Download Chapter 17 – Chemical Change

Chapter 17 – Chemical
Change
17.2 – Balancing Equations
pp. 388-397
17.2 Balancing Equations
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Antoine Laurent Lavoisier, established an
important principal based on his experiments
with chemical reactions.
He stated that the total mass of the products of
a reaction is equal to the total mass of the
reactants.
The law of conservation of mass holds true for
even a burning mass of wood.
17.2 Balancing Equations
17.2 Balancing Equations
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The combined mass of the burning wood
and oxygen is converted into carbon dioxide
and water.
17.2 Conservation of mass
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Lavoisier showed that a
closed system must be
used when studying
chemical reactions.
When chemicals are
reacted in a closed
container, you can
show that the mass
before and after the
reaction is the same.
17.2 Formula mass
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The sum of the atomic mass values of the
atoms in a chemical formula is called the
formula mass.
17.2 Avogadro’s Number
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The Avogadro number was named in honor of
Amedeo Avogadro who discovered that a mole of
any gas under the same conditions has the same
number of molecules.
Johann Josef Loschmidt, a German physicist,
named and discovered the Avogadro number.
Loschmidt realized that a mole of any
substance—be it a gas, liquid, or solid—contains
6.02 x 1023 atoms or molecules.
17.2 Molar Mass
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The mass (in grams) of one mole of a
compound is called its molar mass.
Solving Problems
What is the molar mass of one mole of
CaCO3?
1.
Looking for:
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… molar mass of CaCO3
Given
2.
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… chemical formula
Relationships:
3.
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no. amu in formula = molar mass in grams
Solving Problems
4.
Solution
Formula mass CaC03 = 100.09 g
1 mole CaC03 = 100.09 g CaCO3
17.2 Chemical Equations
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When a chemical reaction is written using
chemical formulas and symbols, it is called
a chemical equation.
17.2 Chemical equations
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An arrow is always included between
reactants and products.
It means “to produce” or “to yield.”
to produce
Reactants
Products
“Methane combines with oxygen gas to produce
carbon dioxide gas and water vapor.”
17.2 Numbers in equations
17.2 Balancing equations
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The law conservation of mass is applied by
balancing the number and type of atoms on either
side of the equation.
17.2 Balancing equations
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Counting atoms is necessary to balance
an equation.
How many carbon atoms?
How many hydrogen atoms?
How many oxygen atoms?
17.2 Steps for balancing
If not provided, write the word form of the
equation.
1.
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Calcium carbonate reacts with hydrochloric acid to
produce calcium chloride, carbon dioxide and water.
17.2 Steps for balancing
2.
If not provided, write the chemical
equation from the word form.
17.2 Steps for balancing
3.
Count the number of each type of atom
on both sides.
17.2 Steps for balancing
4.
Add coefficients to balance the equation.
Solving Problems
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In this reaction, chalcocite (a
mineral) reacts with oxygen in the
presence of heat. The products are
a type of copper oxide and sulfur
dioxide. Balance this equation:
Cu2S + O2 → Cu2O + SO2
Solving Problems
Looking for:
1.
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…the coefficients for each molecule
Given
2.
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… chemical formulas which show types
and no. of atoms
Solving Problems
Relationships
3.
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Coefficients can be added in front of any
chemical formula in a chemical equation.
When a coefficient is added in front of a
chemical formula, all atoms in that formula
are multiplied by that number.
Use common denominators to help choose
coefficients to try.
Solving Problems
4.
Solution- Trial and error