chapter 17 – chemical change 17.2 – balancing equations pp. 388-397
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Chapter 17 – Chemical Change
17.2 – Balancing Equationspp. 388-397
17.2 Balancing Equations
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
The combined mass of the burning wood and oxygen is converted into carbon dioxide and water.
17.2 Conservation of mass 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
The sum of the atomic mass values of the atoms in a chemical formula is called the formula mass.
17.2 Avogadro’s Number 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
The mass (in grams) of one mole of a compound is called its molar mass.
What is the molar mass of one mole of CaCO3?
1. Looking for: … molar mass of CaCO3
2. Given … chemical formula
3. Relationships: no. amu in formula = molar mass in
grams
Solving Problems
4. Solution
Solving Problems
Formula mass CaC03 = 100.09 g
1 mole CaC03 = 100.09 g CaCO3
17.2 Chemical Equations When a chemical reaction is written
using chemical formulas and symbols, it is called a chemical equation.
17.2 Chemical equations
An arrow is always included between reactants and products.
It means “to produce” or “to yield.”
Reactants Products
to produce
“Methane combines with oxygen gas to produce carbon dioxide gas and water vapor.”
17.2 Numbers in equations
17.2 Balancing equations 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 Counting atoms is necessary to
balance an equation.
How many hydrogen atoms?
How many oxygen atoms?
How many carbon atoms?
17.2 Steps for balancing
1. If not provided, write the word form of the equation.
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 balancing3. Count the number of each type of
atom on both sides.
17.2 Steps for balancing4. Add coefficients to balance the
equation.
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
1. Looking for: …the coefficients for each molecule
2. Given … chemical formulas which show
types and no. of atoms
Solving Problems
3. Relationships 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
Solving Problems
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