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Lesson 1:Chemical Properties and Changes

Lesson 2: Chemical Equations

Lesson 3: Energy and Chemical Change

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chemical property

chemical change

dissolving

8.1 Chemical Properties and Changes

Ability to Change

• In a chemical change, the properties that give a substance its identity change.

8.1 Chemical Properties and Changes

• Properties of matter help identify objects.

• Properties are either physical or chemical.

What properties do elements have?

Ability to Change (cont.)

• A chemical property is the ability or inability of a substance to combine with or change into one or more new substances.

8.1 Chemical Properties and Changes

Chemical Properties

• Examples of chemical properties include burning or rusting.

• Some substances do not react.

8.1 Chemical Properties and Changes

Physical Properties• Physical properties can be observed without

changing the substance.

8.1 Chemical Properties and Changes

Chemical and Physical Changes• Chemical changes change one substance into

another substance.

• Usually chemical changes cannot be easily reversed.

8.1 Chemical Properties and Changes

Property Changes

Forming New Substances• All chemical changes produce substances that are different

from the starting substances.

– A compound is decomposed into its elements.

– Two elements join to form a compound.

8.1 Chemical Properties and Changes

Physical Changes• A physical change is a change in which the properties of a substance

change but the identity of the substance remains the same.

• Dissolving is a process in which substances mix evenly with one another.

8.1 Chemical Properties and Changes

Lesson 1 Review

Which is a chemical change?

A boiling

B burning

C dissolving

D melting

8.1 Chemical Properties and Changes

A B C D

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1. A

2. B

3. C

4. D

Lesson 1 Review

Which is NOT a chemical change?

A sodium metal and chlorine gas react to form salt

B salt dissolving in water

C paper burning

D iron rusting

8.1 Chemical Properties and Changes

A B C D

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1. A

2. B

3. C

4. D

Lesson 1 Review

Which is NOT a physical change?

A melting

B boiling

C dissolving

D burning

8.1 Chemical Properties and Changes

A B C D

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1. A

2. B

3. C

4. D

End of Lesson 1

law of conservation of mass

reactants

products

diatomic molecule

coefficient

8.2 Chemical Equations

Is matter conserved in chemical reactions?

• Chemical equations show that in chemical reactions, atoms rearrange, but no atoms are gained or lost.

8.2 Chemical Equations

Antoine Lavoisier• Lavoisier invented a balance to make more precise

measurements.

• He also determined that the mass before and after a chemical reaction was the same.

8.2 Chemical Equations

Conservation of Mass• The law of conservation of mass states that the total mass before a

chemical reaction is equal to the total mass after the reaction.

8.2 Chemical Equations

Writing a Chemical Equation• Reactants are the starting materials in a chemical reaction and are placed on the

left side.

• Products are the ending materials in a chemical reaction and are placed on the right side.

8.2 Chemical Equations

Word Equations• “Tin + oxygen → tin oxide” reads as “tin plus oxygen

produces tin oxide.”

• Word equations can be long and do not show that mass is conserved.

8.2 Chemical Equations

Elements, Compounds, and Molecules

• Instead of writing long word equations, scientists use symbols and formulas.

– Symbols represent atoms.

– Formulas represent molecules.

– Molecules may be elements or compounds.

8.2 Chemical Equations

Elements, Compounds, and Molecules (cont.)

• Some elements are diatomic, that is, they contain two atoms.

8.2 Chemical Equations

• Molecules may also contain two different elements, such as hydrogen and oxygen in a water molecule.

Elements, Compounds, and Molecules (cont.)

8.2 Chemical Equations

Chemical Equations• Use the symbols and formulas instead

of words.

8.2 Chemical Equations

Balancing a Chemical Equation• Atoms are neither gained nor lost in a reaction, so both

sides of the equation must have the same number of atoms.

8.2 Chemical Equations

Counting Atoms• A subscript tells how many atoms of

an element are in one molecule.

8.2 Chemical Equations

• A coefficient tells how many atoms, molecules, or formula units are in a reaction.

8.2 Chemical Equations

Comparison of Coefficients and Subscripts

Writing Balanced Equations

Step 1 Determine the correct symbols and formulas for reactants and products.

Step 2 Write reactant symbols and formulas to the left of an arrow and product symbols and formulas to the right.

Step 3 Count the number of each kind of atom on both sides.

Step 4 Use coefficients to make the number of each kind of atom the same on both sides of the arrow.

Step 5 Check to see that each kind of atom balances.

8.2 Chemical Equations

Equations for Common Chemical Reactions

Reaction of methane:

CH4 + O2 → CO2 + H2O balance hydrogen

CH4 + O2 → CO2 + 2H2O balance oxygen

CH4 + 2O2 → CO2 + 2H2O

8.2 Chemical Equations

Equations for Common Chemical Reactions (cont.)

Baking soda and vinegar:

NaHCO3 + HC2H3O2 → CO2 + H2O + NaC2H3O2

8.2 Chemical Equations

Using Parentheses with Formulas• When counting atoms inside parentheses, the

subscript multiplies all atoms inside.

Ca + H2O → Ca(OH)2 + H2

Ca + 2H2O → Ca(OH)2 + H2

8.2 Chemical Equations

Lesson 2 Review

Which is a diatomic molecule?

A O2

B H2O

C CH4

D N

8.2 Chemical Equations

A B C D

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1. A

2. B

3. C

4. D

Lesson 2 Review

What is potassium bromide (KBr)?

A an element

B a mixture

C a compound

D a diatomic molecule

8.2 Chemical Equations

A B C D

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1. A

2. B

3. C

4. D

Lesson 2 Review

In the following equation, which is a reactant?

Ca +2H2O → Ca(OH)2 + H2

A H2

B (OH)2

C Ca

D none of the above

8.2 Chemical Equations

A B C D

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1. A

2. B

3. C

4. D

End of Lesson 2

8.3 Energy and Chemical Change

law of conservation of energy

exothermic process

endothermic process

Energy and Chemical Reactions• In chemical reactions, energy is either absorbed or

released.

• In chemical reactions, atoms rearrange.

• Rearrangement involves some form of energy, usually thermal energy.

8.3 Energy and Chemical Change

Light From Chemical Reactions• Some reactions give off light with almost

no thermal energy.

• Cold light occurs at room temperature.

8.3 Energy and Chemical Change

Conservation of Energy

• Energy is stored in reacting molecules.

• The law of conservation of energy states that energy cannot be created or destroyed, simply changed from one form to another.

8.3 Energy and Chemical Change

Chemical Bonds• Molecules have chemical energy stored in their bonds.

• Energy is stored in the food that you eat and transferred to your cells.

8.3 Energy and Chemical Change

Net Release of Energy• When atoms rearrange, bonds are broken and new

bonds form.

– Breaking bonds requires energy.

– Forming bonds releases energy.

8.3 Energy and Chemical Change

Net Release of Energy (cont.)

• An exothermic process releases energy.

• The products in an exothermic reaction have less energy than the reactants.

8.3 Energy and Chemical Change

Net Release of Energy (cont.)

• An endothermic process absorbs energy.

• The products in an endothermic reaction have a higher energy than the reactants.

8.3 Energy and Chemical Change

Lesson 3 Review

Products have a higher energy level than the reactants in an endothermic reaction.

A False

B True

8.3 Energy and Chemical Change

1. A

2. B

Lesson 3 Review

____ bonds ____ energy.

A Breaking; releases

B Breaking; requires

C Forming; requires

D Ionic; release

8.3 Energy and Chemical Change

A B C D

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1. A

2. B

3. C

4. D

Lesson 3 Review

The law of ____ states that energy is neither created nor destroyed in a chemical reaction.

A conservation of mass

B definite proportions

C conservation of matter

D conservation of energy

8.3 Energy and Chemical Change

A B C D

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1. A

2. B

3. C

4. D

End of Lesson 3

Chapter Resources Menu

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Chapter Assessment

California Standards Practice

Image Bank

Science Online

Interactive Table

Virtual Lab

BrainPOP

Which is a chemical change?

A copper turning green from exposure to air

B drying clothes

C ice melting

D none of the above

Chapter Assessment 1

A B C D

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1. A

2. B

3. C

4. D

Which is a chemical property?

A boils at 100°C

B has a volume of 500 ml

C does not rust

D has a luster

Chapter Assessment 2

A B C D

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1. A

2. B

3. C

4. D

Which does NOT describe an exothermic reaction?A There is a net release

of energy.B The reactants have a

higher energy than the products .

C The reactants are lower in energy than the products.

D The products are less stable than the reactants.

Chapter Assessment 3

A B C D

0% 0%0%0%

1. A

2. B

3. C

4. D

What is the coefficient of H2O?

Ca + 2H2O → Ca(OH)2 + H2

A 1

B 0

C 4

D 2

Chapter Assessment 4

A B C D

0% 0%0%0%

1. A

2. B

3. C

4. D

How many (OH) molecules are in the products?

Ca + 2H2O → Ca(OH)2 + H2

A 1

B 2

C 3

D 4

Chapter Assessment 5

A B C D

0% 0%0%0%

1. A

2. B

3. C

4. D

In a chemical reaction, which law states the products have the same mass as the reactants?A Law of Conservation

of WaterB Law of Conservation

of EnergyC Law of Conservation

of MassD Law of Conservation

of Particles

CA Standards Practice 1

SCI 5.b

A B C D

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1. A

2. B

3. C

4. D

Energy is ____ in exothermic reactions.

A absorbed

B created

C released

D stored

CA Standards Practice 2

SCI 5.c

A B C D

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1. A

2. B

3. C

4. D

If an equation is balanced, the number of atoms in the products is ____ the number of atoms in the reactants.

A greater than

B less than

C equal to

D none of the above

CA Standards Practice 3

SCI 3.b

A B C D

0% 0%0%0%

1. A

2. B

3. C

4. D

Which of the following is a physical change?

A hydrogen burning

B iron rusting

C copper turning green when exposed to air

D none of the above

CA Standards Practice 4

SCI X.X

A B C D

0% 0%0%0%

1. A

2. B

3. C

4. D

Symbols represent ____ and ____ represent molecules.

A elements; formulas

B formulas; equations

C molecules; formulas

D elements; equations

CA Standards Practice 5

SCI 3.f

A B C D

0% 0%0%0%

1. A

2. B

3. C

4. D

Image Bank

Interactive Table

Comparison of Coefficients and Subscripts

End of Resources