Download Chemical Reactions and Equations

Today-- Welcome Back!
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Turn in “Chapter 6 Extra Credit”
Unexpected Changes Lab
Introduce Chapter 9 (LAST CHAPTER)
Outlining – NOPE!
Chapter 9 – Chemical
Reactions and Equations
Learning Objectives:
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Be able to balance chemical equations by
applying the law of conservation of mass.
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Be able to recognize synthesis,
decomposition, single replacement,
double replacement, combustion and
neutralization reactions.
Law of Conservation of Matter
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Conservation of Matter: in all chemical and
physical changes, matter is neither created or
destroyed
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The total mass in a chemical reaction remains constant
Antoine Lavoisier:
■ Made accurate and precise measurements
during chemical reactions
Reactants ―› Products
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Reactants:
the substances that enter
into the reaction
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Products:
the substances that are
produced by the reaction
Why Do Reactions Occur
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Think back to what we know about atoms
and specifically their electrons?
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Through chemical reactions, atoms have
the opportunity to obtain complete sets of
valence electrons and thus become more
stable.
Five General Types of
Chemical Reactions
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• Direct Combination (Synthesis)
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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 Equations
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A method of describing chemical reactions
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Word Equations
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Calcium + Oxygen ―› Calcium Oxide
Formula Equations
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2Ca + O2 ―› 2 CaO
the arrow → separates the reactants from the products
Completing the Chemical Equation
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Complete the chemical equation by
describing the physical state of each
substance:
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Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq)
means dissolved in water
Symbols used in equations
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Double arrow
reaction
∆
reaction
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Pt
indicates a reversible
shows that heat is supplied to the
is used to indicate a catalyst is
supplied, in this case, platinum.
What is a catalyst?
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A substance that speeds up a
reaction, without being changed or
used up by the reaction.
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Enzymes are biological catalysts.
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How can you physically speed up a
reaction?
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
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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
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■ calcium + oxygen yields calcium oxide
2Ca + O2 → 2CaO
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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
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water yields hydrogen and oxygen
2H2O
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2H2
+
O2
marble (calcium carbonate) yields calcium
oxide and carbon dioxide
CaCO3
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→
→
CaO
+
CO2
Notice: all equations show a single reactant
decomposing into two (or more) products.
http://www.ric.edu/ptiskus/reactions/Index.htm
Balancing Chemical Equations
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The Law of Conservation of Matter states
that:
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Matter is neither created nor destroyed!
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For mass to remain constant both before and
after a reaction, the number of atoms must
remain constant
Step 1: Balancing Equations
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Write the word equation that describes the
reaction.
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
atoms 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 + O2 ―› CO2 +
H2O
Never
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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
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Never put a coefficient in the middle of a
formula
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2 NaCl is okay, Na2Cl is not.
Balancing Equations:
Examples
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H2
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Co +
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+
O2 →
O2 →
Co2O3
Pb(NO3)2 + K2S →
C2H6
+ O2 →
H2O
PbS +
H2O + CO2
KNO3
Balance the following
iron(II) chloride + sodium phosphate →
sodium chloride + iron (II) phosphate
FeCl2 + Na3PO4 → NaCl +
Fe3(PO4)2
Today
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Look at Single-Replacement Reactions.
Begin “Single-Replacement Lab” set-up.
Single-Replacement Reactions
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Copper metal and silver nitrate:
Cu(s) + AgNO3(aq) → Ag(s) + CuNO3(aq)
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What do you observe about the reaction?
What do you notice about the chemical
equation?
Cu must be more reactive than Ag in order
for the reaction to take place.
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 Lab
Today you will do the following:
1. Formulate a question for the lab
2. Formulate a hypothesis
3. Design procedures
4. Create a data table.
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
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This is the only type of chemical
reaction with two compounds as
reactants and two compounds as
products.
Double Replacement Examples
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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
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This is the only type of chemical
reaction with two compounds as
reactants and two compounds as
products.
Double Replacement Examples
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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
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Reactants must be dissolved in water
(releasing the ions).
Will occur if one of the products :
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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)
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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
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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
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Nitric acid reacts with solid sodium
carbonate to form liquid water and
carbon dioxide gas and sodium nitrate.