Reminders
• End of semester Fri. Jan 24th (15 school days)
• Finals Jan 22-24
• Chp 6 E.C.
(Passed out today/ due Mon. Jan 13th)
One cool thing you did over break…
Today
• Chp 9 Learning Targets
• Unexpected Changes Lab
• Introduction to Chp 9
• Handout E.C. assignment
Chapter 9
(Last one for the semester!)
Chemical Reactions and
Writing Equations
1/6/14 Learning Targets
• Describe the characteristics of a chemical
reaction.
• Explain how a chemical equation describes
what happens in a chemical reaction.
Important Terms:
• Chemical Change (Reaction)- a process in
which pure substance(s) are converted into
different pure substance(s)
• Conservation of Matter- in chemical and
physical reactions, matter is neither created
nor destroyed
Examples
Combustion of Ethanol
Oxidation of Iron
Precipitation of Silver
Formation of Coral Reefs (from Calcium Carbonate)
How do we describe/represent what
happens in a chemical reaction?
Reactants- substances which are present before
a chemical reaction
Products- substances which are present after a
chemical reaction
What causes chemical reactions?
• What do we know about the importance of valence
electrons?
Chemical reactions provide atoms the opportunity
to achieve a full set of valence electrons and
become more stable (more energetically favorable)
Since some elements/molecules are already stable,
energy sometimes has to be supplied to initiate a
chemical reaction (think back to the flame test lab)
(strike a match!)
Reminders
• End of semester Jan 24 (14 school days)
• Finals Jan 22-24
1/7/14 Learning Targets
• Explain how a balanced chemical equation
illustrates the law of conservation of matter.
• Understand the five general types of reactions
and how to balance them.
Types of Chemical Reactions
1)
2)
3)
4)
5)
Synthesis
Decomposition
Single Replacement
Double Replacement
Combustion
By knowing the type of reaction that is
occurring, you can predict the products that will
be formed.
Chemical EquationsHow we describe what is happening
Using WordsHydrogen reacts with oxygen to form (or yield)
water
Using Formulas and Symbols
2H2 + O2  2H2O
Breaking down the Notation of
Chemical Equations
2H2(g) + O2(g)  2H2O(l)
Describing the physical state of each
substance
■ Solid
(s)
■ Liquid (l)
■ Gas (g)
■ Aqueous (aq)
means dissolved in water
Coefficient
• Like in math, the coefficient is the number
placed in front of a formula. This number
indicates the quantity of each molecule or
atom in the reaction.
• Ex.
2Ca(s) + O2(g)  2CaO(g)
Symbols used in Chemical Equations
•
Double arrow indicates a reversible reaction
•
Shows that heat is supplied to the reaction
•
Used to indicate a catalyst is supplied, in this case,
platinum.
All of these are special conditions
Balancing Chemical Equations
• Since the conservation of mass says matter is
neither created nor destroyed, we have to
make sure our equation agrees
• # reactant atoms must = # product atoms
Step 1: Balancing Equations
•
Write the word equation that describes the
reaction.
iron reacts with oxygen to yield iron oxide
Or
Iron + Oxygen  Iron Oxide
Step 2: Balancing Equations
2. Replace
the words in the equation with
symbols and formulas.
Fe
+ O2

Fe2O3
Do we have the same numbers of each
element on both sides of arrow?
Does this follow the law of conservation of
matter?
Step 3: Balancing Equations
3. Count
the # of atoms of each element
on both sides of the equation.
Fe
+ O2

Fe2O3
Step 4: Balancing Equations
4.
Starting with elements that only occur
in one substance on each side of the
equation, make sure that each side of the
equation has an equal # of that element.
Proceed with all elements.
Remember that changing the # of one element
may alter elements that have already been
balanced.
Fe
+ O2
―›
Fe2O3
Let’s try:
CH4 +2O2  CO2 + 2H2O
!
•
Never change a subscript to balance an
equation.
If you change the formula you are describing a
different reaction.
■ H2O is a different compound than H2O2
■
•
Never put a coefficient in the middle of a
formula
■
2 NaCl is okay, Na2Cl is not.
Step 5: Check Your Work
5. Make
sure that the equation is properly
balanced.
CH4 + 2O2  CO2 + 2H2O
Balancing Equations:
Examples
■
H2
■
Co +
■
+
O2 →
O2 →
H2O
Co2O3
Pb(NO3)2 + K2S →
PbS +
KNO3
Balance the following
iron(II) chloride + sodium phosphate →
sodium chloride + iron (II) phosphate
FeCl2 + Na3PO4 → NaCl +
Fe3(PO4)2
Today
■
■
Look at 3 different types of reactions.
Begin “Single-Replacement Lab” set-up.
Five General Types of
Chemical Reactions
•
• Direct Combination (Synthesis)
•
•
•
•
Decomposition
Single-Replacement
Double-Replacement
Combustion
By knowing the type of reaction that is
occurring, you can predict the products that
will be formed.
I. Direct Combination Reactions
(also called synthesis reactions).
General form: A + B → AB
(two reactants make a single product)
A, B = elements or compounds
AB = compound consisting of A and B
■
This is the only type of chemical reaction in
which there is a single product formed.
This single product is always more complex
than the reactants.
Examples of Synthesis Reactions
■
■ calcium + oxygen yields calcium oxide
2Ca + O2 → 2CaO
■
carbon dioxide + water yields carbonic acid
CO2
■
■
+
H2O
→
H2CO3
Notice: All equations show two (or more)
reactants, but only one product.
http://www.ric.edu/ptiskus/reactions/Index.htm
II. Decomposition Reactions
General form: AB → A + B
(one reactant makes two or more products)
AB = compound
A, B = elements or simpler compounds
▪ This is the only type of chemical reaction in
which there is a single reactant. This single
reactant is always more complex than the
products.
Decomposition Reactions:
Examples
■
water yields hydrogen and oxygen
2H2O
■
■
2H2
+
O2
marble (calcium carbonate) yields calcium
oxide and carbon dioxide
CaCO3
■
→
→
CaO
+
CO2
Notice: all equations show a single reactant
decomposing into two (or more) products.
http://www.ric.edu/ptiskus/reactions/Index.htm
III. Single-Replacement Reactions
General Form: A + BX → AX + B
One element and one compound recombine
(switch partners)
AX, BX = ionic compounds
A, B = Metals
X = ion that switches partners
*Metal ‘A’ must be more reactive than
‘B’ for this to occur
Single-Replacement Examples
■
Copper metal and silver nitrate:
Cu + AgNO3 → CuNO3 + Ag
■
Notice: In the reaction, an copper
combines with silver nitrate to
create copper nitrate and silver
■
Zn + HCl → ZnCl2 + H2
IV. Double-Replacement
Reactions
General form: AX + BY → AY + BX
(Positive ions in two compounds are exchanged)
A,B = positive ions
X,Y = negative ions
■
This is the only type of chemical
reaction with two compounds as
reactants and two compounds as
products.
Double Replacement Examples
■
calcium carbonate and hydrochloric acid yield
calcium chloride and carbonic acid
CaCO3 + 2HCl → CaCl2 + H2CO3
■ Notice: in this reaction, two ionic compounds
exchange ions to form two new ionic
compounds
www.ric.edu/ptiskus/reactions/Index.htm
IV. Double-Replacement
Reactions
General form: AX + BY → AY + BX
(Positive ions in two compounds are exchanged)
A,B = positive ions
X,Y = negative ions
■
This is the only type of chemical
reaction with two compounds as
reactants and two compounds as
products.
Double Replacement Examples
■
calcium carbonate and hydrochloric acid yield
calcium chloride and carbonic acid
CaCO3 + 2HCl → CaCl2 + H2CO3
■ Notice: in this reaction, two ionic compounds
exchange ions to form two new ionic
compounds
www.ric.edu/ptiskus/reactions/Index.htm
Rules of Double-Replacement
Reactions
■
■
Reactants must be dissolved in water
(releasing the ions).
Will occur if one of the products :
•
•
•
is a molecule (covalent),
a precipitate (solid comes out of solution),
or
an insoluble gas.
V. Combustion Reactions
General Form:
CxHy + O2 → H2O + CO2
(hydrocarbon and oxygen react to form
carbon dioxide and water)
■
This is the only type of chemical
reaction where something reacts with
oxygen and forms carbon dioxide and
water
Combustion Examples
▪ Methane reacts with oxygen:
CH4 (methane) + O2 → H2O + CO2
▪ Gasohol reacts with oxygen:
C2H5OH (ethanol) + O2 → H2O + CO2
▪ Notice: in both cases, water and carbon dioxide are
the products.
www.ric.edu/ptiskus/reactions/Index.htm
1. Write the word equation
2. Write the balanced formula
equation
■
Solid iron (III) sulfide reacts with
gaseous hydrogen chloride to form iron
(III) chloride and hydrogen sulfide gas.
1. Write the word equation
2. Write the balanced formula
equation
■
Nitric acid reacts with solid sodium
carbonate to form liquid water and
carbon dioxide gas and sodium nitrate.