chemical change. chapter seventeen: chemical change 17.1 chemical reactions 17.2 balancing...
TRANSCRIPT
CHEMICAL CHANGE
Chapter Seventeen: Chemical Change
17.1 Chemical Reactions
17.2 Balancing Equations
17.3 Classifying Reactions
Chapter 17.1 Learning Goals
Describe how energy is involved in chemical changes.
Identify evidence that a chemical change has occurred.
Explain what happens during chemical reactions.
Investigation 17A
Key Question:How are atoms conserved in a chemical
reaction?
Chemical Equations
17.1 Chemical ReactionsA chemical reaction is
the process of breaking of chemical bonds in one or more substances, and the reforming of new bonds to create new substances.
When you make pizza, which changes are physical and which are chemical changes?
17.1 Chemical ReactionsThe process of making pizza involves some
physical changes (like chopping vegetables).
The processes used by yeast in the dough or by the gas stove to bake the pizza are chemical changes.
17.1 Evidence of chemical change
Four indicators of chemical change are:
1. Formation of new gas
2. Formation of new solid
3. Release of energy (heat or light)
4. Color change
17.1 Products and reactants In chemical reactions, you start
with reactants that are combined to make products.
The reactants are the starting substances.
The products are the new substances which result from the chemical reaction.
17.1 Reactants and productsIn the reaction, methane (a natural gas) is burned
or combusted.
Some energy is added to get the reaction started.
17.1 Reaction symbols
The small symbols in the parentheses (s, l, g, aq) next to each chemical formula indicate the phase of each substance in the reaction.
Chapter Seventeen: Chemical Change
17.1 Chemical Reactions
17.2 Balancing Equations
17.3 Classifying Reactions
Chapter 17.2 Learning Goals
Relate a balanced chemical equation to the law of conservation of mass.
Determine the formula and molar masses of chemical compounds.
Write and balance chemical equations.
Investigation 17B
Key Question:How do scientists describe what happens in a
chemical reaction?
Conservation of Mass
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
The combined mass of the burning wood and oxygen is converted into carbon dioxide and water.
17.2 Conservation of massLavoisier 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 NumberThe 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 Use periodic table and round values as
needed.
Solving Problems
Formula mass CaC03 = 100.19 g
1 mole CaC03 = 100.19 g CaCO3
17.2 Chemical EquationsWhen 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 equationsThe 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 Balancing chemical equations
A balanced chemical equation has the same number of each type of atom on the product side and the reactant side.
To balance the equation, we add another water molecule to the product side and add another oxygen molecule to the reactant side.
We can practice balancing equations using CPO periodic table tiles and pencil and paper.
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
Chapter Seventeen: Chemical Change
17.1 Chemical Reactions
17.2 Balancing Equations
17.3 Classifying Reactions
Chapter 17.3 Learning Goals
Classify reactions based on how atoms combine to create new substances.
Discuss applications of polymer science.
Study examples of combustion reactions.
Investigation 17C
Key Question:How can you predict the products of a
chemical reaction?
Classifying Chemical Reactions
17.3 Addition reactionsThe process of creating large molecules from small ones is called polymerization.
17.3 Addition reactionsIn an addition reaction, two or more substances combine to form a new compound.
17.3 Addition reaction
A + B -----> AB
Fe + O2 -----> Fe2O34 3 2
Fe (s) + O2 (g) -----> Fe2O3 (s)
Remember to balance!
17.3 Decomposition reactionsA chemical reaction in which a single
compound is broken down to produce two or more smaller compounds is called a decomposition reaction.
17.3 Decomposition reaction
AB -energy-> A + B
H2O (l)
-electricity-
>
H2 (g) O2 (g)+22
NaHCO3
(s)
-heat-> H2 (g)CO2
(g)
+ 22 +Na2O
(s)
17.3 Single Displacement
In a single-displacement reaction, one element replaces a similar element in a compound.
Cl2 Fe
BX
CuCl2Fe Cu
B AA
17.3 Single Displacement
----->
+ X +
----->
+----->
+ +
17.3 Double DisplacementIn a double-displacement reaction, ions
from two compounds in solution exchange places to produce two new compounds.
One of the compounds formed is usually a precipitate that settles out of the solution, a gas that bubbles out of the solution, or a molecular compound such as water.
17.3 Double Displacement
AB + CD ---> AC + BD
Pb(NO3)2 + KI ---> PbI2 + KNO3
2 2
17.3 Precipitation reactions
A precipitate is a new solid product that comes out of solution in a chemical reaction.
The formation of a cloudy precipitate is evidence that a double-displacement reaction has occurred.
17.3 PrecipitationThe limewater test for carbon dioxide is a precipitation reaction.
17.3 Combustion reactionsA combustion reaction, also called burning, occurs when a substance such as wood, natural gas, or propane combines with oxygen and releases a large amount of energy in the form of light and heat.
17.3 Combustion reactions
What do reactants like wood, natural gas, and propane have in common?
17.3 Combustion
CxHy + O2 ---> CO2 + H2O + energy
C6H12O6 + O2 ---> CO2 + H2O
66 6
+ energy
Hydrogen Powered Cars
Scientists and engineers from government agencies, universities, and all of the major automobile manufacturers are designing, building, and testing hydrogen fuel cell vehicles, also known as FCVs.