Balancing Chemical Equations and Types of Chemical Reactions

09.24 & 09.25 2012Boon Chemistry

Catalyst Take out your Homework. Identify the reactants and products in

the following chemical reaction equations:› 2 Mg (s) + O2 (g) 2 MgO (s)

› CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l)

Write the chemical reaction equation for the following description:› Hydrogen gas and oxygen gas combine to form

liquid water.

Catalyst Answers: Take out your Homework. Identify the reactants and products in the

following chemical reaction equations:› 2 Mg (s) + O2 (g) 2 MgO (s)

› CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l)

› Reactants are on the left and products on the right of the arrow.

Write the chemical reaction equation for the following description:› Hydrogen gas and oxygen gas combine to form liquid

water.

› 2 H2 (g) + O2 (g) 2 H2O (l)

Objectives I can compare and contrast different

types of chemical reactions.

I can define and identify a balanced chemical equation.

I can balance simple chemical equations.

Agenda Catalyst (10) Balancing Notes & HW Review (20) Group Work: Balancing Chemical

Equations. (40) Types of Chemical Equations Reading

Activity (40)› Group Work (20)› Presentations & Debrief (20)

Exit Slip (10)

Why do we balance Chemical Reactions?

Law of Conservation of Mass

Matter cannot be created or destroyed in a chemical reaction

The number of atoms on the reactant side must equal the atoms of the products

+H2 H2OO2(g) (g) (l)

H H O O HH O

Unbalanced!

HH OH H

Balanced!

Balanced Chemical Equations A chemical equation is “balanced” when

there are the same number of atoms of each element on both sides of the arrow.

NaHCO3 (s) + HC2H3O2 (aq) èNaC2H3O2 (aq) + CO2 (g) + H2O (l)

Is it balanced?Reactants ProductsNa = 1 Na = 1

H = 5 H = 5

C = 3 C = 3

O = 5 O = 5

Is it balanced? Practice Determine the number of atoms of

each element in the reactants and products. Then, state whether the equation is balanced.

1. P4 + O2 → P2O5

2. C3H8 + O2 → CO2 + H2O

3. Ca2Si + Cl2 → CaCl2 + SiCl44. Si + CO2 → SiC + SiO2

Not balanced.Not balanced.

Not balanced.

Not balanced.

Balancing Equations

Only the coefficients can be changed!

H2 H2O+ O2(g) (g) (l)

H =

O =

H =

O =

2

2

2

1

coefficient

2

4

2

2

4

Balancing Tips

Always balance non-Oxygen’s & Hydrogen’s first (ex. Chlorine)

Then balance Hydrogens Balance Oxygens Last

Balancing Practice!1. P4 + O2 → P2O5

P4 + 5 O2 → 2 P2O5

2. C3H8 + O2 → CO2 + H2O

C3H8 + 5 O2 → 3 CO2 + 4 H2O

3. Ca2Si + Cl2 → CaCl2 + SiCl4Ca2Si + 4 Cl2 → 2 CaCl2 + SiCl4

4. Si + CO2 → SiC + SiO2

2 Si + CO2 → SiC + SiO2

Group Work: Balancing Equations

Instructions: › Work with the person next to you. › You have two worksheets to work on.

1. “Is it balanced?” Determine whether the chemical equation is balanced by counting atoms in the reactants and products.

2. “Balancing Act” Practice balancing equations.› What you do not finish is homework.› Ms. Boon will stamp your work when you are

done.› Once you have a stamp, you may check your

answers on the posted answer sheet.

Balancing Act Notes Atoms are not created or destroyed

during a chemical reaction. Scientists know that there must be the

same number of atoms on each side of the equation.

To balance the chemical equation, you must add coefficients to the different parts of the equation.

Chemical Reactions Reading You will work in groups of four or five at your table. Fold a sheet of paper into four squares. Label each square:

1. Synthesis reaction2. Decomposition reaction3. Single Replacement Reaction4. Double Replacement Reaction

You will be assigned one reaction. Read the section on that reaction, define it, give

an example, and draw a picture in your chart. (7 min)

Take turns sharing with your group. (8 min) Take notes on the other 3 reactions. If you finish early, read the entire article.

1. Synthesis Reactions Two substances combine to make one Synthesis means “to make”

+H2 H2OO2(g) (g) (l)

H H O O

H H H HO

H

H O

A + B AB

SYNTHESIS

Na + Cl2 NaCl

2. Decomposition Reactions One substance breaks down into 2 Decomposition means “to break down”

or “decay”

H HN

+NH3 H2(g)(l) N2 (g)

H

H HNH

AB A + B

Decomposition

NaCl Na + Cl2

one element replaces another in a compound

3. SINGLE REPLACEMENT

AB + C AC + B

Single Replacement Reaction

AB + C AC + B or CB + A

Single Replacement

NaBr + Cl2 NaCl + Br2

4. DOUBLE REPLACEMENT

Both elements in two compounds switch

places AB + CD AD +

CB

Double Replacement

NaBr + Pb2S3 Na2S + PbBr3

K2SO4 + Ba(OH)2

KOH + BaSO4

5. Combustion Reactions A hydrocarbon reacts with oxygen gas to

produce carbon dioxide and water vapor Combustion means to “burn in oxygen”

+CH4 H2OO2 CO2 +

+C2H4 H2OO2 CO2 +

+C6H12O6 H2OO2 CO2 +

Exit Slip! Balance and Identify the Type of Reaction.

1. Mg + O2 MgO

2. C3H8 + O2 CO2 + H2O

3. Na + Cl2 NaCl

4. C6H6 C + H2

5. FeO + CO2 FeCO3

Homework

Read pp. 271-274 Do problems pp. 271 #1-3, pp. 298 #1,

2, 3, 5, 6, 7