Lesson 9Lesson 9

Chemical ReactionsChemical Reactions

Anything in black letters = write it in your notes (‘knowts’)

Quick Review…Quick Review…

2

Write the chemical formula for sodium carbonate

CO3-2Na+1

sodium ion carbonate ion

Na CO3

Section 1 – Counting AtomsSection 1 – Counting Atoms

Subscripts

2

Coefficient

Na2CO3

Subscripts represent the number of atoms in a compound.

Compound Number and type of atom in compound

Ca Cl Na C O

CaCl2

Na2CO3

NaCl

CaCO3

Coefficients represent the number of each element or compound

Compound Number and type of atom in compound

Ca Cl Na C O

3CaCl2

2Na2CO3

2NaCl

4CaCO3

Chemical equations represent chemical reactions

Reactants Products

Reactant mass = Product mass

# reactant atoms = # product atoms

Chemical equations must be balanced to obey the LAW!

Section 2 – Balancing Chemical EquationsSection 2 – Balancing Chemical Equations

Word Equations

“Sodium carbonate reacts with calcium chloride to produce sodium chloride and calcium carbonate”

Chemical Equations

Na2CO3 + CaCl2 NaCl + CaCO3

This is NOT balanced

Na2CO3 + CaCl2 NaCl + CaCO3

When balancing equations, never change subscripts.

Instead, add coefficients

2

subscripts coefficient

When balancing equations, never change subscripts. Instead, add coefficients

H2 + O2 → H2O22

Al + F2 → AlF32 23

NaClO3 → NaCl + O22 2 3

More on Chemical EquationsSymbols Used in Chemical Equations

Symbol Explanation

(s), (l), (g) Designates a reactant or product in the solid state, liquid state, or gaseous state; placed after the formula

(aq) Designates an aqueous solution; the substance is dissolved in water; placed after the formula

Indicates that heat is supplied to the reaction

A formula written above or below the yields sign indicates its use as a catalyst (in this example, platinum).

Δ

heat

Pt

or

Catalyst – substance that speeds up a chem. rxn but is not part of the chem. equation

Balancing Equations Help…

1. Balance 1 element at a time, from left to right.

2. Treat any polyatomic ions as single units if they are on both sides of the reaction.

Zn(OH) 2 + H3PO4 → Zn3(PO4)2 + H2O3 2 6

(OH) is NOT on both sides

There is a (PO4) on each side

Balancing Equations Hints…

3.Odd # atoms → even # atoms; multiply through by 2

4. Balance oxygen last, it just helps sometimes.

CH3OH + O2 → CO2 + H2O22 24

3

5. Remember, N2, O2, F2, Cl2, Br2, I2, H2

Quiz #1

1. FeCl3 + H2S → FeCl2 + HCl + S

2. MnO2 + HCl → MnCl2 + H2O + Cl2

3. Hydrochloric acid reacts with solid sodium hydrogen carbonate. The products formed are aqueous sodium

chloride, water, and carbon dioxide gas. Write a skeleton equation for this chemical reaction.

Balance the following chemical equations

Most chemical rxns will fit into 1 of 5 types.

1. Combination (Synthesis)

2. Decomposition

3. Single Replacement

4. Double Replacement

5. Combustion

Section 3 – Types of Chemical EquationsSection 3 – Types of Chemical Equations

1. Combination

A + B → AB

Magnesium metal and oxygen gas combine to form the compound magnesium oxide.

2Mg(s) + O2 (g) → 2 MgO(s)

2. Decomposition

AB → A + B

2HgO(s) 2Hg(l) + O2(g)heat

3. Single Replacement

A + BC → AB + C

2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)

4. Double Replacement

AB + CD → AC + BD

5. Combustion

A substance reacts with oxygen (O2) and releases energy

If the substance is a hydrocarbon, then CO2 and H2O are products,

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

Which type of reaction?

2K(s) + Cl2(g) → 2KCl(s)

S(s) + O2(g) → SO2(g)

2Fe(s) + 3S(g) → Fe2S3(s)

2NaN3(s) → 2Na(s) + 3N2(g)

H2O H2(g) + O2(g)electricity

K2CO3(aq) + BaCl2(aq) → 2KCl(aq) + BaCO3(s)

2KI(aq) + Pb(NO3)2(aq) → PbI2 + 2KNO3(aq)

Zn(s) + Cu(NO3)2(aq) → Cu(s) + Zn(NO3)2(aq)

Cl2(aq) + 2NaBr(aq) → 2NaCl(aq) + Br2(aq)

2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(g)

2Mg(s) + O2(g) → 2MgO(s)

Cu(s) + S(s) → CuS(s)

a) Al + F2 → AlF3

b) C3H8 + O2 → CO2 + H2O

c) FeSO4 + Ba(OH)2 → Fe(OH)2 + BaSO4

d) NaClO3 → NaCl + O2

Can you balance these?

Section 4 – Writing Chemical EquationsSection 4 – Writing Chemical Equations

Common acids:

H2SO4 – sulfuric acid

HCl – hydrochloric acid

HNO3 – nitric acid

Diatomic Molecules:

H2, N2, O2, F2, Cl2, Br2, I2

If the substance combusting is a hydrocarbon, then CO2 and H2O are products.

Write a balanced chemical equation for the combustion of propane (C3H8).

Write a balanced chemical equation for the combination of hydrogen gas and oxygen gas to form water. 

Write a balanced chemical reaction for the decomposition of copper(II) hydroxide into copper(II) oxide and water.  

Write a balanced chemical equation for the double replacement reaction of sodium nitrate with calcium chloride.  

Write a balanced chemical equation for the single replacement reaction of sodium metal with water to form sodium hydroxide and hydrogen gas.

4Ag + O2 → Ag2O2

What does a coefficient mean?

_____ atoms of Ag will react with _____ molecule(s) of O2 to form _____ formula units of Ag2O

A coefficient represents the combining ratio of reactants & products in a chemical rxn.

Exploratory info for next chapters…

4 Ag + O2 → Ag2O21. How many molecules of oxygen (O2) would be needed to react with 4 atoms of silver?

2. How many molecules of oxygen (O2) would be needed to react with 8 atoms of silver?

3. How many formula units of silver oxide would be formed in 1? In 2?

Exploratory info for next chapters…

4 Ag + O2 → Ag2O2

How many oxygen molecules would be needed to form 20 formula units of silver oxide?

How many atoms of silver would be required as well?

Exploratory info for next chapters…

4 Ag + O2 → Ag2O2

If 20 atoms of silver react with 20 molecules of oxygen, which reactant would be used up completely? Which reactant would be leftover?

How many formula units of silver oxide would be formed?

Exploratory info for next chapters…

Limiting Reactant -

Reactant that is completely used up; limits the amount of product that can be produced.

Excess Reactant -

Reactant that remains un-reacted; is not completely used up.

Exploratory info for next chapters…

1. How many molecules of CO are needed to produce 4 atoms of Fe?

6 CO molecules

Fe2O3 + CO → Fe + CO23 2 3

2. How much Fe2O3 is assumed to be present in the question above?

Assuming that there is at least 2 formula units of Fe2O3

Exploratory info for next chapters…