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Chemistry Unit 2
Chemistry Unit 2
Wear your safety goggles!
Structure of an Atom
Protons and an Atoms identity
Valence Electrons and
Reactivity
The Periodic Table
Chemical Formulas
Chemical Reactions
Chemical Equations
Law of Conservation
of Mass
C h e m i s t r y U n i t 1
C h e m i s t r y U n i t 2
Chemistry Vocabulary, Unit 2, part 1
• pure substance: matter that has the same chemical composition throughout • compound: a substance that forms when two or more elements join chemically • molecule: a group of two or more atoms held together by chemical bonds • chemical formula: a group of chemical symbols and numbers that shows the
kinds and numbers of atoms in a molecule
Chemistry Vocabulary, Unit 2, part 2
physical change: a change in the form or appearance of a substance without a change in the identity of the substance
chemical reaction: a process in which chemicals react, or change, to form new types of matter
precipitate: a solid that forms during a chemical reaction in a solution
reactant: a substance that enters into a chemical reaction
product: a substance that forms during a chemical reaction
combustion reaction: a chemical reaction that occurs when oxygen combines with certain other substances to release heat
rusting: a slow chemical reaction between oxygen and a metalchemical reaction: a process in which chemicals react, or change, to form new types of matter
reactants: the chemicals that enter into a chemical reaction; also called reagents
products: the chemicals that form during a chemical reaction
chemical equation: a statement that shows the reactants and products of a chemical reaction
law of conservation of mass: the principle that states that in any chemical reaction, the amount of matter in the reactants must equal the amount of matter in the products
coefficient: in a chemical equation, a number placed in front of a reactant or product that tells how many molecules of that substance participate in the reaction
physical change: a change in the form or appearance of a substance without a change in the identity of the substance
chemical reaction: a process in which chemicals react, or change, to form new types of matter
precipitate: a solid that forms during a chemical reaction in a solution
reactant: a substance that enters into a chemical reaction
product: a substance that forms during a chemical reaction
combustion reaction: a chemical reaction that occurs when oxygen combines with certain other substances to release heat
rusting: a slow chemical reaction between oxygen and a metalchemical reaction: a process in which chemicals react, or change, to form new types of matter
reactants: the chemicals that enter into a chemical reaction; also called reagents
products: the chemicals that form during a chemical reaction
chemical equation: a statement that shows the reactants and products of a chemical reaction
law of conservation of mass: the principle that states that in any chemical reaction, the amount of matter in the reactants must equal the amount of matter in the products
coefficient: in a chemical equation, a number placed in front of a reactant or product that tells how many molecules of that substance participate in the reaction
Chemistry Vocabulary, Unit 2, part 2
Chemical FormulasSubscripts
And Lettering
carbon dioxide
Pb(OH)4
CO2
Chemical Formulas of Household
Items
Common Name Chemical Name Chemical Formula
aluminum foil aluminum Alvitamin C ascorbic acid C6 H8 O6
vinegar acetic acid (diluted) CH3 COOH
table salt sodium chloride NaCl
road salt calcium chloride CaCl2
table sugar sucrose C12 H22 O11
baking soda sodium bicarbonate NaHCO3
wood alcohol (solvent) methanol CH3 OH
hydrogen peroxide hydrogen peroxide (diluted) H2 O2
dry ice carbon dioxide CO2
nail polish remover acetone CH3 COCH3
chalk, some antacidscalcium carbonate CaCO3
lighter fluid butane C4 H10
tincture of iodine iodine I2
soda water carbonic acid (diluted) H2 CO3
Molecules
Chemical Formula
CaC03
NaCl
C8H10N4O2 Mg3Al2Si3O12
O3 C6 H12 O6
Common Name
calcite
Atoms Present
1 Calcium1 Carbon3 Oxygen
Chemical Formula
CaC03
NaCl
C8H10N4O2 Mg3Al2Si3O12
O3 C6 H12 O6
Common Name
calcite
Atoms Present
1 Calcium1 Carbon3 Oxygen
Chemical Formula
CaC03
NaCl
C8H10N4O2 Mg3Al2Si3O12
O3 C6 H12 O6
Common Name
calcite
Atoms Present
1 Calcium1 Carbon3 Oxygen
A balanced chemical equation shows how a reaction agrees with the law of conservation of mass. Every atom has a specific mass, and that mass cannot be increased or decreased by a chemical reaction. So, if four oxygen atoms enter a chemical reaction, then four oxygen atoms must leave the reaction as well.
• If no coefficient is visible in front of a reactant or product, the coefficient of that reactant or product is 1.
• You might not need to change every coefficient when balancing a chemical equation.
• A coefficient in front of a reactant or product affects each element inside that reactant or product. For example, putting a coefficient of 2 in front of H 2 O means that there are four hydrogen atoms and two oxygen atoms.
• Begin by balancing the element that appears in the fewest places in the equation.
When you balance an equation, remember the following:
Pizza Reactants and Products
Balancing Chemical Reactions
• Unbalanced Reaction– CH4 + O2 CO2 + H2 O
• Balanced Reaction– CH4 + 2 O2 CO2 + 2 H2 O
When you balance an equation, remember the following:
When you balance an equation, remember the following:
• If no coefficient is visible in front of a reactant or product, the coefficient of that reactant or product is 1.
• You might not need to change every coefficient when balancing a chemical equation.
• A coefficient in front of a reactant or product affects each element inside that reactant or product. For example, putting a coefficient of 2 in front of H 2 O means that there are four hydrogen atoms and two oxygen atoms.
• Begin by balancing the element that appears in the fewest places in the equation.
Balancing Chemical Reactions
Balancing Chemical Equations
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Reaction Types
• Physical Reaction
• Chemical Reaction
Types of Reactions Types of Reactions Types of Reactions
Types of ReactionsTypes of ReactionsTypes of Reactions
C25H52 + 38 O2 → 25 CO2 + 26 H2O1. What are the reactants in the chemical reaction that occurs when a candle burns?
2. The products of the reaction are carbon dioxide and water vapor. What two types of energy are also released?
3. What happened when your teacher placed a glass jar over the burning candle? Why do you think this happened?
4. Explain How do you know this is a combustion reaction?
5. Apply How do you know this is a chemical reaction and not just a physical change?
Combustion Reaction C25H52 + 38 O2 → 25 CO2 + 26 H2O
1. What are the reactants in the chemical reaction that occurs when a candle burns?
2. The products of the reaction are carbon dioxide and water vapor. What two types of energy are also released?
3. What happened when your teacher placed a glass jar over the burning candle? Why do you think this happened?
4. Explain How do you know this is a combustion reaction?
5. Apply How do you know this is a chemical reaction and not just a physical change?
Combustion Reaction
8.5 E Questions
• What is a chemical reaction? • What is the difference between a physical
change and a chemical reaction? • How can you tell that a chemical reaction has
taken place? • Are the products of a chemical reaction the
same as the reactants? Explain why or why not. • What types of chemical reactions are there?
8.5 E Key Concepts• A physical change alters the form or appearance of a substance without changing the identity of the substance.
During a physical change, no changes occur in the elements or compounds that make up the matter. For example, when water boils, water vapor is released. The water changes from a liquid to a gas, but it is still water.
A chemical reaction is a process in which elements and compounds combine in new ways to form new substances
Usually a physical reaction can be easily reversed. For example, to change water vapor back into a liquid, you simply let it cool down. A chemical reaction, on the other hand, is not easily reversed.
Some signs that indicate a chemical reaction has occurred include a change in color and the release of heat or light. Sometimes a precipitate forms. A precipitate is a solid that forms during a chemical reaction that takes place in a solution.
• Some chemical reactions cause release of a gas. If you drop an antacid tablet into water, a chemical reaction occurs. The bubbles that you see in the water are carbon dioxide given off by a reaction between a compound in the tablet and the water. But release of gas does not always mean a chemical reaction has taken place. For example, when water boils, this change from liquid water to water vapor is a physical change, not a chemical change.
• The reactants are the chemicals that enter into a chemical reaction. The products are the chemicals that form during a chemical reaction. For example, when acetic acid (vinegar) combines with sodium bicarbonate (baking soda), acetic acid and sodium bicarbonate are the reactants. The products are a salt, water, and a gas—carbon dioxide.
• A combustion reaction is a chemical reaction that occurs when oxygen combines with certain other substances to release heat. A combustion reaction takes place when something burns. When wood burns, water vapor and carbon dioxide are given off. The ash that remains is very different from the wood that burned. It is a new substance with different properties.
Rusting is another example of a chemical reaction. Rusting is a slow reaction between oxygen and a metal. A nail contains iron. Over time, the iron combines with oxygen in the air to form rust. The surface of the nail changes from smooth and shiny to rough and reddish brown. The rust is a different substance from iron.
Evidence of a Chemical Reaction
Precipitation Gas Bubbles Change in color or
temperature
N2 + H2 → NH3
Types of Chemical Reactions
OxidizingCombustion
8.5 F Questions• Why are coefficients included in a chemical equation?• What is the law of conservation of mass? How does it apply
to a chemical reaction?• If 12 oxygen atoms enter a chemical reaction, must the same
12 oxygen atoms be included in the products of the reaction? How do you know?
• How can you tell if a chemical equation is balanced or unbalanced?
• When balancing a chemical equation, which element should you balance first?
8.5 F Key Concepts• A chemical equation shows the reactants and products of a chemical reaction. The reactants are shown on the left side of the equation, and the products are shown on the
right side.
Here is an example of a chemical equation: CH4 + O2 CO2 + H2 O• This equation shows that methane (CH4) and oxygen (O2) react to form carbon dioxide (CO2) and water (H2 O).
The equation above is an unbalanced equation, which means that the numbers of atoms on the left and right sides of the arrow do not match. The equation shows two oxygen atoms in the reactants (on the left side), and three oxygen atoms in the products (on the right side). Also, there are four hydrogen atoms in the reactants and only two hydrogen atoms in the products.
The balanced form of the chemical equation shown above is as follows:
CH4 + 2 O2 → CO2 + 2 H2 O
Placing a coefficient of 2 in front of H2 O makes four hydrogen atoms on both sides of the equation. Then, placing a coefficient of 2 in front of O 2 makes four oxygen atoms on both sides of the equation.
• A balanced chemical equation shows how a reaction agrees with the law of conservation of mass. Every atom has a specific mass, and that mass cannot be increased or decreased by a chemical reaction. So, if four oxygen atoms enter a chemical reaction, then four oxygen atoms must leave the reaction as well.
• In balanced chemical equations, the coefficients show the ratios in which chemicals combine and form. In the reaction between methane and oxygen described above, the ratio of the reactants is 1:2—one methane molecule to two oxygen molecules. This shows that 10 methane molecules will combine with 20 oxygen molecules, or that 1,000 methane molecules will combine with 2,000 oxygen molecules.
• When you balance an equation, remember the following: – If no coefficient is visible in front of a reactant or product, the coefficient of that reactant or product is 1. – You might not need to change every coefficient when balancing a chemical equation. – A coefficient in front of a reactant or product affects each element inside that reactant or product. For example, putting a coefficient of 2 in front of H 2 O means that
there are four hydrogen atoms and two oxygen atoms. – Begin by balancing the element that appears in the fewest places in the equation.
Do Now!!
CaCO3 + HCl --> CaCl2 + H2O+CO2
Examine the chemical equation below and answer the following questions?
1. Is this equation balanced? If not write the balanced equation.
2. What are the reactants?3. What are the products?4. What is the evidence of this reaction?
Teks for Unit 1 and 2• (5) Matter and energy. The student knows that matter is composed of atoms and has chemical and
physical properties. The student is expected to:
• Unit 1• (A) describe the structure of atoms, including the masses, electrical charges, and locations, of protons
and neutrons in the nucleus and electrons in the electron cloud;• (B) identify that protons determine an element's identity and valence electrons determine its
chemical properties, including reactivity; • (C) interpret the arrangement of the Periodic Table, including groups and periods, to explain how
properties are used to classify elements;
• Unit 2• (D) recognize that chemical formulas are used to identify substances and determine the number of
atoms of each element in chemical formulas containing subscripts;• (E) investigate how evidence of chemical reactions indicate that new substances with different
properties are formed; and• (F) recognize whether a chemical equation containing coefficients is balanced or not and how that
relates to the law of conservation of mass.
8.5 D Questions
• The chemical formula for water is H2O. What do the H and O represent? What does the subscript 2 mean?
• The chemical formula for hydrogen peroxide is H2O2. What does the chemical formula tell you about the hydrogen peroxide molecule?
• Is CO the same as CO2? Explain. • One calcium (Ca) atom combines with two chlorine (Cl) atoms
to make calcium chloride. What is the chemical formula of calcium chloride?
• Suppose that all you know about a molecule is its chemical formula. What can the chemical formula tell you?
8.5 D Key Concepts
• An element is made up of only one type of atom. Hydrogen, helium, and oxygen are examples of elements. Elements are pure substances. A pure substance is matter that has the same chemical composition throughout and cannot be separated into its parts by physical means.
Elements form compounds. A compound is a pure substance that forms when two or more elements join chemically in a fixed proportion.
• Just as an element is made up of one kind of atom, a compound is made up of one kind of molecule. A molecule is a group of two or more atoms held together by very strong chemical bonds. These bonds form between atoms that share or transfer electrons. A molecule is the smallest unit of a compound that has all the properties of that compound.
• A molecule can be made up of more than one atom of the same element. For example, two atoms of oxygen join to form a molecule of oxygen gas.
• A molecule can also be made up of two or more different elements. A water molecule is made up of two hydrogen atoms and one oxygen atom. The illustration below is a model of a water molecule.
• Molecules are identified by chemical formulas. A chemical formula is a group of chemical symbols and numbers that shows the kinds and numbers of atoms in a molecule.
• The formula for a water molecule is H2 O. H is the chemical symbol for hydrogen. O is the chemical symbol for oxygen. The number 2 in the formula is called a subscript. It shows that the molecule contains two atoms of hydrogen. The O has no subscript. That means that the molecule contains only one atom of oxygen.
