CHEMICAL REACTIONS AND EQUATIONS

Unit 5 Notes

Unit 5 Notes: Part 1 Types of Reactions

Chemical Reactions occur when bonds between atoms are formed or broken.

Indications that a chemical reaction has occurred: Color change Gas production (bubbles) Precipitate formed (solid formed from 2 liquids) Temperature change

Indications that a chemical reaction has occurred:

Gas production: http://www.youtube.com/watch?v=rjprBJAZECM&safe

=activePrecipitate: http://

www.youtube.com/watch?v=8RmVwz2fNGc&safe=active

Temperature change: http://www.youtube.com/watch?v=-RhQM4DHV4c&sa

fe=activeColor change (precipitate):

http://www.youtube.com/watch?v=pFovlKpPCbI&safe=active

What is a chemical equation?

Chemical Symbols: represent elements: Mg, S

Chemical Formulas: represent compounds: MgS

Chemical Equations: represent reactions: Mg + S MgS(reactants) (products)

Chemical reactions begin with reactants and end with products.

Symbols used in Equations:

Solid (s)Liquid (l)Gas (g)Aqueous solution (aq)Catalyst H2SO4

Escaping gas ( )Change of temperature ( )

5 types of Chemical Reactions:

1. Synthesis: substances combine to form one compound A + X AX

2H2 + O2 2H2O

 Practice predicting the products:

a. sodium metal reacts with chlorine gas

b. solid magnesium reacts with fluorine gas

5 types of Chemical Reactions:

2. Decomposition: compounds break down into smaller compounds and/or single elements AX A + X

2H2O 2H2 + O2

 Practice predicting the products:a. solid lead (IV) oxide decomposes:

b. aluminum nitride decomposes:

5 types of Chemical Reactions:

Decomposition exceptions:Carbonates and chlorates do not decompose into

single elements.

Carbonates decompose to carbon dioxide and a metal oxide.

CaCO3 CO2 + CaOChlorates decompose to oxygen gas and a

metal chloride2Al(ClO3)3 9O2 + 2AlCl3

5 types of Chemical Reactions:

3. Single Replacement Reactions: when one element replaces another in a compound; metal replaces metal; nonmetal replaces nonmetal A + BX AX + B (metal replaces metal) Y + BX BY + X (nonmetal replaces nonmetal) 2Al + 3Pb(NO3)2 3Pb + 2Al(NO3)3

Practice:  a. Zinc metal reacts with aqueous hydrochloric acid

 b. Sodium chloride solid reacts with fluorine gas

5 types of Chemical Reactions:

4. Double Replacement Reactions: two compounds either trade metals or trade nonmetals AX + BY AY + BX 2KI + Pb(NO3)2 PbI2 + 2KNO3

Practice:a. HCl(aq) + AgNO3(aq) b. CaCl2(aq) + Na3PO4(aq) c. Pb(NO3)2(aq) +  BaCl2(aq) d.  FeCl3(aq) +   NaOH(aq) e.  H2SO4(aq)   +  NaOH(aq) f. KOH(aq)  + CuSO4(aq)

5 types of Chemical Reactions:

5. Combustion Reactions: occurs when a hydrocarbon reacts with oxygen gas; products are always CO2 and H2O

Practice: a.   C5H12 + O2

 b. C10H22 + O2

Mixed Practice: ID the type of reaction, predict the products, balance

a.  BaCl2 + H2SO4

b.  C6H12 + O2 

c.  Zn + CuSO4

d.  Cs + Br2 

e.  FeCO3 

Part 2: Balancing Equations

Law of Conservation of Matter:matter cannot be created or destroyed

When a chemical reaction occurs, the amount of

Reactants must equal the amount of products. If an equation does not have equal numbers of atoms on each side, it is not balanced.

To balance an equation, use coefficients which are numbers in front of a symbol or formula. NEVER change the subscripts!!

Part 2: Balancing Equations

Al (s) + O2 (g) Al2O3 (s)What is wrong with this equation?

Fix it with coefficients!The final equation has 1 meanings:4 atoms of Al + 3 molecules of O2 yield 2

molecules of Al2O3

Practice Balancing Equations:

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

2. C3H8(g) + O2 CO2(g) + H2O

3. B4H10(g) + O2(g) B2O3(g) + H2O(l)

Practice Balancing Equations:

4. sodium phosphate + iron (III) oxide sodium oxide + iron (III) phosphate

5. sodium chloride + silver nitrate sodium nitrate + silver chloride

6. Iron (III) hydroxide iron (III) oxide + water

Practice Balancing Equations:

7. radium phosphide + sodium sodium phosphide + radium

8. cesium + sulfur cesium sulfide

9. potassium metal + chlorine gas potassium chloride

Practice Balancing Equations:

Diatomic molecules are atoms that always occur in pairs and should be written as pairs in equations:

Part 4: Energy Involved in Chemical Reactions:

Endothermic Reactions:

Exothermic Reactions:

Part 5: Activity Series:

In single replacement reactions you have to use an activity series to determine if an element can replace another:

 Li (More reactive)  Mg  Al  Zn  Cr  Fe  Pb  H  Cu  Hg (Less reactive)  Au

Part 5: Activity Series:

Elements can replace other elements that are more reactive (top can replace bottom)

Example: Pb2O3 + Cu à

These substance won’t react with each other. The copper is not strong enough or “active” enough to replace the lead.

Part 5: Activity Series:

In addition to more active metals replacing less active metals, nonmetals can also replace other nonmetals (Most reactive at top…fluorine)

Practice: a.  FeO2 + Cr à

b.  FeS + Hg à

c.  ZnCl2 + H2 à