Do Now – April [2(10) + 3], 2009

1. Did you share your love for the Earth with anyone after school yesterday? If so, how?

2. What is a chemical reaction?

Agenda

• Do Now/Announcements

• How to represent chemical reactions

• Types of chemical equations

• Start balancing chemical equations

• Work time

• Exit Ticket

Objectives

• SWBAT write skeleton equations from word equations.

• SWBAT balance skeleton (chemical) equations.

Remember Chemical Reactions?

What is a chemical reaction?

A chemical reaction is a process by which

atoms of one or more substances are

rearranged to form different substances

What is a chemical equation?

• A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction

Chemical Equations are like Cookbook Recipes

• A chemical equation is similar to a cookbook recipe in that it shows how many units of each substance is required to give the desired result

• It shows the combination of various elements and/or molecules and then the resulting elements and/or molecules

Chemical Equations or…Math?

• Chemical equations are similar to algebraic equations in that the total number of atoms of each element on the left side must equal the number for that element on the right side

A mathematical equation: x+2x=3x

A chemical equation:

C3H8 + 5 O2 3 CO2 + 4 H20

Parts of a Chemical Equation

A chemical equation identifies the starting and finishing chemicals as reactants and

products:

reactants products

Example (combustion of propane)

C3H8 + 5 O2 3 CO2 + 4 H20

3 Types of Chemical Equations

Word equations

Skeleton equations

Balanced equations

Solids, Liquids, Gases…and One More

• The reactants and products can exist in 4 different forms (or phases)

Solid (s)

Liquid (l)

Gas (g)

In water/Aqueous (aq)

Word Equations

• Word equations use words to show chemical reactions

Example:

Solid iron and chlorine gas react to form solid iron(III) chloride

iron (s) + chlorine (g) iron(III) chloride (s)

• It’s like a short “chemical sentence” describing a chemical reaction!

Word Equations - Practice

• Write the word equation for the following…

1.Solid magnesium and chlorine gas react to form solid magnesium chloride

2.The reaction of hydrogen gas and bromine gas yields hydrogen bromide gas

3.Aqueous sodium hydroxide reacts with aqueous hydrogen chloride to produce solid sodium chloride and aqueous dihydrogen monoxide.

Skeleton Equations• Skeleton equations use chemical

formulas rather than words to identify products and reactants

Example:Word: iron (s) + chlorine (g) --> iron(III)

chloride (s) Think: What are the formulas for each part

of the reaction?

Iron = Fe, Chlorine gas = Cl2Skeleton: Fe (s) + Cl2 (g) --> FeCl3 (s)

Skeleton Equations - Practice

• Write the skeleton equations for the following…

1.hydrogen (g) + bromine (g) --> hydrogen bromide (g)

2.carbon monoxide (g) + oxygen (g) --> carbon dioxide (g)

3.potassium chlorate (s) --> potassium chloride (s) + oxygen (g)

Chlorate is a polyatomic ion: (ClO3)-1

How molecules are symbolizedCl2 2 Cl 2 Cl2

• Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH)2

O H

O H

Ca• Notice that the OH is a group• The 2 refers to both H and O

Chemical Equations and the Law of Conservation of Matter

• Chemical equations shows how the law of conservation of matter is obeyed

• The mass of atoms of REACTANTS must equal the mass of atoms of PRODUCTS

• When Massreactants = Massproducts you have a balanced chemical equation

Balanced Chemical EquationsFe (s) + Cl2 (g) --> FeCl3 (s)

NOT BALANCED!

To balance an equation, you must determine the correct coefficient for chemical formulas in

skeleton equation. A coefficient is a number in front of a reactant or product.

Balanced Chemical Equations Fe (s) + Cl2 (g) --> FeCl3 (s)

COEFFICIENTS

NOT BALANCED!

Fe (s) + Cl2 (g) --> FeCl3 (s)

BALANCED: 2 Fe and 6 Cl on each side!

2 3 2

Determine whether the following equations are balanced

Are there the same number of atoms of each element on both sides of reaction?

1. 2 Al + HCl --> 3 AlCl3 + 3H2

2. Ba(ClO3)2 --> BaCl2 + 2O2

3. 3 Sn(SO4)2 + 4 K3PO4 --> Sn3(PO4)4 + 6 K2SO4

4. C5H12 + 11 O2 --> 5 CO2 + 12 H2O

TIP!

Keep track of each element when counting the number of electrons!

Rules of Balancing

• RULES: You cannot change the subscript! You cannot put a coefficient in the middle of a formula!

Reaction to Yield WaterUnbalanced reaction:

H2 + O2 H2O

Correct, balanced equation:

2 H2 + O2 2 H2O

Balanced equation, but coefficients not whole numbers: H2 + ½ O2 H20

Balanced, but its coefficients are not least whole numbers:4 H2 + 2 O2 4 H20

Balance equations by “inspection”

Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity.

5

4 67

2 222 63

a) P4 + O2 P4O10

b) Li + H2O H2 + LiOHc) Bi(NO3)3 + K2S Bi2S3 + KNO3

d) C2H6 + O2 CO2 + H2O

Mg + O2 MgO 2Mg + O2 2MgO is correctMg + ½O2 MgO is incorrectMg2+ O2 2MgO is incorrect

4Mg + 2 O2 4MgO is incorrect

a) Mg + HCl MgCl2 + H2

b) Ca + N2 Ca3N2

c) NH4NO3 N2O + H2O

d) BiCl3 + H2S Bi2S3 + HCl

e) C4H10 + O2 CO2 + H2O

f) O2 + C6H12O6 CO2 + H2O

g) NO2 + H2O HNO3 + NO

h) Cr2(SO4)3+ NaOH Cr(OH)3+ Na2SO4

Balance these skeleton equations:

a) Mg + 2HCl MgCl2 + H2

b) 3Ca + N2 Ca3N2

c) NH4NO3 N2O + 2H2O

d) 2BiCl3 + 3H2S Bi2S3 + 6HCl

e) 2C4H10 + 13O2 8CO2 + 10H2O

f) 6O2 + C6H12O6 6CO2 + 6H2O

g) 3NO2 + H2O 2HNO3 + NO

h) Cr2(SO4)3+ 6NaOH 2Cr(OH)3+

3Na2SO4

Balance these skeleton equations:

Exit Ticket

Balance the following chemical equation:

Al4C3 + H2O CH4 + Al(OH)3