as one of
the five types.
1. 2H2O ➡ 2H2 + O2
2. 3CuCl2 + 2Al ➡ 2AlCl3 + 3Cu
3. S8 + 8O2 ➡ 8SO2 + heat
4. 2NaHCO3 ➡ Na2CO3 + H2O + CO2
5. C6H12O6 + O2 ➡ CO2 + H2O
Outline – Chapter 6 Section 3, p. 210
¤ Nature of Reactions
¤ Reversible Reactions
¤ Equilibrium
¤ Changing direction
¤ Adding reactants or energy
¤ Reaction Rates
¤ Activation energy
¤ Speed of reaction
¤ Effect of temperature,Concentration,Catalysts
¤ Slowing down reactions
Reversible Reactions
Dynamic Equilibrium
http://
www.teamestrogen.com/
content/asa_trackstand
Dynamic Equilibrium
http://www.solcomhouse.com/hydrologiccycle.htm
Dynamic Equilibrium
¤What does dynamic equilibrium mean?
¤Write your own definition
¤PCl5(g) ↔ PCl3(g) + Cl2(g)
Think about the states
of matter in this
reaction. What
condition do you think is
needed to make sure
the reaction can reach
equilibrium?
http://dluetgens.com/equilibrium_answers.html
Equilibrium
¤What will you observe when a
reaction has gone to “completion”?
¤Reactants stop disappearing
¤Products stop forming
¤If a rxn. goes to completion, is it at
equilibrium?
Blue Bottle Demo
Le Chatelier’s Principle –
Changing the Direction of a Reaction
Sulfuric Acid reacts with potassium hydroxide
to produce potassium sulfate and water.
H2SO4(aq) +2KOH(aq) ⇔ K2SO4(aq) + 2H2O(l)
Le Chatelier’s Principle –
Changing the Direction of a Reaction
H2SO4(aq) + 2KOH(aq) ⇔ K2SO4(aq) + 2H2O(l)
¤Remove a product
¤rxn. proceeds à
“favors products”
¤If products build up
¤ rxn. will ß
“favors reactants”
¤Remove a reactant
¤ rxn. will ß
Le Chatelier’s Principle –
Changing the Direction of a Reaction
H2SO4(aq) + 2KOH(aq) ⇔ K2SO4(aq) + 2H2O(l)
Reactants
Products
Types of reactants and products
Sodium chloride and silver nitrate solutions react
to form a silver chloride precipitate and an
aqueous product.
NaCl(aq) + AgNO3(aq) ßà NaNO3(aq) + AgCl(s)↓
¤Precipitates (insoluble product)
¤isolated from the rest of the rxn.
¤if a product precipitates, it is like the
product is being removed
¤ the rxn goes à
Types of reactants and products
Calcium carbonate decomposes into
calcium oxide solid and carbon dioxide
CaCO3(s) ßà CaO(s) + CO2(g)↑
¤Gas
¤isolated from the rest of the rxn.
¤if a product is a gas, the rxn goes à
**remember, with gases, the system must be closed, or the
reaction will go to completion
Types of reactants and products
¤Energy
3C + 2Al2O3(s) + energy ß à 4Al(l) + 2CO2(g)↑
¤If we heat this reaction, which direction will
the equilibrium favor?
Types of reactants and products
¤Energy
N2(g) + 3H2(g) ß à 2NH3(g)↑ + energy
¤If we heat this reaction, which direction will
the equilibrium favor?
Activation energy - EA
Activation energy - EA
¤Particles must collide to react
¤EA = amount of energy particles need
¤Different for each rxn
Speed of Reaction
¤How can you measure the rate of a
reaction?
¤Reactant disappearing
¤Product forming
¤At Eq. the --> and <-- reactions
occur at the same rate.
Speed of Reaction
¤When is rate important to you?
¤food spoiling
¤hair dye
¤digestion
Factors that effect rate
¤1. Temperature
¤Why does a higher temperate
increase the rate of reactions?
Factors that effect rate
¤2. Surface area
¤Why would the
chopped potatoes
cook faster?
¤Which has a larger
surface area?
Factors that effect rate
¤3. Concentration
¤Solutions: number of particles dissolved
¤Increasing Pressure increases
concentration - FOR GASES only
Catalysts
¤Increase rate of rxn.
¤Do not react
¤Do not MAKE reactions occur; just
make them faster
Catalysts
¤Lowers activation energy
¤“lowering goalpost”
¤i.e. Enzymes
¤“ase” ending
¤Protease break down proteins
Slowing down reactions
¤Inhibitors – don’t STOP reactions,
just slow them down
¤What kind of reactions would you
want to slow down?
Summary
¤Wine & hydrogen peroxide (H2O2) are
often stored in dark glass bottles and at
cool temperatures.
¤Why do you think this is the case? Think
about this in the context of today’s notes.
Word Equations
Zn + Pb(NO3)2 --> Zn(NO3)2 + Pb
AlBr3 + Cl2 --> AlCl3 + Br2
Na3PO4 + CaCl2 --> Ca3(PO4)2 +
NaCl
KClO3 --> KCl + O2
Al + HCl --> H2 + AlCl3
Ca(OH)2 + H3PO4 --> Ca3(PO4)2 +
H 2O
Cu + H2SO4 --> CuSO4 + H2O + SO2
answer key
1. 2 KOH + H2SO4 ➡ K2SO4 + 2 H2O
2. FeS + 2 HCl ➡ FeCl2 + H2S
3. CuSO4 + H2S ➡ CuS + H2SO4
4. 2AgNO3 + H2S ➡ Ag2S + 2HNO3
answer key
5. 2 NaNO3 + H2SO4 ➡ Na2SO4 + 2HNO3
6. KCl + NaNO3 ➡ KNO3 + NaCl
7. H2SO4 + BaCl2 ➡ BaSO4 + 2HCl
8. H2SO4 + 2 NaOH ➡ Na2SO4 + 2 H2O
9. 4Al + 3O2 ➡ 2Al2O3